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1. a no a files lib a but do track lib a even though you re ignoring a files above TODO only ignore the root TODO file not subdir TODO build ignore all files in the build directory doc txt ignore doc notes txt but not doc server arch txt Viewing Your Staged and Unstaged Changes Ifthe git status command is too vague for you you want to know exactly what you changed not just which files were changed you can use the git diff command I ll cover git diff in more detail later but you ll probably use it most often to answer these two questions What have you changed but not yet staged And what have you staged that you are about to commit Although git status answers those questions very generally git diff shows you the exact lines added and removed the patch as it were CHAPTER 2 GIT BASICS 21 Let s say you edit and stage the README file again and then edit the benchmarks rb file without staging it If you run your status command you once again see something like this git status On branch master Changes to be committed use git reset HEAD lt file gt to unstage new file README i Changed but not updated use git add lt file gt to update what will be committed i modified benchmarks rb i To see what you ve changed but not yet staged type git diff with no other arguments git diff diff git a benchmarks rb b benchmarks rb index 3cb747f da
2. My Computer cfe teamone master Figure 3 38 Someone pushes rebased commits abandoning commits you ve based your work on At this point you have to merge this work in again even though you ve already done so Rebasing changes the SHA 1 hashes of these commits so to Git they look like new commits when in fact you already have the C4 work in your history see Figure 3 39 You have to merge that work in at some point so you can keep up with the other developer in the future After you do that your commit history will contain both the C4 and C4 commits which have different SHA 1 hashes but introduce the same work and have the same commit message If you run agit log when your history looks like this you ll see two commits that have the same author date and message which will be confusing Furthermore if you push this history back up to the server you ll reintroduce all those rebased commits to the central server which can further confuse people If you treat rebasing as a way to clean up and work with commits before you push them and if you only rebase commits that have never been available publicly then you ll be fine If you rebase commits that have already been pushed publicly and people may have based work on those commits then you may be in for some frustrating trouble CHAPTER 3 GIT BRANCHING 77 git team1 ourcompany com master My Computer master Figure 3 39 You merge in the sam
3. d6016bc require time for xmlschema 11d191e Merge branch defunkt into local Those are only some simple output formatting options to git log there are many more Table 2 2 lists the options I ve covered so far and some other common formatting options that may be useful along with how they change the output of the log command Table 2 2 Common git log Output Formatting Options Option Description p Show the patch introduced with each commit stat Show statistics for files modified in each commit shortstat Display only the changed insertions deletions line from the stat command name only Show the list of files modified after the commit information name status Show the list of files affected with added modified deleted information as well abbrev commit Show only the first few characters of the SHA 1 checksum instead of all 40 relative date Display the date in a relative format for example 2 weeks ago instead of using the full date format graph Display an ASCII graph of the branch and merge history beside the log output pretty Show commits in an alternate format Options include oneline short full fuller and format where you specify your own format Limiting Log Output In addition to output formatting options git log takes a number of useful limiting options that is options that let you show only a subset of commits You ve seen one such option already the 2 option which show only th
4. d Jett Bed xGhuGDjRsHj5Pik TI Tmp diff_G8ASUP Q index html KiDOCZYPE html PUBLIC W3C DTD XHTML 1 0 Strict EN lt IDOCTYPE html PUBLIC W3C DTD XHTML 1 0 Strict EN html xmins http www w3 org 1999 xhtml lt html xmlns http www w3 o0rg 1999 xhtml lt head gt lt head gt lt title gt Date Finder lt title gt lt title gt Date Finder lt title gt lt meta http equiv content type content text html cj lt meta http equiv content type content text html c lt link rel stylesheet href stylesheets application lt link rel stylesheet href stylesheets application lt javascript include tag prototype effects gt lt javascript include tag prototype effects gt lt head gt lt head gt lt body gt lt body gt Date Finder Date Finder Fform onsubmit return false lt form onsubmit return false lt text field tag date gt lt text field tag date K form gt lt form gt Kp id out gt lt p gt lt p id out gt lt p gt v_id footer gt please contact us at supportegithub cor lt div id footer gt please contact us at support github com Kscript type text javascript lt div gt few Form Element Observer lt script type text javascript date 0 5 new Form Element Observer function el value date new Ajax Request main chronic value 0 5 method get function el value onSuccess function
5. mark convert dir to mark dir You ll do this by creating an array of directories and using the index value as the mark because a mark must be an integer Your method looks like this marks def convert dir to mark dir if marks include dir marks dir end marks index dir 1 to s end Now that you have an integer representation of your commit you need a date for the commit metadata Because the date is expressed in the name of the directory you ll parse it out The next line in your print export file is date convert dir to date dir where convert dir to date is defined as def convert dir to date dir if dir current return Time now to i else dir dir gsub back year month day dir split return Time local year month day to i end end 217 218 CHAPTER 8 GIT AND OTHER SYSTEMS That returns an integer value for the date of each directory The last piece of meta information you need for each commit is the committer data which you hardcode in a global variable author Scott Chacon lt schacon example com gt Now you re ready to begin printing out the commit data for your importer The initial information states that you re defining a commit object and what branch it s on followed by the mark you ve generated the committer information and commit message and then the previous commit if any The code looks like this print the import information puts c
6. There are a lot of client side hooks This section splits them into committing workflow hooks e mail workflow scripts and the rest of the client side scripts Committing Workflow Hooks The first four hooks have to do with the committing process The pre commit hook is run first before you even type in a commit message It s used to inspect the snapshot that s about to be committed to see if you ve forgotten something to make sure tests run or to examine whatever you need to inspect in the code Exiting non zero from this hook aborts the commit although you can bypass it with git commit no verify You can do things like check for code style run lint or something equivalent check for trailing whitespace the default hook does exactly that or check for appropriate documentation on new methods The prepare commit msg hook is run before the commit message editor is fired up but after the default message is created It lets you edit the default message before the commit author sees it This hook takes a few options the path to the file that holds the commit mes sage so far the type of commit and the commit SHA 1 if this is an amended commit This hook generally isn t useful for normal commits rather it s good for commits where the default message is auto generated such as templated commit messages merge commits squashed commits and amended commits You may use it in conjunction with a commit template to programmatically in
7. git add benchmarks rb echo test line gt gt benchmarks rb git status it On branch master Changes to be committed modified benchmarks rb Changed but not updated modified benchmarks rb TE HH HH HHH H Now you can use git diff to see what is still unstaged git diff diff git a benchmarks rb b benchmarks rb index e445e28 86b2f7c 100644 a benchmarks rb b benchmarks rb 127 3 127 4 end main pp Grit GitRuby cache client stats test line You can use git diff cached to see what you ve staged so far git diff cached diff git a benchmarks rb b benchmarks rb index 3cb747f e445e28 100644 a benchmarks rb b benchmarks rb 36 6 36 10 def main commit parents 0 parents 0 parents 0 end run_code x commits 1 do git commits size CHAPTER 2 GIT BASICS 23 end run code x commits 2 do log git commits master 15 log size Committing Your Changes Now that your staging area is set up the way you want it you can commit your changes Remember that anything that is still unstaged any files you have created or modified that you haven t run git add on since you edited them won t go into this commit They will stay as modified files on your disk In this case the last time you ran git status you saw that everything was staged so you re ready to commit your changes The simplest way to commit is to type git commit git commit
8. 195 197 access path 197 active contributor size 110 add command 18 19 150 153 230 add option 226 aliases 44 45 am command 131 133 191 amend option 32 33 ancestry references 147 annotated tags 39 141 234 a option 24 apply command 130 archive command 141 asterisk 20 61 attributes 184 190 binary files 184 186 exporting repository 189 190 keyword expansion 186 189 merge strategies 190 authentication generating SSH public key 85 86 author 29 author option 30 authorization 86 87 authorized keys method 86 87 auto completion 43 44 auto gc command 244 B backslash V 25 bare option 83 bare repository 79 84 base path option 95 benevolent dictator 109 binary files 184 186 diffing 184 186 identifying 184 binary search 163 164 bisect command 163 164 bisect start command 164 BitKeeper 5 blame command 162 blobs 226 branch command 48 60 233 branches branching basic 53 56 checking out remote 133 creating 48 creating from stash 156 deleting 61 hotfix 55 issues 208 209 long running 63 management of 60 61 merge conflicts 58 60 merging 57 70 overview 47 52 proposed 63 rebasing 70 76 remote 64 65 68 69 sharing 68 69 specifying multiple points 149 Subversion 209 210 switching 50 52 topic 63 64 130 137 139 140 tracking 69 workflows 61 64 branches directory 224 branch references 145 b switch git checkout command 53 build nu
9. He oH HE HE You can see that Git re modifies the files you uncommitted when you saved the stash In this case you had a clean working directory when you tried to apply the stash and you tried to apply it on the same branch you saved it from but having a clean working directory and apply ing it on the same branch aren t necessary to successfully apply a stash You can save a stash on one branch switch to another branch later and try to reapply the changes You can also have modified and uncommitted files in your working directory when you apply a stash Git gives you merge conflicts if anything no longer applies cleanly The changes to your files were reapplied but the file you staged before wasn t restaged To do that you must run the git stash apply command with a index option to tell the com mand to try to reapply the staged changes If you had run that instead you d have gotten back to your original position git stash apply index On branch master Changes to be committed use git reset HEAD lt file gt to unstage modified index html Changed but not updated use git add file to update what will be committed modified lib simplegit rb He ct oit it HE HE HEHE The apply option only tries to apply the stashed work you continue to have it on your stack To remove it you can run git stash drop with the name of the stash to remove git stash list stash8 0 WIP on master 049d0
10. Now that you can specify individual commits let s see how to specify ranges of commits This is particularly useful for managing your branches if you have a lot of branches you can use range specifications to answer questions such as What work is on this branch that I haven t yet merged into my main branch 148 CHAPTER 6 GIT TOOLS Double Dot The most common range specification is the double dot syntax This basically asks Git to resolve a range of commits that are reachable from one commit but aren t reachable from another For example say you have a commit history that looks like Figure 6 1 O O 0 O koros Figure 6 1 Example history for range selection You want to see what is in your experiment branch that hasn t yet been merged into your master branch You can ask Git to show you a log of just those commits with master experiment that means all commits reachable by experiment that aren t reachable by master For the sake of brevity and clarity in these examples I ll use the letters of the com mit objects from the diagram in place of the actual log output in the order that they would display git log master experiemnt D C If on the other hand you want to see the opposite all commits in master that aren t in experiment you can reverse the branch names experiment master shows you everything in master not reachable from experiment git log experiment master F E This is useful i
11. YOUF DIM TOO jie rod mca e dti nas 12 Checking Your SettingS 00 0 ccc cece eee 12 Getting Help iscsi dco cseeed cease eae IRR RD ad leteamaneens 13 SUMMA stre eR ee ee RE de 13 vii viii CONTENTS CHAPTER 2 Git BASIGS ooo e EGER aa e sa R 15 Getting a Git Repository 0 ccc cece eens 15 Initializing a Repository in an Existing Directory 15 Cloning an Existing Repository 0c c cece eee 16 Recording Changes to the Repository cece eee eee 16 Checking the Status of Your Files 0 0005 17 Tracking New Files 0 0 0 ccc cece cece eee eee ees 18 Staging Modified Files 0 0 0 ccc cece eee eee ees 18 Ignoring Files 0 ccc ccc ccc cece eee eee eens 20 Viewing Your Staged and Unstaged Changes 20 Committing Your Changes 0 0 c cece eee ences 23 Skipping the Staging Area 20 cece cece eee ees 24 Removing Files 24 Moving Files 2 0 ccc ccc ccc cece cence ence eens 25 Viewing the Commit History 26 Limiting Log Output 0 00 cece eee eee 30 Using a GUI to Visualize History 0 cece eee 31 Undoing Things 0 ccc ccc cece a tee e ei 32 Changing Your Last Commit 0 0 cece eee eee 32 Unstaging a Staged File 0 0 cece eee cece eee ee 33 Unmodifying a Modified File 0
12. after Limit the commits to those made after the specified date until before Limit the commits to those made before the specified date author Only show commits in which the author entry matches the specified string committer Only show commits in which the committer entry matches the specified string For example if you want to see which commits in the Git source code history were com mitted by Junio Hamano and were not merges in the month of October 2008 you can run something like this git log pretty h s author gitster since 2008 10 01 before 2008 11 01 no merges t 5610e3b Fix testcase failure when extended attribute acd3b9e Enhance hold lock file for _ update append 563754 demonstrate breakage of detached checkout wi d1a43f2 reset hard read tree reset u remove un 51a94af Fix checkout track b newbranch on detac boadiie pull allow git pull origin something cur Of the nearly 20 000 commits in the Git source code history this command shows the 6 that match those criteria Using a GUI to Visualize History If you like to use a more graphical tool to visualize your commit history you may want to take a look at a Tcl Tk program called gitk that is distributed with Git gitk is basically a visual git log tool and it accepts nearly all the filtering options that git log does If you type gitk on the command line in your project you should see something like Figure 2 2
13. git objects fa 49b077972391ad58037050f2a75f74e3671e92 new txt git objects fd f4fc3344e67a3b0681836878b6c4951e3bi5f3d commit 1 If you follow all the internal pointers you get an object graph something like Figure 9 3 bak 1a410e 3c4e9c third commit tree new txt test txt 1f7a7a cac ca 155eb test txt new txt T new file fdf4fc d8329f 83baae first commit tree test txt version 1 Figure 9 3 All the objects in your Git directory CHAPTER 9 GIT INTERNALS 231 Object Storage I mentioned earlier that a header is stored with the content Let s take a minute to look at how Git stores its objects You ll see how to store a blob object in this case the string what is up doc interactively in the Ruby scripting language You can start up interactive Ruby mode with the irb command irb content what is up doc what is up doc Git constructs a header that starts with the type of the object in this case a blob Then it adds a space followed by the size of the content and finally a null byte gt gt header blob content length o gt blob 16 000 Git concatenates the header and the original content and then calculates the SHA 1 checksum of that new content You can calculate the SHA 1 value of a string in Ruby by including the SHA1 digest library with the require command and then calling Digest SHA1 hexdigest with the string gt gt store
14. header content gt blob 16 000what is up doc gt gt require digest sha1 gt true gt gt shal Digest SHA1 hexdigest store gt bd9dbf5aae1a3862dd1526723246b20206e5fc37 Git compresses the new content with zlib which you can do in Ruby with the zlib library First you need to require the library and then run Zlib Deflate deflate on the content require zlib true zlib content Zlib Deflate deflate store gt x 234K 312 3110RO4c 3317H 0310 V 3200H 3110 266 a 000_ 034 a 235 Finally you ll write your zlib deflated content to an object on disk You ll determine the path of the object you want to write out the first two characters of the SHA 1 value being the subdirectory name and the last 38 characters being the filename within that directory In Ruby you can use the FileUtils mkdir p function to create the subdirectory if it doesn t exist Then open the file with File open and write out the previously zlib compressed con tent to the file with a write call on the resulting file handle gt gt path git objects sha1 0 2 sha1 2 38 gt git objects bd 9dbf5aae1a3862dd1526723246b20206e5fc37 gt gt require fileutils true FileUtils mkdir p File dirname path git objects bd gt gt File open path w f f write zlib content gt 32 232 CHAPTER 9 GIT INTERNALS That s it you ve created a valid Git blob object Al
15. name only pretty format ref you have to use files modified git diff index cached name only HEAD CHAPTER 7 CUSTOMIZING GIT 201 But those are the only two differences otherwise the script works the same way One caveat is that it expects you to be running locally as the same user you push as to the remote machine If that is different you must set the user variable manually The last thing you have to do is check that you re not trying to push non fast forwarded references but that is a bit less common To get a reference that isn t a fast forward you either have to rebase past a commit you ve already pushed up or try pushing a different local branch up to the same remote branch Because the server will tell you that you can t push a non fast forward anyway and the hook prevents forced pushes the only accidental thing you can try to catch is rebasing com mits that have already been pushed Here is an example pre rebase script that checks for that It gets a list of all the commits you re about to rewrite and checks whether they exist in any of your remote references If it sees one that is reachable from one of your remote references it aborts the rebase usr bin env ruby base branch ARGV O if ARGV 1 topic branch ARGV 1 else topic branch HEAD end target shas git rev list base branchj f topic branch split Mn remote refs git branch r split n map r r strip t
16. oldrev ARGV 1 newrev ARGV 2 user ENV USER puts Enforcing Policies n refname oldrev 0 6 newrev 0 6 Yes I m using global variables Don t judge me it s easier to demonstrate in this manner 194 CHAPTER 7 CUSTOMIZING GIT Enforcing a Specific Commit Message Format Your first challenge is to enforce that each commit message must adhere to a particular for mat Just to have a target assume that each message has to include a string that looks like ref 1234 because you want each commit to link to a work item in your ticketing system You must look at each commit being pushed up see if that string is in the commit message and if the string is absent from any of the commits exit non zero so the push is rejected You can get a list of the SHA 1 values of all the commits that are being pushed by taking the newrev and oldrev values and passing them to a Git plumbing command that is called git rev list This is basically the git log command but by default it prints out only the SHA 1 values and no other information So to get a list of all the commit SHAs introduced between one commit SHA and another you can run something like this git rev list 538c33 d14fc7 d14fc7c847ab946ec395904087783c69b031bdfb7 9f585da4401b0a3999e84113824d15245c13fO0be 234071a1be950e238d078e6141f5cd20c1e61ad3 dfa04c9ef3d5197182f13fb5b9b1fb7717d2222a 17716ecof1ff5c77eff40b7fe912f9f6cfd0e475 You can take tha
17. should probably begin tracking those files and do an initial commit You can accomplish that with a fewgit add commands that specify the files you want to track followed by a commit git add c git add README git commit m initial project version I ll go over what these commands do in just a minute At this point you have a Git reposi tory with tracked files and an initial commit 15 16 CHAPTER 2 GIT BASICS Cloning an Existing Repository If you want to get a copy of an existing Git repository for example a project you d like to contribute to the command you need is git clone If you re familiar with other VCS sys tems such as Subversion you ll notice that the command is clone and not checkout This is an important distinction Git receives a copy of nearly all data that the server has Every ver sion of every file for the history of the project is pulled down when you run git clone In fact if your server disk gets corrupted you can use any of the clones on any client to set the server back to the state it was in when it was cloned you may lose some server side hooks and such but all the versioned data would be there see Chapter 4 for more details You clone a repository with git clone url For example if you want to clone the Ruby Git library called Grit you can do so like this git clone git github com schacon grit git That creates a directory named grit initializes a git directory inside it
18. stat option prints below each commit entry a list of modified files how many files were changed and how many lines in those files were added and removed It also puts a summary of the information at the end Another really useful option is pretty This option changes the log output to formats other than the default A few prebuilt options are available for you to use The oneline option prints each commit on a single line which is useful if you re looking at a lot of commits In addition the short full and fuller options show the output in roughly the same format but with less or more information respectively CHAPTER 2 GIT BASICS 29 git log pretty oneline ca82a6dff817ec66f44342007202690393763949 changed the version number 085bb3bcb608e1e8451d4b2432f8ecbe6306e7e7 removed unnecessary test code 311bef06a3f659402fe7563abf99ad00de2209e6 first commit The most interesting option is format which allows you to specify your own log output format This is especially useful when you re generating output for machine parsing because you specify the format explicitly you know it won t change with updates to Git git log pretty format h Zan ar Xs ca82a6d Scott Chacon 11 months ago changed the version number 085bb3b Scott Chacon 11 months ago removed unnecessary test code allbefo Scott Chacon 11 months ago first commit Table 2 1 lists some of the more useful options that format takes Table 2 1 Formatting O
19. vim TODO git commit am add reset task master fbff5bc add reset task 1 files changed 1 insertions 0 deletions Now Jessica pushes her work up to the server Jessica s Machine git push origin master To jessica githost simplegit git 1edee6b fbff5bc master gt master John tries to push his change up too John s Machine git push origin master To john githost simplegit git rejected master gt master non fast forward error failed to push some refs to john githost simplegit git John isn t allowed to push because Jessica has pushed in the meantime This is especially important to understand if you re used to Subversion because you ll notice that the two devel opers didn t edit the same file Although Subversion automatically does such a merge on the server if different files are edited in Git you must merge the commits locally John has to fetch Jessica s changes and merge them in before he will be allowed to push git fetch origin From john githost simplegit 049d078 fbff5bc master gt origin master 114 CHAPTER 5 DISTRIBUTED GIT At this point John s local repository looks something like Figure 5 4 master nae origin master Figure 5 4 John s initial repository John has a reference to the changes Jessica pushed up but he has to merge them into his own work before he is allowed to push git merge origin master Merge made by recursive TODO
20. 0 1 TODO 2 unchanged 1 1 index html 3 unchanged 5 1 lib simplegit rb Update CHAPTER 6 GIT TOOLS 151 The next to each file means the file is selected to be staged If you press Enter after typing nothing at the Update gt gt prompt Git takes anything selected and stages it for you Update gt gt updated 2 paths Commands 1 status 2 update 3 revert 4 add untracked 5 patch 6 diff 7 quit 8 help What now 1 staged unstaged path 1 0 1 nothing TODO 2 1 1 nothing index html 3 unchanged 5 1 lib simplegit rb Now you can see that the TODO and index html files are staged and the simplegit rb file is still unstaged If you want to unstage the TODO file at this point you use the 3 or r for revert option Commands 1 status 2 update 3 revert 4 add untracked 5 patch 6 diff 7 quit 8 help What now 3 staged unstaged path 1 0 1 nothing TODO 2 1 1 nothing index html 3 unchanged 5 1 lib simplegit rb Revert 1 staged unstaged path 21 0 1 nothing TODO 2 1 1 nothing index html 3 unchanged 5 1 lib simplegit rb Revert gt gt enter reverted one path Looking at your Git status again you can see that you ve unstaged the TODO file Commands 1 status 2 update 3 revert 4 add untracked 5 patch 6 diff 7 quit 8 help What now 1 staged unstaged path 1 unchanged 0 1 TODO 1 1 nothing index html 3 unchanged 5 1 lib simplegit rb
21. 152 CHAPTER 6 GIT TOOLS To see the diff of what you ve staged you can use the 6 or d for diff command It shows you a list of your staged files and you can select the ones for which you would like to see the staged diff This is much like specifying git diff cached on the command line Commands 1 status 2 update 3 revert 4 add untracked 5 patch 6 diff 7 quit 8 help What now 6 staged unstaged path 1 1 1 nothing index html Review diff gt gt 1 diff git a index html b index html index 4d07108 4335f49 100644 a index html b index html 16 7 416 7 Date Finder p id out gt lt p gt div id footer gt contact support github com lt div gt lt div id footer contact email support github com lt div gt script type text javascript With these basic commands you can use the interactive add mode to deal with your stag ing area a little more easily Staging Patches It s also possible for Git to stage certain parts of files and not the rest For example if you make two changes to your simplegit rb file and want to stage one of them and not the other doing so is very easy in Git From the interactive prompt type 5 or p for patch Git will ask you which files you would like to partially stage then for each section of the selected files it will display hunks of the file diff and ask if you would like to stage them one by one diff git a lib simplegit rb
22. 172 no merged option 61 not option 134 149 0 objects 225 232 blobs 226 commit 228 230 packing 235 238 removing 247 250 storage 231 232 tag 234 235 tree 226 228 objects directory 224 232 objects info packs file 241 octopus strategy 171 origin remote 35 P packed refs file 245 packfiles 235 238 patches accepting and applying 130 applying from e mail 130 133 in large projects 127 129 staging 152 153 patch sets 2 pbxproj files 184 Perforce migrating to Git from 214 216 Perforce Visual Merge Tool P4Merge 179 pipe character 195 plumbing commands 223 224 policy enforcing server example 193 201 p option 134 porcelain commands 223 post checkout hook 192 post commit hook 191 post merge hook 192 post receive hook 192 pre commit hook 191 200 prefix option 228 prepare commit msg hook 191 pre rebase hook 192 201 pre receive script 193 print_export method 217 private projects managed teams 118 123 small team 112 118 project root making subdirectory to 161 projects applying patches from e mail 130 133 checking out remote branches 133 cloning with submodules 167 169 commit guidelines for 111 112 contributing to 110 129 determining what is introduced in 134 135 generating build numbers 141 integrating contributed work into 135 140 maintaining 130 142 preparing releases 141 private managed team 118 123 private small team 112 118 public large 127 129
23. 5 days ago initial commit schacon iGitViemController xib 5 days ago initial commit schacon iGit Prefix pch 5 days ago initial commit schacon main m 5 days ago initial commit schacon Figure 4 13 A GitHub main project page 103 104 CHAPTER 4 GIT ON THE SERVER When people visit your project they see this page It contains tabs to different aspects of your projects The Commits tab shows a list of commits in reverse chronological order similar to the output of the git log command The Network tab shows all the people who have forked your project and contributed back The Downloads tab allows you to upload project binaries and link to tarballs and zipped versions of any tagged points in your project The Wiki tab pro vides a wiki where you can write documentation or other information about your project The Graphs tab has some contribution visualizations and statistics about your project The main Source tab that you land on shows your project s main directory listing and automatically ren ders the README file below it if you have one This tab also shows a box with the latest commit information Forking Projects If you want to contribute to an existing project to which you don t have push access GitHub encourages forking the project When you land on a project page that looks interesting and you want to hack on it a bit you can click the fork button in the project header to have GitHub copy that project to your u
24. CHAPTER 2 GIT BASICS 33 This command takes your staging area and uses it for the commit If you have made no changes since your last commit for instance you run this command it immediately after your previous commit then your snapshot will look exactly the same and all you ll change is your commit message The same commit message editor fires up but it already contains the message of your previous commit You can edit the message the same as always but it overwrites your previous commit As an example if you commit and then realize you forgot to stage the changes in a file you wanted to add to this commit you can do something like this git commit m initial commit git add forgotten file git commit amend All three of these commands end up with a single commit the second command replaces the results of the first Unstaging a Staged File The next two sections demonstrate how to wrangle your staging area and working directory changes The nice part is that the command you use to determine the state of those two areas also reminds you how to undo changes to them For example let s say you ve changed two files and want to commit them as two separate changes but you accidentally type git add and stage them both How can you unstage one of the two The git status command reminds you git add git status On branch master Changes to be committed use git reset HEAD lt file gt to unstage modifi
25. Changes to be committed use git reset HEAD lt file gt to unstage renamed README txt gt README He HEHE However this is equivalent to running something like this mv README txt README git rm README txt git add README Git figures out that it s a rename implicitly so it doesn t matter if you rename a file that way or with the mv command The only real difference is that mv is one command instead of three it s a convenience function More important you can use any tool you like to rename a file and address the add rm later before you commit Viewing the Commit History After you have created several commits or if you have cloned a repository with an existing commit history you ll probably want to look back to see what has happened The most basic and powerful tool to do this is the git log command These examples use a very simple project called simplegit that I often use for demonstra tions To get the project run git clone git github com schacon simplegit progit git When you run git log in this project you should get output that looks something like this git log commit ca82a6dff817ec66f44342007202690a93763949 Author Scott Chacon lt schacon gee mail com gt Date Mon Mar 17 21 52 11 2008 0700 changed the version number commit 085bb3bcb608e1e8451d4b2432f8ecbe6306e7e7 Author Scott Chacon schaconggee mail com Date Sat Mar 15 16 40 33 2008 0700 removed unnecessary test code
26. Counting objects 19 done Delta compression using 2 threads Compressing objects 100 14 14 done Writing objects 100 19 19 done Total 19 delta 3 reused 16 delta 1 Let s see how much space you saved git count objects v count 8 size 2040 in pack 19 packs 1 250 CHAPTER 9 GIT INTERNALS size pack 7 prune packable 0 garbage O The packed repository size is down to 7K which is much better than 2MB You can see from the size value that the big object is still in your loose objects so it s not gone but it won t be transferred on a push or subsequent clone which is what s important If you really wanted to you could remove the object completely by running git prune expire Summary You should have a pretty good understanding of what Git does in the background and to some degree how it s implemented This chapter has covered a number of plumbing commands commands that are lower level and simpler than the porcelain commands you ve learned about in the rest of the book Understanding how Git works at a lower level should make it easier to understand why it s doing what it s doing and also to write your own tools and help ing scripts to make your specific workflow work for you Git as a content addressable filesystem is a very powerful tool that you can easily use as more than just a VCS I hope you can use your newfound knowledge of Git internals to imple ment your own cool application of
27. Importing from Subversion 00 cece eee ee eee 101 Adding Collaborators 0 0 0 c ccc ete eee ees 102 pod ue 103 Forking ProjectS 0 ccc ccc cece cee eee eens 104 GitHub Summary erse ia a a e a a E 105 SUMMAN 4 cun nese i a E E EE E 105 Distributed Git oou 107 Distributed WorkfloWS 000 0 cece ccc cence eee ees 107 Centralized Workflow 00 00 cece eee eee eens 107 Integration Manager Workflow 00 c cece eens 108 Dictator and Lieutenants Workflow 0 0005 109 Contributing to a Project 110 Commit Guidelines 111 Private Small Team 112 Private Managed Team 00 0 cece cece eee eens 118 Public Small Project 124 Public Large Project 00 00 c cece eee eee neces 127 SUMMAlY ennan ccc erranera 129 Maintaining a Project 0 0 ccc ccc cece RR 130 Working in Topic Branches 20 c eee eee ee eee 130 Applying Patches from E mail cece eae 130 Checking Out Remote Branches 0 00 eeu ees 133 Determining What Is Introduced sussusssssssss 134 Integrating Contributed Work 00 c cece eee eee 135 Tagging Your Releases 0 0 c cece cence eens 140 Generating a Build Number 000 0 cee eee ees 141 Preparing a Release 0 ccc cece cece teen eens 141 The Shortlog 0 c
28. Many times when working with Git you may want to revise your commit history for some reason One of the great things about Git is that it allows you to make decisions at the last pos sible moment You can decide what files go into which commits right before you commit with the staging area you can decide that you didn t mean to be working on something yet with the stash command and you can rewrite commits that already happened so they look like they happened in a different way This can involve changing the order of the commits changing messages or modifying files in a commit squashing together or splitting apart commits or removing commits entirely all before you share your work with others In this section you ll cover how to accomplish these very useful tasks so that you can make your commit history look the way you want before you share it with others Changing the Last Commit Changing your last commit is probably the most common rewriting of history that you ll do You ll often want to do two basic things to your last commit change the commit message or change the snapshot you just recorded by adding changing and removing files If you only want to modify your last commit message it s very simple git commit amend CHAPTER 6 GIT TOOLS 157 That drops you into your text editor which has your last commit message in it ready for you to modify the message When you save and close the editor the editor writes a new com
29. No changes between current HEAD and refs remotes trunk Resetting to the latest refs remotes trunk 208 CHAPTER 8 GIT AND OTHER SYSTEMS It s important to remember that unlike Git which requires you to merge upstream work you don t yet have locally before you can push git svn makes you do that only if the changes conflict If someone else pushes a change to one file and then you push a change to another file your dcommit will work fine git svn dcommit Committing to file tmp test svn trunk M configure ac Committed r84 M autogen sh r83 8aa54a74d452f82eee10076ab2584c1fc424853b trunk M configure ac 184 cdbac939211ccb18aa744e581e46563af5d962d0 trunk W d2f23b80f67aaaa1f6f5aaef48fce3263ac71a92 and refs remotes trunk differ using rebase 1100755 100755 efa5a59965fbbb5b2b0a12890f1b351bb5493c18 015e4c98c482f0fa71e4d5434338014530b37fa6 M autogen sh First rewinding head to replay your work on top of it Nothing to do This is important to remember because the outcome is a project state that didn t exist on either of your computers when you pushed If the changes are incompatible but don t conflict you may get issues that are difficult to diagnose This is different than using a Git server in Git you can fully test the state on your client system before publishing it whereas in SVN you can t ever be certain that the states immediately before commit and after commit are identical You should also run th
30. area and lightweight topic branching and merging Now you ll explore a number of very powerful things that Git can do that you may not necessarily use on a day to day basis but that you may need at some point Revision Selection Git allows you to specify specific commits or a range of commits in several ways They aren t necessarily obvious but are helpful to know Single Revisions You can obviously refer to a commit by the SHA 1 hash that it s given but there are more human friendly ways to refer to commits as well This section outlines the various ways you can refer to a single commit Short SHA Git is smart enough to figure out what commit you meant to type if you provide the first few characters as long as your partial SHA 1 is at least four characters long and unambiguous that is only one object in the current repository begins with that partial SHA 1 For example to see a specific commit suppose you run agit log command and identify the commit where you added certain functionality git log commit 734713bc047487bf7eac9674765ae793478c50d3 Author Scott Chacon lt schacon gmail com gt Date Fri Jan 2 18 32 33 2009 0800 fixed refs handling added gc auto updated tests commit d921970aadf03b3cf0e71becdaab3147ba71cdef Merge 1cOO2dd 35cfb2b Author Scott Chacon lt schacon gmail com gt Date Thu Dec 11 15 08 43 2008 0800 143 144 CHAPTER 6 GIT TOOLS Merge commit phedders rdocs commit 1c002d
31. command just shows the commit git show v1 4 1w commit 15027957951b64cf874c3557a0f3547bd83b3ff6 Merge 4a447f7 a6b4c97 Author Scott Chacon lt schacon gee mail com gt Date Sun Feb 8 19 02 46 2009 0800 Merge branch experiment Verifying Tags To verify a signed tag you usegit tag v tag name This command uses GPG to verify the signature You need the signer s public key in your keyring for this to work properly git tag v v1 4 2 1 object 883653babd8ee7ea23e6a5c392bb739348b1eb61 type commit tag v1 4 2 1 tagger Junio C Hamano junkioGcox net 1158138501 0700 GIT 1 4 2 1 Minor fixes since 1 4 2 including git mv and git http with alternates gpg Signature made Wed Sep 13 02 08 25 2006 PDT using DSA key ID F3119B9A gpg Good signature from Junio C Hamano lt junkio cox net gt gpg aka jpeg image of size 1513 Primary key fingerprint 3565 2A26 2040 E066 C9A7 4A7D COC6 D9A4 F311 9B9A If you don t have the signer s public key you get something like this instead gpg Signature made Wed Sep 13 02 08 25 2006 PDT using DSA key ID F3119B9A gpg Can t check signature public key not found error could not verify the tag v1 4 2 1 42 CHAPTER 2 GIT BASICS Tagging Later You can also tag commits after you ve moved past them Suppose your commit history looks like this git log pretty oneline 15027957951b64cf874c3557a0f3547bd83b3ff6 Merge branch experiment a6b4c97498bd301d84096da251c
32. database xml stays at whatever version you originally had Git Hooks Like many other Version Control Systems Git has a way to fire off custom scripts when certain important actions occur There are two groups of these hooks client side and server side The client side hooks are for client operations such as committing and merging The server side hooks are for Git server operations such as receiving pushed commits You can use these hooks for all sorts of reasons and you ll learn about a few of them here Installing a Hook The hooks are all stored in the hooks subdirectory of the Git directory In most projects that s git hooks By default Git populates this directory with a bunch of example scripts many of which are useful by themselves but they also document the input values of each script All the examples are written as shell scripts with some Perl thrown in but any properly named executable scripts will work fine you can write them in Ruby or Python or what have you For post 1 6 versions of Git these example hook files end with sample you ll need to rename them For pre 1 6 versions of Git the example files are named properly but are not executable To enable a hook script put a file in the hooks subdirectory of your Git directory that is named appropriately and is executable From that point forward it should be called I ll cover most of the major hook filenames here CHAPTER 7 CUSTOMIZING GIT 191 Client Side Hooks
33. first commit with submodule rack cd rack git log 1 commit 08d709f78b8c5b0fbeb7821e37fa53e69afcf433 Author Christian Neukirchen lt chneukirchen gmail com gt Date Wed Mar 25 14 49 04 2009 0100 Document version change Cloning a Project with Submodules Here you ll clone a project with a submodule in it When you receive such a project you get the directories that contain submodules but none of the files yet git clone git github com schacon myproject git Initialized empty Git repository in opt myproject git remote Counting objects 6 done remote Compressing objects 100 4 4 done remote Total 6 delta 0 reused O delta 0 Receiving objects 100 6 6 done cd myproject 1s 1 total 8 Yw r r 1 schacon admin 3 Apr 9 09 11 README drwxr xr x 2 schacon admin 68 Apr 9 09 11 rack 1s rack The rack directory is there but empty You must run two commands git submodule init to initialize your local configuration file and git submodule update to fetch all the data from that project and check out the appropriate commit listed in your superproject git submodule init Submodule rack git github com chneukirchen rack git registered for path rack git submodule update Initialized empty Git repository in opt myproject rack git remote Counting objects 3181 done remote Compressing objects 100 1534 1534 done remote Total 3181 delta 1951 reused 2623 delta 1603 Rece
34. flow One central hub or repository can accept code and everyone synchronizes their work to it A number of developers are nodes consumers of that hub and synchronize to that one place see Figure 5 1 This means that if two developers clone from the hub and both make changes the first developer to push their changes back up can do so with no problems The second developer must merge in the first one s work before pushing changes up so as not to overwrite the first developer s changes This concept is true in Git as it is in Subversion or any CVCS and this model works perfectly in Git If you have a small team or are already comfortable with a centralized workflow in your company or team you can easily continue using that workflow with Git Simply set up a single repository and give everyone on your team push access Git won t let users overwrite each other If one developer clones makes changes and then tries to push their changes while 107 108 CHAPTER 5 DISTRIBUTED GIT another developer has pushed in the meantime the server will reject that developer s changes They will be told that they re trying to push non fast forward changes and that they won t be able to do so until they fetch and merge This workflow is attractive to a lot of people because it s a paradigm that many are familiar and comfortable with shared repository developer developer developer Figure 5 1 Centraliz
35. 0 c ccc ccc a EREE 63 Remote Branches 00 0 cece cece cece eee e ene en tenes 64 PUSHING 3 2 csse PE oct ct ated adr oce oe tech ad 68 Tracking Branches 69 Deleting Remote Branches 00 0cc ee anera 69 Hebasintgji sene Eae Re eee Rr PeNbK Rae e ew ade leads 70 The Basic Rebase 6 2245 44e0eseeee eid ees ES 70 More Interesting RebaseS 0 00 cece eee ee eee 72 The Perils of Rebasing 00 0000 cece cece eens 74 SUMMARY STRE ER ECCO EROR TEE TROIS 77 Git on the Server 00 000000000 cece cece 79 The Protocols 2 0 ccc cece nee eee I 79 Local Protocol ter erre rte ohh ed 80 The SSH Protocol IRI 81 The Git Protocol 2 0 ees 81 The HTTP S Protocol 0 ccc cece eee eee es 82 Getting Git on a Server 83 Putting the Bare Repository on a Server 0 05 84 SIUE cannons Mote pedaewsetdaw Erani dace 85 Suis ls 85 Generating Your SSH Public Key 00 e cece eee 85 Setting Up the Server 0 0 0 ccc ccc ccc eee nen eens 86 PUDIG ACCOSS oobis Re Reina Rei te 88 Hn TMMMTMT 90 GEI 91 Gib DB Ouch omen tee esate mane atte ueterum et 95 CONTENTS CHAPTER 5 CHAPTER 6 Hosted Gib ie dete ned net eds eost nee n anda nes 96 C7 7 0 ReneS eae iran ne ea REEE HE Se 97 Setting Up a User Account 00 c cece eee eee ee 97 Creating a New Repository 0 cece eee eee eee 99
36. CHAPTER 2 GIT BASICS commit a11bef06a3f659402fe7563abf99ad00de2209e6 Author Scott Chacon lt schacon gee mail com gt Date Sat Mar 15 10 31 28 2008 0700 first commit By default with no arguments git log lists the commits made in that repository in reverse chronological order That is the most recent commits show up first As you can see this command lists each commit with its SHA 1 checksum the author s name and e mail the date written and the commit message A huge number and variety of options to the git log command are available to show you exactly what you re looking for Here I ll show you some of the most used options One of the more helpful options is p which shows the diff introduced in each commit You can also use 2 which limits the output to only the last two entries git log p 2 commit ca82a6dff817ec66f44342007202690a93763949 Author Scott Chacon lt schacon gee mail com gt Date Mon Mar 17 21 52 11 2008 0700 changed the version number diff git a Rakefile b Rakefile index a874b73 8f94139 100644 a Rakefile b Rakefile 5 7 45 7 require rake gempackagetask spec Gem Specification new do s s version 0 1 0 s version 0 1 1 s author Scott Chacon commit 085bb3bcb608e1e8451d4b2432f8ecbe6306e7e7 Author Scott Chacon lt schacon gee mail com gt Date Sat Mar 15 16 40 33 2008 0700 removed unnecessary test code diff git a lib simplegit rb b lib simplegit
37. Chacon lt schacon geemail com gt selse Someo Nelse lt selse geemail com gt To get a list of the author names that SVN uses you can run this svn log xml grep author sort u perl pe s 1 That gives you the log output in XML format then it looks for the authors creates a unique list and then strips out the XML Obviously this only works on a machine with grep sort and perl installed Then redirect that output into your users txt file so you can add the equivalent Git user data next to each entry You can provide this file to git svn to help it map the author data more accurately You can also tell git svn not to include the metadata that Subversion normally imports by passing no metadata to the clone or init command This makes your import command look like this git svn clone http my project googlecode com svn authors file users txt no metadata s my project Now you should have a nicer Subversion import in your my project directory Instead of commits that look like this commit 37efa680e8473b615de980Fa935944215428a35a Author schacon schacon94c93b258 373f 11de be05 5f7a86268029 Date Sun May 3 00 12 22 2009 0000 fixed install go to trunk git svn id https my project googlecode com svn trunk 94 4c93b258 373f 11de be05 5f7a86268029 214 CHAPTER 8 GIT AND OTHER SYSTEMS they look like this commit 03a8785f44c8ea5cdb0e8834b7c8e6c469be2ff2 Author Scott Chacon lt sch
38. GETTING STARTED Nearly Every Operation Is Local Most operations in Git only need local files and resources to operate generally no informa tion is needed from another computer on your network If you re used to a CVCS where most operations have that network latency overhead this aspect of Git will make you think that the gods of speed have blessed Git with unworldly powers Because you have the entire history of the project right there on your local disk most operations seem almost instantaneous For example to browse the history of the project Git doesn t need to go out to the server to get the history and display it for you it simply reads it directly from your local database This means you see the project history almost instantly If you want to see the changes introduced between the current version of a file and the file a month ago Git can look up the file from a month ago and do a local difference calculation instead of having to either ask a remote server to do itor pull an older version of the file from the remote server to do it locally This also means that there is very little you can t do if you re offline or off VPN If you get on an airplane or a train and want to do a little work you can commit happily until you get to a network connection to upload If you go home and can t get your VPN client working prop erly you can still work In many other systems doing so is either impossible or painful In Perforce for example
39. Legal Code 0 0005 251 Contents auri don nets bk dns Meh ORL SAGARA Meade abode fen wee xv About the Author iiien a n een II Ie xvii About the Technical Reviewer 0 0 00 c ccc ccc ccc cece nee e cence eee eae xviii Acknowledgments 00 0000 cece cence beeen eet ssh haee ean xix hueso Xxi CHAPTER1 Getting Started ooooooooooeoeoeoeeeeeeeeuuuse 1 About Version Control 00 0 0 ccc ccc cc cence ence eens 1 Local Version Control Systems 00 ccc cece cece eee eens 2 Centralized Version Control SystemS 0 00 cece eee 3 Distributed Version Control Systems 0 cece eee eee ee 4 A Short History of Git 5 Git BASICS oce er ert ret m e Ret RR Re e a 5 Snapshots Not Differences 0 0 cece cee eee eae 6 Nearly Every Operation Is Local 000 0 cece cece aees 7 Git Has Integrity 0 aA 7 Git Generally Only Adds Data 00 0 cece eee eee 7 The Three Sfates neces 0e re SERRE ERO E aden Eei 8 Installifi lE oreet a bom RR PX MM EN br E owned Rite 9 Installing from SOUrCE 2 cee eee ees 9 Installing on Linux lssssssese eR 10 Installing on Mac 2 ccc eee eens 10 Installing on WindOWS 0 0 c ccc cece eee eee ees 11 First Time Git Setup 0 0 ccc ccc cece eee ene e eee 11 Your Identity 0 0 nonan anera ees 11 NOUP EGON PES 12
40. The references won t be the same on someone else s copy of the repository and right after you initially clone a repository you ll have an empty reflog because no activity has occurred yet in your repository Running git show HEAD 2 months ago will work only if you cloned the project at least two months ago if you cloned it five minutes ago you ll get no results Ancestry References The other main way to specify a commit is via its ancestry If you place a at the end of a refer ence Git resolves it to mean the parent of that commit Suppose you look at the history of your project git log pretty format h s graph 734713b fixed refs handling added gc auto updated tests d921970 Merge commit phedders rdocs I 35cfb2b Some rdoc changes 1coo2dd added some blame and merge stuff 1c36188 ignore gem 9b29157 add open3 detach to gemspec file list Then you can see the previous commit by specifying HEAD which means the parent of HEAD git show HEAD commit d921970aadf03b3cf0e71becdaab3147ba71cdef Merge 1c002dd 35cfb2b Author Scott Chacon schaconggmail com Date Thu Dec 11 15 08 43 2008 0800 Merge commit phedders rdocs CHAPTER 6 GIT TOOLS 147 You can also specify a number after the for example d921970 2 means the second parent of d921970 This syntax is only useful for merge commits which have more than one parent The first parent is the branch you we
41. When You Distribute or Publicly Perform the Work You may not impose any effective technological measures on the Work that restrict the ability of a recipient of the Work from You to exercise the rights granted to that recipient under the terms of the License This Section 4 a applies to the Work as incorporated in a Collection but this does not require the Collection apart from the Work itself to be made sub ject to the terms of this License If You create a Collection upon notice from any Licensor You must to the extent practicable remove from the Collection any credit as required by Section 4 d as requested If You create an Adaptation upon notice from any Licensor You must to the extent practicable remove from the Adaptation any credit as required by Section 4 d as requested b You may Distribute or Publicly Perform an Adaptation only under i the terms of this License ii a later version of this License with the same License Elements as this License iii a Creative Commons jurisdiction license either this or a later license version that contains the same License Elements as this License e g Attribution NonCommercial ShareAlike 3 0 US Applicable License You must include a copy of or the URI for Applicable License with every copy of each Adap tation You Distribute or Publicly Perform You may not offer or impose any terms on the Adaptation that restrict the terms of the Applicable License or the ability of the recipie
42. a reference in newer versions of Git you can run git remote rename to change a remote s shortname For instance if you want to rename pb to paul you can do so with git remote rename git remote rename pb paul git remote origin paul It s worth mentioning that this changes your remote branch names too What used to be referenced at pb master is now at paul master If you want to remove a reference for some reason you ve moved the server or are no longer using a particular mirror or perhaps a contributor isn t contributing anymore you can use git rm git remote rm paul git remote origin Tagging Like most VCSs Git has the ability to tag specific points in history as being important Generally people use this functionality to mark release points v1 0 and so on In this section you ll learn how to list the available tags how to create new tags and what the different types of tags are CHAPTER 2 GIT BASICS 39 Listing Your Tags Listing the available tags in Git is straightforward Just type git tag git tag v0 1 v1 3 This command lists the tags in alphabetical order the order in which they appear has no real importance You can also search for tags with a particular pattern The Git source repo for instance contains more than 240 tags If you re only interested in looking at the 1 4 2 series you can run this git tag 1 v1 4 2 V1 4 2 1 V1 4 2 2 V1 4 2 3 V1 4 2 4 Creating Tags Git uses tw
43. a single huge file every clone for all time will be forced to download that large file even if it was removed from the project in the very next commit Because it s reachable from the history it will always be there This can be a huge problem when you re converting Subversion or Perforce repositories into Git Because you don t download the whole history in those systems this type of addition carries few consequences If you did an import from another system or otherwise find that your repository is much larger than it should be here is how you can find and remove large objects Be warned this technique is destructive to your commit history It rewrites every commit object downstream from the earliest tree you have to modify to remove a large file reference If you do this immediately after an import before anyone has started to base work on the com mit you re fine otherwise you have to notify all contributors that they must rebase their work onto your new commits To demonstrate you ll add a large file into your test repository remove it in the next com mit find it and remove it permanently from the repository First add a large object to your history curl http kernel org pub software scm git git 1 6 3 1 tar bz2 git tbz2 git add git tbz2 git commit am added git tarball master 6df7640 added git tarball 1 files changed 0 insertions 0 deletions create mode 100644 git tbz2 248 CHAPTER 9 GIT INT
44. added cat file 310154e updated README formatting and added blame f7f3f6d changed my name a bit Notice the reverse order The interactive rebase gives you a script that it s going to run It will start at the commit you specify on the command line HEAD 3 and replay the changes introduced in each of these commits from top to bottom It lists the oldest at the top rather than the newest because that s the first one it will replay You need to edit the script so that it stops at the commit you want to edit To do so change the word pick to the word edit for each of the commits you want the script to stop after For example to modify only the third commit message you change the file to look like this edit f7f3f6d changed my name a bit pick 310154e updated README formatting and added blame pick a5f4a0d added cat file When you save and exit the editor Git rewinds you back to the last commit in that list and drops you on the command line with the following message git rebase i HEAD 3 Stopped at 7482e0d updated the gemspec to hopefully work better You can amend the commit now with git commit amend Once you re satisfied with your changes run git rebase continue These instructions tell you exactly what to do Type the following git commit amend Change the commit message and exit the editor Then run this git rebase continue This command will apply the other two commits automatically and then you re done If yo
45. admins have experience with them and many OS distributions are set up with them or have tools to manage them Next access over SSH is secure all data transfer is encrypted and authenticated Last like the Git and Local protocols SSH is efficient making the data as compact as possible before transferring it The Cons The negative aspect of SSH is that you can t serve anonymous access of your repository over it People must have access to your machine over SSH to access it even in a read only capac ity which doesn t make SSH access conducive to open source projects If you re using it only within your corporate network SSH may be the only protocol you need to deal with If you want to allow anonymous read only access to your projects you ll have to set up SSH for you to push over but something else for others to pull over The Git Protocol Next is the Git protocol This is a special daemon that comes packaged with Git it listens on a dedicated port 9418 that provides a service similar to the SSH protocol but with absolutely no authentication In order for a repository to be served over the Git protocol you must cre ate the git export daemon ok file the daemon won t serve a repository without that file in it but other than that there is no security Either the Git repository is available for everyone to clone or it isn t This means that there is generally no pushing over this protocol You can 82 CHAPTER 4 GIT ON THE SERVE
46. again and then pushes this back up to the server git commit am small tweak featureA ed774b3 small tweak 1 files changed 1 insertions 1 deletions git push origin featureA To jessica githost simplegit git 3300904 ed774b3 featureA gt featureA 122 CHAPTER 5 DISTRIBUTED GIT Jessica s commit history now looks something like Figure 5 13 origin featureA lt i 4b078 ledee 774b3 85127 cd685 origin featureBee Figure 5 13 Jessica s history after committing on a feature branch master gi K Jessica Josie and John inform the integrators that the featureA and featureBee branches on the server are ready for integration into the mainline After they integrate these branches into the mainline a fetch will bring down the new merge commits making the commit history look like Figure 5 14 origin featureA Figure 5 14 Jessica s history after merging both her topic branches master origin master j CHAPTER 5 DISTRIBUTED GIT 123 Many groups switch to Git because of this ability to have multiple teams working in paral lel merging the different lines of work late in the process The ability of smaller subgroups of a team to collaborate via remote branches without necessarily having to involve or impede the entire team is a huge benefit of Git The sequence for the workflow you saw here is something like Figure 5 15 Jessica John Josie S
47. am Adding git svn instructions to the README master 97031e5 Adding git svn instructions to the README 1 files changed 1 insertions 1 deletions Next you need to push your change upstream Notice how this changes the way you work with Subversion you can do several commits offline and then push them all at once to the Subversion server To push to a Subversion server you run the git svn dcommit command git svn dcommit Committing to file tmp test svn trunk M README txt Committed r79 M README txt 179 938b1a547c2cc92033b744d32030e86468294a5c8 trunk No changes between current HEAD and refs remotes trunk Resetting to the latest refs remotes trunk This takes all the commits you ve made on top of the Subversion server code does a Subversion commit for each and then rewrites your local Git commit to include a unique identifier This is important because it means that all the SHA 1 checksums for your commits change Partly for this reason working with Git based remote versions of your projects CHAPTER 8 GIT AND OTHER SYSTEMS 207 concurrently with a Subversion server isn t a good idea If you look at the last commit you can see the new git svn id that was added git log 1 commit 938b1a547c2cc92033b74d32030e86468294a5c8 Author schacon lt schacon 4c93b258 373f 11de be05 5f7a86268029 gt Date Sat May 2 22 06 44 2009 0000 Adding git svn instructions to the README git svn id file tmp test svn tr
48. another branch so you re not going to lose anything To see all the branches that contain work you haven t yet merged in you can run git branch no merged git branch no merged testing This shows your other branch Because it contains work that isn t merged in yet trying to delete it with git branch d will fail git branch d testing error The branch testing is not an ancestor of your current HEAD If you are sure you want to delete it run git branch D testing If you really do want to delete the branch and lose that work you can force it with D as the helpful message points out Branching Workflows Now that you have the basics of branching and merging down what can or should you do with them In this section I ll cover some common workflows that this lightweight branching makes possible so you can decide if you would like to incorporate it into your own develop ment cycle 62 CHAPTER 3 GIT BRANCHING Long Running Branches Because Git uses a simple three way merge merging from one branch into another multiple times over a long period is generally easy to do This means you can have several branches that are always open and that you use for different stages of your development cycle you can merge regularly from some of them into others Many Git developers have a workflow that embraces this approach such as having only code that is entirely stable in their master branch possibly only code that has bee
49. at a time and then push it back into another repository it s ridiculously inefficient but it s the only easy way to do this Getting Started Now that you have a Subversion repository to which you have write access you can go through a typical workflow You ll start with the git svn clone command which imports an entire Subversion repository into a local Git repository Remember that if you re importing from CHAPTER 8 GIT AND OTHER SYSTEMS 205 a real hosted Subversion repository you should replace the file tmp test svn here with the URL of your Subversion repository git svn clone file tmp test svn T trunk b branches t tags Initialized empty Git repository in Users schacon projects testsvnsync svn git I1 b4e387bc68740b5af56c2a5faf4003ae42bd135c trunk A m4 acx pthread m4 A m4 stl hash m4 175 d1957f3b307922124eec6314e15bcda59e3d9610 trunk Found possible branch point file tmp test svn trunk gt file tmp test svn branches my calc branch 75 Found branch parent my calc branch d1957f3b307922124eec6314e15bcda59e3d9610 Following parent with do switch Successfully followed parent 176 8624824eccObadd73f40ea2f01fce51894189b01 my calc branch Checked out HEAD file tmp test svn branches my calc branch r76 This runs the equivalent of two commands git svn init followed by git svn fetch on the URL you provide This can take a while The test project has only about 75 commits and the codeb
50. b lib simplegit rb index dd5ecc4 57399e0 100644 a lib simplegit rb b lib simplegit rb 22 7 22 7 class SimpleGit end def log treeish master command git log n 25 treeish command git log n 30 treeish end CHAPTER 6 GIT TOOLS 153 def blame path Stage this hunk y n a d j J g e You have a lot of options at this point Typing shows a list of what you can do Stage this hunk y n a d j J g e stage this hunk do not stage this hunk stage this and all the remaining hunks in the file do not stage this hunk nor any of the remaining hunks in the file select a hunk to go to search for a hunk matching the given regex leave this hunk undecided see next undecided hunk leave this hunk undecided see next hunk leave this hunk undecided see previous undecided hunk leave this hunk undecided see previous hunk split the current hunk into smaller hunks manually edit the current hunk print help w D oU XA CC NOAA 5 e 1 Generally you ll type y or n if you want to stage each hunk but staging all of them in cer tain files or skipping a hunk decision until later can be helpful too If you stage one part of the file and leave another part unstaged your status output will look like this What now 1 staged unstaged path 1 unchanged 0 1 TODO 1 1 nothing index html 1 1 4 0 lib simplegit rb The status of the simplegit rb file is interesting I
51. branch points to ca82a6d git show ca82a6dff817ec66F44342007202690a93763949 git show topici If you want to see which specific SHA a branch points to or if you want to see what any of these examples boils down to in terms of SHAs you can use a Git plumbing tool called rev parse You can see Chapter 9 for more information about plumbing tools basically rev parse exists for lower level operations and isn t designed to be used in day to day opera tions However it can be helpful sometimes when you need to see what s really going on Here you can run rev parse on your branch git rev parse topici ca82a6dff817ec66f44342007202690a93763949 RefLog Shortnames One ofthe things Git does in the background while you re working away is keep a reflog a log of where your HEAD and branch references have been for the last few months You can see your reflog by using git reflog git reflog 734713b HEAD O commit fixed refs handling added gc auto updated d921970 HEAD 1 merge phedders rdocs Merge made by recursive 1cOO2dd HEAD 2 commit added some blame and merge stuff 1c36188 HEAD 3 rebase i squash updating HEAD 95df984 HEAD 4 commit This is a combination of two commits 1c36188 HEAD 5 rebase i squash updating HEAD 7e05da5 HEAD 6 rebase i pick updating HEAD Every time your branch tip is updated for any reason Git stores that information for you in this temporary history And
52. can namespace them easily this way Pushing Refspecs It s nice that you can fetch namespaced references that way but how does the QA team get their branches into a qa namespace in the first place You accomplish that by using refspecs to push If the QA team wants to push their master branch to qa master on the remote server they can run git push origin master refs heads qa master 240 CHAPTER 9 GIT INTERNALS If they want Git to do that automatically each time they run git push origin they can add a push value to their config file remote origin url git github com schacon simplegit progit git fetch refs heads refs remotes origin push refs heads master refs heads qa master Again this will cause a git push origin to push the local master branch to the remote qa master branch by default Deleting References You can also use the refspec to delete references from the remote server by running something like this git push origin topic Because the refspec is lt src gt lt dst gt by leaving off the lt src gt part this basically says to make the topic branch on the remote nothing which deletes it Transfer Protocols Git can transfer data between two repositories in two major ways over HTTP and via the so called smart protocols used in the file ssh and git transports This section will quickly cover how these two main protocols operate The Dumb Protocol Git transport over HTTP
53. code at multiple points before integrating them These are some commonly used workflows that are possible with a distributed system like Git but you can see that many variations are possible to suit your particular real world work flow Now that you can I hope determine which workflow combination may work for you I ll cover some more specific examples of how to accomplish the main roles that make up the different flows 109 110 CHAPTER 5 DISTRIBUTED GIT developer public developer public developer public Figure 5 3 Benevolent dictator workflow Contributing to a Project You know what the different workflows are and you should have a pretty good grasp of funda mental Git usage In this section you ll learn about a few common patterns for contributing to a project The main difficulty with describing this process is that there are a huge number of varia tions on how it s done Because Git is very flexible people can and do work together in many ways and it s problematic to describe how you should contribute to a project every project is a bit different Some of the variables involved are active contributor size chosen workflow your commit access and possibly the external contribution method The first variable is active contributor size How many users are actively contributing code to this project and how often In many instances you ll have two or three developers with a few comm
54. diff program path old file old hex old mode new file new hex new mode Because you only want the old file and new file arguments you use the wrapper script to pass the ones you need cat usr local bin extDiff bin sh eq 7 amp amp usr local bin extMerge 2 5 180 CHAPTER 7 CUSTOMIZING GIT You also need to make sure these tools are executable sudo chmod x usr local bin extMerge sudo chmod x usr local bin extDiff Now you can set up your config file to use your custom merge resolution and diff tools This takes a number of custom settings merge tool to tell Git what strategy to use mergetool cmd to specify how to run the command mergetool trustExitCode to tell Git if the exit code of that program indicates a successful merge resolution or not and diff external to tell Git what command to run for diffs So either you can run four config commands git config global merge tool extMerge git config global mergetool extMerge cmd extMerge BASE LOCAL REMOTE MERGED git config global mergetool trustExitCode false git config global diff external extDiff or you can edit your gitconfig file to add these lines merge tool extMerge mergetool extMerge cmd extMerge BASE LOCAL REMOTE MERGED trustExitCode false diff external extDiff After all this is set if you run diff commands such as this git diff 32d1776b1 32d1776b1 Instead of
55. easy it is to take a Git repository create a bare version and place it on a server to which you and your collaborators have SSH access Now you re ready to collaborate on the same project It s important to note that this is literally all you need to do to run a useful Git server to which several people have access just add SSH able accounts on a server and stick a bare repository somewhere that all those users have read and write access to You re ready to go nothing else is needed In the next few sections you ll see how to expand to more sophisticated setups This discussion will include not having to create user accounts for each user adding public read access to repositories setting up web UIs using the Gitosis tool and more However keep in mind that to collaborate with a couple of people on a private project all you need is an SSH server and a bare repository CHAPTER 4 GIT ON THE SERVER 85 Small Setups If you re a small outfit or are just trying out Git in your organization and have only a few devel opers things can be simple for you One of the most complicated aspects of setting up a Git server is user management If you want some repositories to be read only to certain users and read write to others access and permissions can be a bit difficult to arrange SSH Access If you already have a server to which all your developers have SSH access it s generally easiest to set up your first repository there because you h
56. env ruby data STDIN read last date git log pretty format ad 1 puts data gsub Date Date last date to s All the script does is get the latest commit date from the git log command stick that into any Date strings it sees in stdin and print the results it should be simple to do in whatever language you re most comfortable in You can name this script expand date and put it in your path Now you need to set up a filter in Git call it dater and tell it to use your expand date filter to smudge the files on checkout You ll use a Perl expression to clean that up on commit git config filter dater smudge expand date git config filter dater clean perl pe s Date Date This Perl snippet strips out anything it sees in a Date string to get back to where you started Now that your filter is ready you can test it by setting up a file with your Date key word and then setting up a Git attribute for that file that engages the new filter CHAPTER 7 CUSTOMIZING GIT 189 echo Date gt date test txt echo date txt filter dater gt gt gitattributes If you commit those changes and check out the file again you see the keyword properly substituted git add date test txt gitattributes git commit m Testing date expansion in Git rm date test txt git checkout date test txt cat date test txt Date Tue Apr 21 07 26 52 2009 0700 You can see how
57. example everyone knows to a certain degree what everyone else on the project is doing Administrators have fine grained control over who can do what and it s far easier to administer a CVCS than it is to deal with local databases on every client However this setup also has some serious downsides The most obvious is the single point of failure that the centralized server represents If that server goes down for an hour then during that hour nobody can collaborate at all or save versioned changes to anything they re working on If the hard disk the central database is on becomes corrupted and proper backups haven t been kept you lose absolutely everything the entire history of the project except whatever single snapshots people happen to have on their local machines Local VCS systems suffer from this same problem whenever you have the entire history of the project in a single place you risk losing everything Computer A Central VCS Server Checkout Version Database Computer B Figure 1 2 Centralized version control diagram CHAPTER 1 GETTING STARTED Distributed Version Control Systems This is where Distributed Version Control Systems DVCSs step in In a DVCS such as Git Mercurial Bazaar or Darcs clients don t just check out the latest snapshot of the files they fully mirror the repository Thus if any server dies and these systems were collaborating via it any of the client repositories can be copied back up to t
58. f1 50 43 ad 20 a6 92 6a 1f 9a 3a schacon agadorlaptop local First it confirms where you want to save the key ssh id_rsa and then it asks twice for a passphrase which you can leave empty if you don t want to type a password when you use the key Now each user that does this has to send their public key to you or whoever is adminis trating the Git server assuming you re using an SSH server setup that requires public keys All they have to do is copy the contents ofthe pub file and e mail it The public keys look some thing like this cat ssh id rsa pub ssh rsa AAAAB3NzaC1yc2EAAAABIWwAAAQEAK1LOUpkDHr fHY17SbrmT IpNLTGK9T jom BWDSU GP1 nafzlHDTYW7hd14yZ5ew18JH4IW9jbhUFrvidzM7xlELEVf4h9lFX5OVkbPppSwg0cda3 Pbv7k0dJ MTyBlWXFCR2HAo3FXRitBqxiX1nKhXpHAZsMciLq8V6R sNAQwds dMFvS1VK 7XA t3FaoJoAsncM109x5 3VOWw68 e1Fmbi1zuUFljOJKprrX88XypNDv jYNby6vw PbOrwert En mZ AW40ZPnTPI89ZPmVMLuayrD2cE86Z il8b gw3r3 1nKatm1kjn2so1d010raT IMqVSsbx NrRFi9wrf4M70 schacon agadorlaptop local For a more in depth tutorial on creating an SSH key on multiple operating systems see the GitHub guide on SSH keys at http github com guides providing your ssh key Setting Up the Server Let s walk through setting up SSH access on the server side In this example you ll use the authorized keys method for authenticating your users I also assume you re running a stan dard Linux distribution like Ubuntu First you create a git user and a ssh directory
59. for dealing with several very dif ferent types of Git projects you re likely to encounter and introduced a couple of new tools to help you manage this process Next you ll see how to work the other side of the coin main taining a Git project You ll learn how to be a benevolent dictator or integration manager 130 CHAPTER 5 DISTRIBUTED GIT Maintaining a Project In addition to knowing how to effectively contribute to a project you ll likely need to know how to maintain one This can consist of accepting and applying patches generated via format patch and e mailed to you or integrating changes in remote branches for repositories you ve added as remotes to your project Whether you maintain a canonical repository or want to help by verifying or approving patches you need to know how to accept work in a way that is clearest for other contributors and sustainable by you over the long run Working in Topic Branches When you re thinking of integrating new work it s generally a good idea to try it out in a topic branch a temporary branch specifically made to try out that new work This way it s easy to tweak a patch individually and leave it if it s not working until you have time to come back to it If you create a simple branch name based on the theme of the work you re going to try such as ruby client or something similarly descriptive you can easily remember it if you have to abandon it for a while and come back later The maintainer o
60. for each command using git config Here are a couple of examples you may want to set up git config global alias co checkout git config global alias br branch git config global alias ci commit git config global alias st status This means that for example instead of typing git commit you just need to type git ci As you go on using Git you ll probably use other commands frequently as well in this case don t hesitate to create new aliases This technique can also be very useful in creating commands that you think should exist For example to correct the usability problem you encountered with unstaging a file you can add your own unstage alias to Git git config global alias unstage reset HEAD This makes the following two commands equivalent git unstage fileA git reset HEAD fileA This seems a bit clearer It s also common to add a last command like this git config global alias last log 1 HEAD CHAPTER 2 GIT BASICS 45 This way you can see the last commit easily git last commit 66938dae3329c7aebe598c2246a8e6af90d04646 Author Josh Goebel lt dreamer3 gee mail com gt Date Tue Aug 26 19 48 51 2008 0800 test for current head Signed off by Scott Chacon lt schacon gee mail com gt As you can tell Git simply replaces the new command with whatever you alias it for How ever maybe you want to run an external command rather than a Git subcommand In that case you start the com
61. for that user sudo adduser git su git cd mkdir ssh CHAPTER 4 GIT ON THE SERVER 87 Next you need to add some developer SSH public keys to the authorized_keys file for that user Let s assume you ve received a few keys by e mail and saved them to temporary files Again the public keys look something like this cat tmp id_rsa john pub ssh rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQCB007n ww ouN4gSLKssMxXnBOvf9LGt4L ojG6rs6hPB09j9R T17 x41hJAOF3FR1rP6kYBRsWj2aThGw6HXLm9 5zytK6Ztg3RPKK 4k Yjh6541NYsnEAZUuXzOj TTyAUfrtU3Z5E003C40x0j6HOrfIF1kKI9MAQLMdpGWi1GYEIgS9Ez Sdfd8AcClicTDWbqLAcUAUpkaX8KyGlLwsNuuGztobF8m72ALC nLF6J LtPofwFBlgce myiv 07TCUSBdLOl1gMVOFqi1I2uPWOOKOWOAHukEOmf jy2j ctxSDBO220ymjaNsHTAkgtZg2AYYgPq dAv8JggJICUvax2T9va5 gsg keypair You append them to your authorized keys file cat tmp id rsa john pub ssh authorized keys cat tmp id rsa josie pub gt gt ssh authorized keys cat tmp id rsa jessica pub gt gt ssh authorized keys Now you can set up an empty repository for them by running git init with the bare option which initializes the repository without a working directory cd opt git mkdir project git cd project git git bare init Then John Josie or Jessica can push the first version of their project into that repository by adding it as a remote and pushing up a branch Note that someone must shell onto the machine and create a bare repository every time you want t
62. get a diff between what you have in your rack subdirectory and the code in your rack branch branch to see if you need to merge them you can t use the normal diff command Instead you must run git diff tree with the branch you want to compare to git diff tree p rack branch Or to compare what is in your rack subdirectory with what the master branch on the server was the last time you fetched you can run the following git diff tree p rack remote master CHAPTER 6 GIT TOOLS 173 Summary You ve seen a number of advanced tools that allow you to manipulate your commits and stag ing area more precisely When you notice issues you should be able to easily figure out what commit introduced them when and by whom If you want to use subprojects in your project you ve learned a few ways to accommodate those needs At this point you should be able to do most of the things in Git that you ll need on the command line day to day and feel comfort able doing so CHAPTER 7 Customizing Git S far I ve covered the basics of how Git works and how to use it and I ve introduced a num ber of tools that Git provides to help you use it easily and efficiently In this chapter I ll go through some operations that you can use to make Git operate in a more customized fashion by introducing several important configuration settings and the hooks system With these tools it s easy to get Git to work exactly the way you your company or your
63. git cat file commit rev sed 1 d if regex match message puts POLICY Your message is not formatted correctly exit 1 end end end check message format Putting that in your update script will reject updates that contain commits that have mes sages that don t adhere to your rule Enforcing a User Based ACL System Suppose you want to add a mechanism that uses an access control list ACL that specifies which users are allowed to push changes to which parts of your projects Some people have full access and others only have access to push changes to certain subdirectories or specific files To enforce this you ll write those rules to a file named acl that lives in your bare Git repository on the server You ll have the update hook look at those rules see what files are being introduced for all the commits being pushed and determine whether the user doing the push has access to update all those files The first thing you ll do is write your ACL Here you ll use a format very much like the CVS ACL mechanism it uses a series of lines where the first field is avail or unavail the next field is a comma delimited list of the users to which the rule applies and the last field is the path to which the rule applies blank meaning open access All of these fields are delimited by a pipe character In this case you have a couple of administrators some documentation writers with access to the doc directory and one developer who
64. how to handle those files For instance some text files may be machine generated and not diffable whereas some binary files can be diffed you ll see how to tell Git which is which Identifying Binary Files Some files look like text files but for all intents and purposes are to be treated as binary data For instance Xcode projects on the Mac contain a file that ends in pbxproj which is basically a JSON plain text JavaScript data format dataset written out to disk by the IDE that records your build settings and so on Although it s technically a text file because it s all ASCII you don t want to treat it as such because it s really a lightweight database you can t merge the contents if two people changed it and diffs generally aren t helpful The file is meant to be consumed by a machine In essence you want to treat it like a binary file To tell Git to treat all pbxproj files as binary data add the following line to your gitattributes file pbxproj crlf diff Now Git won t try to convert or fix CRLF issues nor will it try to compute or print a diff for changes in this file when you run git show or git diff on your project In the 1 6 series of Git you can also use a macro that is provided that means crlf diff pbxproj binary Diffing Binary Files In the 1 6 series of Git you can use the Git attributes functionality to effectively diff binary files You do this by telling Git how to convert your binary data to a
65. in benchmarks rb before you commit it You open it again and make that change and you re ready to commit However let s run git status one more time vim benchmarks rb git status On branch master Changes to be committed use git reset HEAD lt file gt to unstage new file README modified benchmarks rb Changed but not updated use git add file to update what will be committed modified benchmarks rb He Gt it it it it it He HE What the heck Now benchmarks rb is listed as both staged and unstaged How is that possible It turns out that Git stages a file exactly as itis when you run the git add command If you commit now the version of benchmarks rb as it was when you last ran the git add com mand is how it will go into the commit not the version of the file as it looks in your working directory when you run git commit If you modify a file after you run git add you have to run git add again to stage the latest version of the file git add benchmarks rb git status On branch master Changes to be committed use git reset HEAD lt file gt to unstage i 20 CHAPTER 2 GIT BASICS new file README modified benchmarks rb Ignoring Files Often you ll have a class of files that you don t want Git to automatically add or even show you as being untracked These are generally automatically generated files such as log files or files produced by your bu
66. include this code from a shared library like a CPAN install or Ruby gem or copy the source code into your own project tree The issue with including the library is that it s diffi cult to customize the library in any way and often more difficult to deploy it because you need to make sure every client has that library available The issue with vendoring the code into your own project is that any custom changes you make are difficult to merge when upstream changes become available Git addresses this issue using submodules Submodules allow you to keep a Git repository as a subdirectory of another Git repository This lets you clone another repository into your project and keep your commits separate Starting with Submodules Suppose you want to add the Rack library a Ruby web server gateway interface to your proj ect possibly maintain your own changes to it but continue to merge in upstream changes The first thing you should do is clone the external repository into your subdirectory You add external projects as submodules with the git submodule add command git submodule add git github com chneukirchen rack git rack Initialized empty Git repository in opt subtest rack git remote Counting objects 3181 done remote Compressing objects 100 1534 1534 done remote Total 3181 delta 1951 reused 2623 delta 1603 Receiving objects 100 3181 3181 675 42 KiB 422 KiB s done Resolving deltas 100 1951 1951 done Now
67. is a subdirectory in your working directory Git sees it as a submodule and doesn t track its contents when you re not in that directory Instead Git records it as a particu lar commit from that repository When you make changes and commit in that subdirectory the superproject notices that the HEAD there has changed and records the exact commit you re currently working off of that way when others clone this project they can re create the envi ronment exactly This is an important point with submodules you record them as the exact commit they re at You can t record a submodule at master or some other symbolic reference When you commit you see something like this git commit m first commit with submodule rack master 0550271 first commit with submodule rack 2 files changed 4 insertions 0 deletions create mode 100644 gitmodules create mode 160000 rack Notice the 160000 mode for the rack entry That is a special mode in Git that basically means you re recording a commit as a directory entry rather than a subdirectory or a file You can treat the rack directory as a separate project and then update your superproject from time to time with a pointer to the latest commit in that subproject All the Git commands work independently in the two directories git log 1 commit 0550271328a0038865aad6331e620cd7238601bb Author Scott Chacon lt schacon gmail com gt Date Thu Apr 9 09 03 56 2009 0700 CHAPTER 6 GIT TOOLS 167
68. it does then it was introduced sometime before this middle commit if it doesn t then the problem was 164 CHAPTER 6 GIT TOOLS introduced sometime after the middle commit It turns out there is no issue here and you tell Git that by typing git bisect good and continue your journey git bisect good Bisecting 3 revisions left to test after this b047b02ea83310a70fd603dc8cd7a6cd13d15c04 secure this thing Now you re on another commit halfway between the one you just tested and your bad commit You run your test again and find that this commit is broken so you tell Git that with git bisect bad git bisect bad Bisecting 1 revisions left to test after this f71ce38690acf49c1f3c9bea38e09d82a5ce6014 drop exceptions table This commit is fine and now Git has all the information it needs to determine where the issue was introduced It tells you the SHA 1 of the first bad commit and shows some of the commit information and which files were modified in that commit so you can figure out what happened that may have introduced this bug git bisect good b047b02ea83310a70Fd603dc8cd7a6cd13d15c04 is first bad commit commit b047b02ea83310a70fd603dc8cd7a6cd13d15c04 Author PJ Hyett lt pjhyett example com gt Date Tue Jan 27 14 48 32 2009 0800 secure this thing 040000 040000 40ee3e7821b895e52c1695092db9bdc4c614d1730 f24d3c6ebcfc639b1a3814550e62d60b8e68a8e4 M config When you re finished you should rungit bisect reset to reset you
69. key id gt Now you can sign tags without having to specify your key every time with the git tag command git tag s lt tag name gt 178 CHAPTER 7 CUSTOMIZING GIT core excludesfile You can put patterns in your project s gitignore file to have Git not see them as untracked files or try to stage them when you run git add on them as discussed in Chapter 2 However if you want another file outside of your project to hold those values or have extra values you can tell Git where that file is with the core excludesfile setting Simply set it to the path of a file that has content similar to what a gitignore file would have help autocorrect This option is available only in Git 1 6 1 and later If you mistype a command in Git 1 6 it shows you something like this git com git com is not a git command See git help Did you mean this commit If you set help autocorrect to 1 Git will automatically run the command if it has only one match under this scenario Colors in Git Git can color its output to your terminal which can help you visually parse the output quickly and easily A number of options can help you set the coloring to your preference color ui Git automatically colors most of its output if you ask it to You can get very specific about what you want colored and how but to turn on all the default terminal coloring set color ui to true git config global color ui true When that value is
70. ll use the normal path here because doing so is almost always faster To add a local repository to an existing Git project you can run something like this git remote add local proj opt git project git Then you can push to and pull from that remote as though you were doing so over a network The Pros The pros of file based repositories are that they re simple and they use existing file permis sions and network access If you already have a shared filesystem to which your whole team has access setting up a repository is very easy You stick the bare repository copy somewhere everyone has shared access to and set the read write permissions as you would for any other shared directory I ll discuss how to export a bare repository copy for this purpose in the next section Getting Git on a Server This is also a nice option for quickly grabbing work from someone else s working reposi tory If you and a co worker are working on the same project and they want you to check something out running a command like git pull home john project is often easier than them pushing to a remote server and you pulling down The Cons The cons of this method are that shared access is generally more difficult to set up and reach from multiple locations than basic network access If you want to push from your laptop when you re at home you have to mount the remote disk which can be difficult and slow compared to network based access CHAPTER 4 GIT ON
71. lt schacon example com gt Date Sun May 3 12 57 39 2009 0700 imported from current commit 7e519590de754d079dd73b44d695a42c9d2df452 Author Scott Chacon lt schacon example com gt Date Tue Feb 3 01 00 00 2009 0700 imported from back 2009 02 03 CHAPTER 8 GIT AND OTHER SYSTEMS 221 There you go a nice clean Git repository It s important to note that nothing is checked out you don t have any files in your working directory at first To get them you must reset your branch to where master is now 1s git reset hard master HEAD is now at 10bfe7d imported from current Is file rb lib You can do alot more with the fast import tool handle different modes binary data multiple branches and merging tags progress indicators and more A number of examples of more complex scenarios are available in the contrib fast import directory of the Git source code one of the better ones is the git p4 script I just covered Summary You should feel comfortable using Git with Subversion or importing nearly any existing reposi tory into a new Git one without losing data The next chapter will cover the raw internals of Git so you can craft every single byte if need be CHAPTER 9 Git Internals Ys may have skipped to this chapter from a previous chapter or you may have gotten here after reading the rest of the book in either case this is where you ll go over the inner work ings and implementation of Git I found th
72. merge base for branch merging master OE cs iss53 Figure 3 17 Git automatically creates a new commit object that contains the merged work Basic Merge Conflicts Occasionally this process doesn t go smoothly If you changed the same part of the same file differently in the two branches you re merging together Git won t be able to merge them cleanly If your fix for issue 53 modified the same part of a file as the hotfix you get a merge conflict that looks something like this git merge iss53 Auto merging index html CONFLICT content Merge conflict in index html Automatic merge failed fix conflicts and then commit the result Git hasn t automatically created a new merge commit It has paused the process while you resolve the conflict If you want to see which files are unmerged at any point after a merge con flict you can run git status CHAPTER 3 GIT BRANCHING 59 master git status index html needs merge On branch master Changed but not updated use git add lt file gt to update what will be committed use git checkout file to discard changes in working directory unmerged index html Anything that has merge conflicts and hasn t been resolved is listed as unmerged Git adds standard conflict resolution markers to the files that have conflicts so you can open them manually and resolve those conflicts Your file contains a section
73. only has access to the lib and tests directories and your ACL file looks like this avail nickh pjhyett defunkt tpw avail usinclair cdickens ebronte doc avail schacon lib avail schacon tests You begin by reading this data into a structure that you can use In this case to keep the example simple you ll only enforce the avail directives Here is a method that gives you an associative array where the key is the user name and the value is an array of paths to which the user has write access def get acl access data acl file read in ACL data acl file File read acl file split n reject line line access acl file each do line avail users path line split next unless avail avail users split each do user 196 CHAPTER 7 CUSTOMIZING GIT access user access user lt lt path end end access end On the ACL file you looked at earlier this get acl access data method returns a data structure that looks like this defunkt gt nil tpw gt nil nickh gt nil pjhyett nil schacon lib tests cdickens doc usinclair doc ebronte gt doc Now that you have the permissions sorted out you need to determine what paths the commits being pushed have modified so you can make sure the user who s pushing has access to all of them You can pretty easily see what files have been modified in a single commit with the name o
74. opera instead of something useful Remember that although you re using git merge to do this operation and the merge likely will be much easier than it would be in Subversion because Git will automatically detect the appropriate merge base for you this isn t a normal Git merge commit You have to push this data back to a Subversion server that can t handle a commit that tracks more than one par ent so after you push it up it will look like a single commit that squashed in all the work of another branch under a single commit After you merge one branch into another you can t easily go back and continue working on that branch as you normally can in Git The dcommit command that you run erases any information that says what branch was merged in so sub sequent merge base calculations will be wrong the dcommit makes your git merge result look like youran git merge squash Unfortunately there s no good way to avoid this situation Subversion can t store this information so you ll always be crippled by its limitations while you re using it as your server To avoid issues you should delete the local branch in this case opera after you merge it into trunk Subversion Commands The git svn toolset provides a number of commands to help ease the transition to Git by providing some functionality that s similar to what you had in Subversion Here are a few com mands that give you what Subversion used to SVN Style History If you re used t
75. or what have you The Your Clone URL is a read write SSH based URL that you can read or write over only if you connect with the SSH private key associated with the public key you uploaded for your user When other users visit this project page they won t see that URL only the public one Importing from Subversion If you have an existing public Subversion project that you want to import into Git GitHub can often do that for you At the bottom of the instructions page is a link to a Subversion import If you click it you see a form with information about the import process and a text box where you can paste in the URL of your public Subversion project see Figure 4 9 Import a Subversion Repository Read Before Proceeding The import process could take as little as 5 minutes to as long as 5 days depending on the size of your repository This has everything to do with how slow subversion is but we re working on speeding up the process If your subversion repository contains a non standard directory structure this import process will probably not work for you Check out our Guide for running the import yourself This service currently only supports public subversion repositories Project Name iphone project SVN Repository URL Step 1 Import Authors Figure 4 9 Subversion importing interface If your project is very large nonstandard or private this process probably won t work for you
76. process 243 244 file annotation 162 163 file based repositories 80 files checking status of 17 18 committing changes to 23 24 ignoring 20 lifecycle of status of 17 moving 25 26 removing 24 25 removing from commits 161 staging modified 18 19 staging and unstaging 150 152 tracked 16 tracking new 18 undoing changes to 32 34 unstaging 33 34 untracked 16 18 viewing staged and unstaged changes 20 23 FileUtils mkdir pO function 231 filter attribute 187 filter branch command 160 162 format option 29 30 format patch command 127 132 formatting 181 182 Freenode IRC server 13 fsck utility 247 G garbage collection 244 gc command 237 244 245 get acl access data method 196 Git basics 5 9 compared with other VCSs 6 configuration 11 176 183 data model 227 data storage in 6 7 help 13 history of 5 hosted 96 105 installation 9 11 local operations in 7 migrating to 212 221 setup of 11 12 states 8 9 Subversion and 203 212 INDEX 261 user interface 223 Git attributes See attributes gitattributes file 184 187 git channel 13 gitconfig file 11 175 Git daemon 95 96 Git data model 227 git directory 8 223 224 Git enforced policy example 193 201 git export daemon ok file 81 git fsck utility 247 githib channel 13 Git hooks See hooks GitHub 97 105 108 adding collaborators 102 creating new repository 99 101 forking projects 104 importing from Subversion 101 main
77. project page 103 setting up user account on 97 gitignore file 20 25 gitk program 31 Gitosis 91 96 gitosis conf file 93 gitosis init command 92 Git projects See projects Git protocol 81 82 95 96 git reflog tool 246 git remote add command 36 65 238 Git repositories See repositories Git server generating SSH public key 85 86 network protocols 79 83 public access to 88 89 running 79 setting up 83 84 small setups 85 91 SSH access 85 88 git shell tool 88 git svn tool 203 212 branching issues 208 209 clone command 204 205 dcommit command 206 208 fetch command 208 getting started 204 206 pulling in new changes 207 208 rebase command 207 208 setting up 204 summary 212 Git tools debugging 162 164 interactive staging 150 153 revising commit history 156 162 revision selection 143 149 stashing 153 156 submodules 165 171 subtree merging 171 172 262 INDEX GitWeb 90 91 glob patterns 20 global option 12 175 GNU Privacy Guard GPG 39 grep option 31 H hash object command 140 225 HEAD file 145 169 224 233 234 HEAD pointer 50 52 help autocorrect setting 178 help sources 13 hooks client side 190 192 199 201 committing workflow 191 e mail workflow 191 installing 190 server side 190 199 hooks directory 224 hosted Git 96 105 hotfix branch 55 http fetch process 240 HTTP protocol 82 83 240 242 HTTPS protocol 82 83 ignore unmatch option 249 import
78. rewrite huge swaths of your history so you probably shouldn t use it unless your project isn t yet public and other people haven t based work off the commits you re about to rewrite However it can be CHAPTER 6 GIT TOOLS 161 very useful You ll learn a few of the common uses so you can get an idea of some of the things it s capable of Removing a File from Every Commit This occurs fairly commonly Someone accidentally commits a huge binary file with a thought less git add and you want to remove it everywhere Perhaps you accidentally committed a file that contained a password and you want to make your project open source filter branch is the tool you probably want to use to scrub your entire history To remove a file named passwords txt from your entire history you can use the tree filter option to filter branch git filter branch tree filter rm f passwords txt HEAD Rewrite 6b9b3cf04e7c5686a9cb838c3f36a8cb6aofc2bd 21 21 Ref refs heads master was rewritten The tree filter option runs the specified command after each checkout of the project and then recommits the results In this case you remove a file called passwords txt from every snapshot whether it exists or not If you want to remove all accidentally committed editor backup files you can run something like git filter branch tree filter rm f HEAD You ll be able to watch Git rewriting trees and commits and then move the branch pointer at the end It
79. shortlogs 142 small public 124 126 superprojects 169 tagging releases 140 141 working in topic branches 130 proposed pu branches 63 INDEX 263 protocols Git 81 82 95 96 HTTP S 82 83 240 242 Local 80 81 network 79 83 SSH 81 public access 88 89 Public Clone URL 101 public key SSH 85 86 public projects large 127 129 small 124 126 pull command 36 133 pull requests 124 push command 37 43 push origin command 240 Python setuptools 92 Q question mark 2 20 R ranges of commits 147 149 rcs command 2 rebase command 70 139 157 158 rebasing 70 76 receive denyDeletes setting 183 197 receive denyNonFastForwards setting 183 197 receive fsckObjects setting 183 receive pack process 242 243 recursive strategy 171 references refs 232 235 ancestry 147 branch 145 deleting 240 HEAD file and 233 234 remote 235 tag 234 235 reflogs 145 146 246 247 reflog tool 246 refs directory 224 refspecs 238 239 refs remotes directory 235 releases preparing 141 tagging 140 141 remote command 35 remote add command 36 65 238 remote rename command 38 remote show command 37 38 remote branches 64 65 68 69 checking out 133 deleting 69 pushing 68 69 remote references 235 INDEX remote repositories 79 adding 36 displaying 35 getting data from 36 inspecting 37 38 pushing to 37 removing 38 renaming 38 working with 35 38 repositories bare 79 84 cloni
80. single checkout of one version of the project These files are pulled out of the compressed database in the Git directory and placed on disk for you to use or modify The staging area is a simple file generally contained in your Git directory that stores information about what will go into your next commit It s sometimes referred to as the index but it s becoming standard to refer to it as the staging area The basic Git workflow goes something like this 1 You modify files in your working directory 2 You stage the files adding snapshots of them to your staging area CHAPTER 1 GETTING STARTED 3 You do a commit which takes the files as they are in the staging area and stores that snapshot permanently to your Git directory If a particular version of a file is in the Git directory it s considered committed If it s modified but has been added to the staging area it is staged And if it was changed since it was checked out but has not been staged it is modified In Chapter 2 you ll learn more about these states and how you can either take advantage of them or skip the staged part entirely Installing Git Let s get into using some Git First things first you have to install it You can get it a number of ways the two major ones are to install it from source or to install an existing package for your platform Installing from Source If you can it s generally useful to install Git from source because you ll get the m
81. that looks something like this lt lt lt lt lt lt lt HEAD index html lt div id footer contact email support github com lt div gt lt div id footer gt please contact us at support github com lt div gt iss53 index html This means the version in HEAD your master branch because that was what you had checked out when you ran your merge command is the top part of that block everything above the whereas the version in your 15553 branch looks like everything in the bot tom part In order to resolve the conflict you have to either choose one side or the other or merge the contents yourself For instance you might resolve this conflict by replacing the entire block with this div id footer please contact us at email support github com div This resolution has a little of each section and I ve fully removed the and lines After you ve resolved each of these sections in each conflicted file run git add on each file to mark it as resolved Staging the file marks it as resolved in Git If you want to use a graphical tool to resolve these issues you can run git mergetool which fires up an appropriate visual merge tool and walks you through the conflicts git mergetool merge tool candidates kdiff3 tkdiff xxdiff meld gvimdiff opendiff emerge vimdiff Merging the files index html Normal merge conflict for index html local modified
82. that you have Git on your system you ll want to do a few things to customize your Git environment You should have to do these things only once they ll stick around between upgrades You can also change them at any time by running through the commands again Git comes with a tool called git config that lets you get and set configuration variables that control all aspects of how Git looks and operates These variables can be stored in three different places etc gitconfig file Contains values for every user on the system and all their reposi tories If you pass the option systemto git config it reads and writes from this file specifically e gitconfig file Specific to your user You can make Git read and write to this file specifically by passing the global option e config file in the git directory that is git config of whatever repository you re currently using Specific to that single repository Each level overrides values in the previous level so values in git config trump those in etc gitconfig On Windows systems Git looks for the gitconfig file in the HOME directory C Documents and Settings V USER for most people It also still looks for etc gitconfig although it s rela tive to the MSys root which is wherever you decide to install Git on your Windows system when you run the installer Your Identity The first thing you should do when you install Git is to set your username and e mail address This is im
83. the event that the Licensor is a member of a col lecting society that administers voluntary licensing schemes via that society from any exercise by You of the rights granted under this License that is for a purpose or use which is otherwise than noncommercial as permitted under Section 4 c 256 APPENDIX CREATIVE COMMONS LEGAL CODE f Except as otherwise agreed in writing by the Licensor or as may be otherwise per mitted by applicable law if You Reproduce Distribute or Publicly Perform the Work either by itself or as part of any Adaptations or Collections You must not distort mutilate modify or take other derogatory action in relation to the Work which would be prejudicial to the Original Author s honor or reputation Licensor agrees that in those jurisdictions e g Japan in which any exercise of the right granted in Section 3 b of this License the right to make Adaptations would be deemed to be a distortion mutilation modification or other derogatory action prejudicial to the Original Author s honor and reputation the Licensor will waive or not assert as appropriate this Section to the fullest extent permitted by the applicable national law to enable You to reasonably exercise Your right under Section 3 b of this License right to make Adaptations but not otherwise 5 Representations Warranties and Disclaimer UNLESS OTHERWISE MUTUALLY AGREED TO BY THE PARTIES IN WRITING AND TO THE FULLEST EXTENT PERMITTED BY APPLICA
84. the refs heads part in detail in Chapter 9 but you can generally leave it off You can also do git push origin serverfix serverfix which does the same thing it says Take my serverfix and make it the remote s serverfix You can use this format to push a local branch into a remote branch that is named differently If you didn t want it to be called serverfix on the remote you could instead run git push origin serverfix awesomebranch to push your serverfix branch to the awesomebranch branch on the remote project The next time one of your collaborators fetches from the server they will get a reference to where the server s version of serverfixis under the remote branch origin serverfix git fetch origin remote Counting objects 20 done remote Compressing objects 100 14 14 done remote Total 15 delta 5 reused O delta 0 Unpacking objects 100 15 15 done From git github com schacon simplegit new branch serverfix origin serverfix It s important to note that when you do a fetch that brings down new remote branches you don t automatically have local editable copies of them In other words in this case you don t have a new serverfix branch you only have an origin serverfix pointer that you can t modify To merge this work into your current working branch you can run git merge origin serverfix If you want your own serverfix branch that you can work on you can base it off your remote branch git checkou
85. tmp test svn trunk at 187 to file tmp test svn branches opera Found possible branch point file tmp test svn trunk gt file tmp test svn branches opera 87 Found branch parent opera 1f6bfe471083cbca06ac8d4176f7ad4de0d62e5f Following parent with do switch Successfully followed parent r89 9b6feob90c5c9adf9165f700897518dbc54a7cbf opera 210 CHAPTER 8 GIT AND OTHER SYSTEMS This does the equivalent of the svn copy trunk branches opera command in Subversion and operates on the Subversion server It s important to note that it doesn t check you out into that branch if you commit at this point that commit will go to trunk on the server not opera Switching Active Branches Git figures out what branch your dcommits go to by looking for the tip of any of your Subver sion branches in your history you should have only one and it should be the last one with a git svn id in your current branch history If you want to work on more than one branch simultaneously you can set up local branches to dcommit to specific Subversion branches by starting them at the imported Sub version commit for that branch If you want an opera branch that you can work on separately you can run git branch opera remotes opera Now if you want to merge your opera branch into trunk your master branch you can do so with a normal git merge But you need to provide a descriptive commit message via m or the merge will say Merge branch
86. to daemonize the process Tl cover this option in the next section if you prefer that route 90 CHAPTER 4 GIT ON THE SERVER GitWeb Now that you have basic read write and read only access to your project you may want to set up a simple web based visualizer Git comes with a CGI script called GitWeb that is commonly used for this You can see GitWeb in use at sites like http git kernel org see Figure 4 1 pub scm git git git summary Tt eii summary shortiog log commit commitdiff tree commit WR seach description The core git plumbing owner Junio C Hamano last change Fri 20 Feb 2009 07 44 07 0000 URL git git kernel org pub scmgit git git http www kernel org pub scm git git git shortlog 33 hours ago Junio C Hamano Merge branch maint mastor commis eommadit tree snapshot 34 hours ago Matthieu Moy More friendly message when locking the index fails maint commi comma ree snapshot 34 hours ago Matthieu Moy Document git blame reverse commit coment irog snapshot 34 hours ago Marcel M Cary gitweb Hyperlink multiple git hashes on the same commi comms comm ree soapsnot 34 hours ago Johannes Schindelin system path simplify using strip path suffix commit commandi tree snapshot 34 hours ago Johannes Schindelin Introduce the function strip path suffix Commit commadi tree snapsnot 2daysago Todd Zullinger Documentation Note file formats send email accepts
87. tool and in what cases you won t want to use it The Basic Rebase If you go back to an earlier example from the Basic Branching and Merging section see Figure 3 27 you can see that you diverged your work and made commits on two different branches experiment 3 master 1e HI Figure 3 27 Your initial diverged commit history The easiest way to integrate the branches as I ve already covered is the merge command It performs a three way merge between the two latest branch snapshots C3 and C4 and the most recent common ancestor of the two C2 creating a new snapshot and commit as shown in Figure 3 28 Figure 3 28 Merging a branch to integrate the diverged work history However there is another way you can take the patch of the change that was introduced in C3 and reapply it on top of C4 In Git this is called rebasing With the rebase command you can take all the changes that were committed on one branch and replay them on another one CHAPTER 3 GIT BRANCHING 71 In this example you d run the following git checkout experiment git rebase master First rewinding head to replay your work on top of it Applying added staged command It works by going to the common ancestor of the two branches the one you re on and the one you re rebasing onto getting the diff introduced by each commit of the branch you re on saving those diffs to temporary files resetting the curr
88. transport new Ajax Request main chronic value out innerHTML transport responseText method get onSuccess function transport IE out innerH7ML transport responseText n k script A lt body gt lt script gt Y ES yaly Figure 7 1 P4Merge Formatting and Whitespace Formatting and whitespace issues are some of the more frustrating and subtle problems that many developers encounter when collaborating especially cross platform It s very easy for patches or other collaborated work to introduce subtle whitespace changes because editors silently introduce them or Windows programmers add carriage returns at the end of lines they touch in cross platform projects Git has a few configuration options to help with these issues core autocrlf If you re programming on Windows or using another system but working with people who are programming on Windows you ll probably run into line ending issues at some point This is because Windows uses both a carriage return character and a linefeed character for newlines in its files whereas Mac and Linux systems use only the linefeed character This is a subtle but incredibly annoying fact of cross platform work Git can handle this by auto converting CRLF line endings into LF when you commit and vice versa when it checks out code onto your filesystem You can turn on this functionality 181 182 CHAPTER 7 CUSTOMIZING GIT with the core autocrlf settin
89. ve created merged and deleted some branches let s look at some branch management tools that will come in handy when you begin using branches all the time The git branch command does more than just create and delete branches If you run it with no arguments you get a simple listing of your current branches git branch iss53 master testing CHAPTER 3 GIT BRANCHING 61 Notice the character that prefixes the master branch it indicates the branch that you currently have checked out This means that if you commit at this point the master branch will be moved forward with your new work To see the last commit on each branch you can run git branch v git branch v iss53 93b412c fix javascript issue master 7a98805 Merge branch iss53 testing 782fd34 add scott to the author list in the readmes Another useful option to figure out what state your branches are in is to filter this list to branches that you have or have not yet merged into the branch you re currently on The useful merged and no merged options have been available in Git since version 1 5 6 for this pur pose To see which branches are already merged into the branch you re on you can run git branch merged git branch merged iss53 master Because you already merged in iss53 earlier you see it in your list Branches on this list without the in front of them are generally fine to delete with git branch d you ve already incorporated their work into
90. ve made at least the newer versions of Git 1 6 1 and later do this if you have an older version I highly recommend upgrading it to get some of these nicer usability features Let s do what it says git checkout benchmarks rb git status On branch master Changes to be committed use git reset HEAD lt file gt to unstage modified README txt Gk OH You can see that the changes have been reverted You should also realize that this is a dan gerous command any changes you made to that file are gone you just copied another file over it Don t ever use this command unless you absolutely know that you don t want the file If you just need to get it out of the way I ll go over stashing and branching in the next chapter these are generally better ways to go Remember anything that is committed in Git can almost always be recovered Even commits that were on branches that were deleted or commits that were overwritten with an amend commit can be recovered see Chapter 9 for data recovery However anything you lose that was never committed is likely never to be seen again CHAPTER 2 GIT BASICS 35 Working with Remotes To be able to collaborate on any Git project you need to know how to manage your remote repositories Remote repositories are versions of your project that are hosted on the Internet or network somewhere You can have several of them each of which generally is either read only or re
91. when the script drops you to the command line you reset that commit take the changes that have been reset and create multiple commits out of them When you save and exit the editor Git rewinds to the parent of the first commit in your list applies the first com mit f7f3f6d applies the second 3101546 and drops you to the console There you can do a mixed reset of that commit with git reset HEAD which effectively undoes that commit and leaves the modified files unstaged Now you can stage and commit files until you have several commits and run git rebase continue when you re done git reset HEAD git add README git commit m updated README formatting git add lib simplegit rb git commit m added blame git rebase continue Git applies the last commit a5f4a0d in the script and your history looks like this git log 4 pretty format h s 1c002dd added cat file 9b29157 added blame 35cfb2b updated README formatting f3cc40e changed my name a bit Once again this changes the SHAs of all the commits in your list so make sure no commit shows up in that list that you ve already pushed to a shared repository The Nuclear Option filter branch There is another history rewriting option that you can use if you need to rewrite a larger num ber of commits in some scriptable way for instance changing your e mail address globally or removing a file from every commit The command is filter branch and it can
92. you first clone a repository all of your files will be tracked and unmodified because you just checked them out and haven t edited anything As you edit files Git sees them as modified because you ve changed them since your last commit You stage these modified files and then commit all your staged changes and the cycle repeats This lifecycle is illustrated in Figure 2 1 CHAPTER 2 GIT BASICS File Status Lifecycle Unmodified Modified Fig 2 1 The lifecycle of the status of your files Checking the Status of Your Files The main tool you use to determine which files are in which state is the git status command If you run this command directly after a clone you should see something like this git status On branch master nothing to commit working directory clean This means you have a clean working directory in other words there are no tracked and modified files Git also doesn t see any untracked files or they would be listed here Finally the command tells you which branch you re on For now that is always master which is the default you won t worry about it here The next chapter will go over branches and references in detail Let s say you add a new file to your project a simple README file If the file didn t exist before and yourun git status you see your untracked file like so vim README git status On branch master Untracked files use git add lt file gt t
93. you have the Rack project under a subdirectory named rack within your project You can go into that subdirectory make changes add your own writable remote repository to push your changes into fetch and merge from the original repository and more If you run git status right after you add the submodule you see two things git status On branch master Changes to be committed use git reset HEAD lt file gt to unstage new file gitmodules new file rack He oH H 166 CHAPTER 6 GIT TOOLS First you notice the gitmodules file This is a configuration file that stores the mapping between the project s URL and the local subdirectory you ve pulled it into cat gitmodules submodule rack path rack url git github com chneukirchen rack git If you have multiple submodules you ll have multiple entries in this file It s important to note that this file is version controlled with your other files like your gitignore file It s pushed and pulled with the rest of your project This is how other people who clone this proj ect know where to get the submodule projects from The other listing in the git status output is the rack entry If you run git diff on that you see something interesting git diff cached rack diff git a rack b rack new file mode 160000 index 0000000 08d709f dev null b rack 0 0 1 QQ Subproject commit 08d709f78b8c5b0fbeb7821e37fa53e69afcf433 Although rack
94. you ll look at is the tree object which solves the problem of storing the filename and also allows you to store a group of files together Git stores content in a manner similar to a UNIX filesystem but a bit simplified All the content is stored as tree and blob objects with trees corresponding to UNIX directory entries and blobs corresponding more or less to inodes or file contents A single tree object contains one or more tree entries each of which contains an SHA 1 pointer to a blob or subtree with its associated mode type and filename For exam ple the most recent tree in the simplegit project may look something like this git cat file p master tree 100644 blob a906cb2a4a904a152e80877d4088654daad0c859 README 100644 blob 8f94139338f9404f26296befa88755fc2598c289 Rakefile 040000 tree 99f1a6d12cb4b6f19c8655fca46c3ecf317074e0 lib The master treej syntax specifies the tree object that is pointed to by the last commit on your master branch Notice that the lib subdirectory isn t a blob but a pointer to another tree git cat file p 99f1a6d12cb4b6f19c8655fca46c3ecf317074e0 100644 blob 47c6340d6459e05787f644c2447d2595f5d3a54b simplegit rb Conceptually the data that Git is storing is something like Figure 9 1 You can create your own tree Git normally creates a tree by taking the state of your stag ing area or index and writing a tree object from it So to create a tree object you first have to set up an index by staging some fil
95. 090432754092d704da8e76ca5c05c198e71a8 Mon Sep 17 00 00 00 2001 From Jessica Smith lt jessica example com gt Date Sun 6 Apr 2008 10 17 23 0700 Subject PATCH 1 2 add limit to log function Limit log functionality to the first 20 This is the beginning of the output of the format patch command that you saw in the pre vious section This is also a valid mbox e mail format If someone has e mailed you the patch properly using git send email and you download that into an mbox format then you can pointgit amto that mbox file and it will start applying all the patches it sees If you run a mail client that can save several e mails out in mbox format you can save entire patch series into a file and then usegit amto apply them one at a time However if someone uploaded a patch file generated via format patch to a ticketing sys tem or something similar you can save the file locally and then pass that file saved on your disk to git amto apply it git am 0001 limit log function patch Applying add limit to log function You can see that it applied cleanly and automatically created the new commit for you The author information is taken from the e mail s From and Date headers and the message of the commit is taken from the Subject and body before the patch of the e mail For example if this patch was applied from the mbox example I just showed the commit generated would look something like this git log pretty fuller 1 commit 6c
96. 1 1 files changed 1 insertions 0 deletions The merge goes smoothly John s commit history now looks like Figure 5 5 origin master Figure 5 5 John s repository after merging origin master CHAPTER 5 DISTRIBUTED GIT Now John can test his code to make sure it still works properly and then he can push his new merged work up to the server git push origin master To john githost simplegit git fbff5bc 72bbc59 master gt master Finally John s commit history looks like Figure 5 6 Figure 5 6 John s history after pushing to the origin server In the meantime Jessica has been working on a topic branch She s created a topic branch called issue54 and done three commits on that branch She hasn t fetched John s changes yet so her commit history looks like Figure 5 7 a uii id origin master Figure 5 7 Jessica s initial commit history Jessica wants to sync up with John so she fetches Jessica s Machine git fetch origin From jessica githost simplegit fbff5bc 72bbc59 master gt origin master 115 116 CHAPTER 5 DISTRIBUTED GIT That pulls down the work John has pushed up in the meantime Jessica s history now looks like Figure 5 8 C 4b078 ledee 738ee origin master Figure 5 8 Jessica s history after fetching John s changes Jessica thinks her topic branch is ready but she wants to know what she has to me
97. 1b0e614 040000 tree d8329fc1cc938780ffdd9f94e0d364e0ea74f579 bak 100644 blob fa49b077972391ad58037050f2a75f74e3671e92 new txt 100644 blob 1f7a7a472abf3dd9643fd615f6da379c4acb3e3a test txt If you created a working directory from the new tree you just wrote you would get the two files in the top level of the working directory and a subdirectory named bak that contained the first version of the test txt file You can think of the data that Git contains for these structures as being like Figure 9 2 3c4e9c tree new txt test txt bak Y fa49b0 1f7a7a d8329f new file version 2 tree test txt 83baae version 1 Figure 9 2 The content structure of your current Git data Commit Objects You have three trees that specify the different snapshots of your project that you want to track but the earlier problem remains you must remember all three SHA 1 values in order to recall the snapshots You also don t have any information about who saved the snapshots when they were saved or why they were saved This is the basic information that the commit object stores for you To create a commit object you call comnit tree and specify a single tree SHA 1 and which commit objects if any directly preceded it Start with the first tree you wrote echo first commit git commit tree d8329f fdf4fc3344e67ab068f836878b6c4951e3b15f3d CHAPTER 9 GIT INTERNALS 229 Now you can look at your new commit object with cat file git
98. 32 CHAPTER 2 GIT BASICS gt of bytes to be read from Jos Backus lt jos catnook com gt test for curremt head Josh Goebel lt dreamer3 gmat_c dammit this is the second time this has reverted Scott Chacon schaconfgmail c modified index to create refs heads if it is not there Scott Chacon lt schacon gmail c Add di f ics dependency Hans Engel engel amp engel uk to Add dependency for Opens Hans Engel cengel amp enogel uk to 6 merged recent changes Scott Chacon lt schacon genail c updated the Manifest file Scott Chacon schaconffgmail c fixed alternates to accept relative paths and changed i Scott Chacon schaconfgmail c added shal def to commit object Scott Chacon schaconthgmail c merged in bryces changes and fixed some testing is Scott Chacon lt schacon gmail c Clarity how to get a full count out of Repof amp comm Bryce Kerley brycefhwortdmed mime Verbes shem mm Be me otcsun7zseorcesTesabenesaroiessservtend gt amf 1 1 Wy branch idx2 Scott Chacon lt schacon genail c mem ate Mi meme Aen bie hr bent mers come Committer Scott Chacon lt schocon geail com 2009 01 30 14 23 08 Perent t 334dot13DIc7eebe328c2460betof Manes test for current heod Branch soster Follows v1 7 0 Precedes Moke the number of bytes to be read from git s stut configurable Signed off by Scott hacen schaconegesi com Se 72 11 22 19 sodule Grit include Githu
99. 499533 tree 106 107 749 fa49b077972391ad58037050f2a75f74e3671e92 blob 9 18 856 fdf4fc3344e67ab0681836878b6c4951e3b15f3d commit 177 122 627 chain length 1 1 object pack 7a16e4488ae40c7d2bc56ea2bd43e25212a66c45 pack ok Here the 9bc1d blob which if you remember was the first version of your repo rb file is referencing the 05408 blob which was the second version of the file The third column in the output is the size of the object in the pack so you can see that 05408 takes up 12K of the file but that 9bc1d only takes up 7 bytes What is also interesting is that the second version of the file is the one that is stored intact whereas the original version is stored as a delta this is because you re most likely to need faster access to the most recent version of the file The really nice thing about this is that it can be repacked at any time Git will occasionally repack your database automatically always trying to save more space You can also manually repack at any time by running git gc by hand The Refspec Throughout this book you ve used simple mappings from remote branches to local refer ences but they can be more complex Suppose you add a remote like this git remote add origin git github com schacon simplegit progit git It adds a section to your git config file specifying the name of the remote origin the URL of the remote repository and the refspec for fetching remote origin url git github com schacon simp
100. 5e70b984a60b3cecd395edd5b48a7575bf58e0 132 CHAPTER 5 DISTRIBUTED GIT Author Jessica Smith lt jessica example com gt AuthorDate Sun Apr 6 10 17 23 2008 0700 Commit Scott Chacon lt schacon gmail com gt CommitDate Thu Apr 9 09 19 06 2009 0700 add limit to log function Limit log functionality to the first 20 The Commit information indicates the person who applied the patch and the time it was applied The Author information is the individual who originally created the patch and when it was originally created But it s possible that the patch won t apply cleanly Perhaps your main branch has diverged too far from the branch the patch was built from or the patch depends on another patch you haven t applied yet In that case the git am process will fail and ask you what you want to do git am 0001 seeing if this helps the gem patch Applying seeing if this helps the gem error patch failed ticgit gemspec 1 error ticgit gemspec patch does not apply Patch failed at 0001 When you have resolved this problem run git am resolved If you would prefer to skip this patch instead run git am skip To restore the original branch and stop patching run git am abort This command puts conflict markers in any files it has issues with much like a conflicted merge or rebase operation You solve this issue much the same way edit the file to resolve the conflict stage the new file and then run git am resolved t
101. 6 the mv command isn t necessary Git started naming the hooks examples with the sample postfix only recently What does this post update hook do It looks basically like this cat git hooks post update bin sh exec git update server info This means that when you push to the server via SSH Git runs this command to update the files needed for HTTP fetching Next you need to add a VirtualHost entry to your Apache configuration with the docu ment root as the root directory of your Git projects Here I m assuming that you have wildcard DNS set up to send gitserver to whatever box you re using to run all this VirtualHost 80 ServerName git gitserver DocumentRoot opt git Directory opt git Order allow deny allow from all Directory lt VirtualHost gt You also need to set the Unix user group of the opt git directories to www data so your web server can read access the repositories because the Apache instance running the CGI script will by default be running as that user chgrp R www data opt git When you restart Apache you should be able to clone your repositories under that direc tory by specifying the URL for your project git clone http git gitserver project git This way you can set up HTTP based read access to any of your projects for a fair number of users in a few minutes Another simple option for public unauthenticated access is to start a Git daemon although that requires you
102. 65585 100644 a benchmarks rb b benchmarks rb 36 6 436 10 def main Qcommit parents 0 parents 0 parents O0 end run code x commits 1 do git commits size end run_code x commits 2 do log git commits master 15 log size That command compares what is in your working directory with what is in your staging area The result tells you the changes you ve made that you haven t yet staged If you want to see what you ve staged that will go into your next commit you can use git diff cached In Git versions 1 6 1 and later you can also use git diff staged which may be easier to remember This command compares your staged changes to your last commit git diff cached diff git a README b README new file mode 100644 index 0000000 03902a1 dev null b README2 0 0 1 5 grit by Tom Preston Werner Chris Wanstrath 22 CHAPTER 2 GIT BASICS http github com mojombo grit Grit is a Ruby library for extracting information from a Git repository It s important to note that git diff by itself doesn t show all changes made since your last commit only changes that are still unstaged This can be confusing because if you ve staged all of your changes git diff gives you no output For another example if you stage the benchmarks rb file and then edit it you can use git diff to see the changes in the file that are staged and the changes that are unstaged
103. 69 transfer protocols 16 240 244 downloading data 243 244 HTTP 240 242 smart 242 244 uploading data 242 tree filter option 161 249 tree objects 226 228 triple dot syntax 135 149 two phase merge cycle 136 U unstaging files 150 152 until option 30 untracked files 16 18 update ref command 232 233 246 update script 193 update server info command 240 upload pack process 243 244 Upstart script 95 user based ACL system enforcing 195 197 user interface 223 user name setting 11 user signingkey setting 177 user variable 201 INDEX 265 V verify pack command 237 248 version control 1 Version Control Systems VCS 1 4 W web based visualizer 90 91 WebDAV servers 83 webrick server 90 web server static 88 whitespace 181 182 whitespace errors 111 Windows installing Git on 11 workflows centralized 107 108 cherry picking 139 140 dictator and lieutenants 109 distributed 107 109 inlarge public projects 127 129 in projects 110 in small public projects 124 126 integration manager 108 large merging 137 139 merging 135 137 multiple repository 109 private managed team 118 123 private small team 112 118 rebasing 139 140 working copy 16 working directory 8 55 work themes 125 write tree command 227 X xinetd script 96 Y Your Clone URL 101 Z zlib library 231 You Need the Companion eBook Your purchase of this book entitles you to buy the
104. 6da379c4acb3e3a test txt v2 git objects 3c 4e9cd78948848d89c1073707c3585e41b0e614 it tree 3 git objects 83 baae61804e65cc73a7201a7252750c76066a30 test txt v1 git objects 95 85191f37f7b0fb9444f35a9bf50dei91beadc2 it tag git objects ca c0cab538b970a37ea1e769cbbde608743bc96d commit 2 git objects d6 70460b4b4aece5915cafs5c68d12f560a9fe3e4 test content git objects d8 329fc1cc938780ffdd9f94e0d364e0ea74f579 tree 1 git objects fa 49b077972391a4d58037050f2a75f74e3671e92 new txt git objects fd f4fc3344e67ab0681836878b6c4951e3bi5f3d commit 1 236 CHAPTER 9 GIT INTERNALS Git compresses the contents of these files with zlib and you re not storing much so all these files collectively take up only 925 bytes You ll add some larger content to the reposi tory to demonstrate an interesting feature of Git Add the repo rb file from the Grit library you worked with earlier this is about a 12K source code file curl http github com mojombo grit raw master lib grit repo rb repo rb git add repo rb git commit m added repo rb master 4842592 added repo rb 3 files changed 459 insertions 2 deletions delete mode 100644 bak test txt create mode 100644 repo rb rewrite test txt 100 If you look at the resulting tree you can see the SHA 1 value your repo rb file got for the blob object git cat file p master tree 100644 blob fa49b077972391ad58037050f2a75f74e3671e92 new txt 100644 blob 9bc1dc421dcd51
105. 78 added the index file stash 1 WIP on master c264051 Revert added file size stash 2 WIP on master 21d80a5 added number to log git stash drop stash o Dropped stash 0 364e91f3f268f0900bc3ee613f9f733e82aaed43 You can also run git stash pop to apply the stash and then immediately drop it from your stack 156 CHAPTER 6 GIT TOOLS Creating a Branch from a Stash If you stash some work leave it there for a while and continue on the branch from which you stashed the work you may have a problem reapplying the work If the apply tries to modify a file that you ve since modified you ll get a merge conflict and will have to try to resolve it If you want an easier way to test the stashed changes again you can run git stash branch which creates a new branch for you checks out the commit you were on when you stashed your work reapplies your work there and then drops the stash if it applies successfully git stash branch testchanges Switched to a new branch testchanges On branch testchanges Changes to be committed use git reset HEAD lt file gt to unstage modified index html Changed but not updated use git add file to update what will be committed modified lib simplegit rb He He it it HEHEHE HE Dropped refs stash o fodfc4d5dc332d1cee34a634182e168c4efc3359 This is a nice shortcut to recover stashed work easily and work on it in a new branch Rewriting History
106. 847eda65bf4363371d Author Richard Geiger rmg perforce com Date Tue Apr 22 20 51 34 2003 0800 Update derived jamgram c git p4 depot paths public jam src change 3108 You can see the git p4 identifier in each commit It s fine to keep that identifier there in case you need to reference the Perforce change number later However if you d like to remove the identifier now is the time to do so before you start doing work on the new repository You can use git filter branch to remove the identifier strings en masse git filter branch msg filter sed e git p4 d Rewrite 1fd4ec126171790efd2db83548b85bibbbco7dc2 123 123 Ref refs heads master was rewritten If you run git log you can see that all the SHA 1 checksums for the commits have changed but the git p4 strings are no longer in the commit messages git log 2 commit 10a16d60cffca14d454a15c6164378f4082bc5b0 Author Perforce staff supportGperforce com Date Thu Aug 19 10 18 45 2004 0800 Drop rc3 moniker of jam 2 5 Folded rc2 and rc3 RELNOTES into the main part of the document Built new tar zip balls 216 CHAPTER 8 GIT AND OTHER SYSTEMS Only 16 months later commit 2b6c6db311dd76c34c66ec1c40a49405e6b527b2 Author Richard Geiger rmg perforce com Date Tue Apr 22 20 51 34 2003 0800 Update derived jamgram c Your import is ready to push up to your new Git server A Custom Importer If your system isn t Subversion or Per
107. 87f88fce1c24ad7cOf0471 refs heads master 3ee1ecc26318164f355a883f5d99cff0c852d3c4 refs remotes my calc branch 03d09b0e2aad427e34a6d50ff147128e76c0eO0f5 refs remotes tags 2 0 2 50d02cc0adc9da4319eeba0900430ba219b9c376 refs remotes tags release 2 0 1 4caaa711a50c77879a91b8b90380060f672745cb refs remotes tags release 2 0 2 1c4cb508144c513ff1214c3488abe66dcb92916f refs remotes tags release 2 0 2rc1 1cbd490449982f3864087f88fce1c24ad7c0f0471 refs remotes trunk A normal Git repository looks more like this git show ref 83e38c7a0af325a9722f2fdc56b10188806d83a1 refs heads master 3e15e38c198baac84223acfc6224bb8b99ff2281 refs remotes gitserver master 0a30dd3b0c795b80212ae723640d4e5d48cabdff refs remotes origin master 25812380387fdd55f916652be4881c6f11600d6f refs remotes origin testing You have two remote servers one named gitserver with a master branch and another named origin with two branches master and testing Notice how in the example of remote references imported from git svn tags are added as remote branches not as real Git tags Your Subversion import looks like it has a remote named tags with branches under it Committing Back to Subversion Now that you have a working repository you can do some work on the project and push your commits back upstream using Git effectively as a SVN client If you edit one of the files and commit it you have a commit that exists in Git locally that doesn t exist on the Subversion server git commit
108. 9 refs heads master report status delete refs 003e085bb3bcb608e1e84b2432f8ecbe6306e7e7 refs heads topic 0000 CHAPTER 9 GIT INTERNALS 243 The git receive pack command immediately responds with one line for each reference it currently has in this case just the master branch and its SHA The first line also has a list of the server s capabilities here report status and delete refs Each line starts with a 4 byte hex value specifying how long the rest of the line is Your first line starts with 005b which is 91 in hex meaning that 91 bytes remain on that line The next line starts with 003e which is 62 so you read the remaining 62 bytes The next line is 0000 meaning the server is done with its references listing Now that it knows the server s state your send pack process determines what commits it has that the server doesn t For each reference that this push will update the send pack process tells the receive pack process that information For instance if you re updating the master branch and adding an experiment branch the send pack response may look something like this 0085ca8226dff817ec66144342007202690293763949 15027957951b64cf874c355730f3547bd83b3ff6 refs heads master report status 00670000000000000000000000000000000000000000 cdfdb42577e2506715f8cfeacdbabcO92bf63e8d refs heads experiment 0000 The SHA 1 value of all 0s means that nothing was there before because you re adding the experiment reference If you were d
109. 98a07c7723e65 beginning write support 0d52aaab4479697da7686c15f77a3d64d9165190 one more thing 6d52a271eda8725415634dd79daabbc4d9b6008e Merge branch experiment 0b7434486859cc7b8c3d5eidddfed66ff742fcbc added a commit function 4682c3261057305bdd616e23b64b08574832627b added a todo file 166ae0c4d3f420721acbb115cc33848dfcc2121a started write support 9fceb02d0ae598e95dc970b74767f19372d61af8 updated rakefile 964f16d36dfccde844893cac5b347e7b3d44abbc commit the todo 8a5cbc430f1a9c3d00faaeffd07798508422908a updated readme Now suppose you forgot to tag the project at v1 2 which was at the updated rakefile com mit You can add it after the fact To tag that commit you specify the commit checksum or part of it at the end of the command git tag a v1 2 9fcebo2 You can see that you ve tagged the commit git tag v0 1 v1 2 v1 3 v1 4 v1 4 lw v1 5 git show v1 2 tag v1 2 Tagger Scott Chacon lt schacon gee mail com gt Date Mon Feb 9 15 32 16 2009 0800 version 1 2 commit 9fceb02d0ae598e95dc970b74767F19372d61af8 Author Magnus Chacon lt mchacon gee mail com gt Date Sun Apr 27 20 43 35 2008 0700 updated rakefile CHAPTER 2 GIT BASICS 43 Sharing Tags By default the git push command doesn t transfer tags to remote servers You have to explic itly push tags to a shared server after you create them This process is just like sharing remote branches you can run git push origin tagname git push origin v1 5 Coun
110. After you gain a solid understanding from this book I hope you will find yourself being more productive and using Git more effectively And more important I hope you will enjoy using Git Junio C Hamano Git Project Leader XV About the Author SCOTT CHACON is a Git evangelist and Ruby developer employed at Logical Awesome working on GitHub com the largest Git hosting web site He is the author of the Git Internals Peepcode PDF in addition to maintaining the Git home page git scm com and the Git Community Book book git scm com Scott has presented at conferences such as RailsConf RubyConf RubyKaigi Scotland on Rails and OSCon as well as for companies such as Google Yahoo and Digg Scott occasionally talks about Git for a number of local groups and has done corporate training on Git across the country xvii xviii About the Technical Reviewer SHAWN PEARCE is the second in command of the Git project He has been actively involved in the project since early 2006 contributing more than 1 300 changes in three years Shawn is the author of git gui a Tk based graphical interface shipped with Git and git fast import a stream based import system often used for converting projects to Git In addition Shawn s opinion backed by his code has influenced many key design decisions that form the modern Git implementation In early 2006 Shawn founded the JGit project creating a 100 pure Java reimplemen tation of the Git vers
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112. Bv2 The squash option takes all the work on the merged branch and squashes it into one non merge commit on top of the branch you re on The no commit option tells Git not to automatically record a commit This allows you to introduce all the changes from another branch and then make more changes before recording the new commit CHAPTER 5 DISTRIBUTED GIT Now you can send the maintainer a message that you ve made the requested changes and they can find those changes in your featureBv2 branch see Figure 5 18 master origin master T j biis 17f4d featureBv2 Figure 5 18 Commit history after featureBv2 work featureA i Public Large Project Many larger projects have established procedures for accepting patches you ll need to check the specific rules for each project because they will differ However many larger public proj ects accept patches via a developer mailing list so I ll go over an example of that now The workflow is similar to the previous use case you create topic branches for each patch series you work on The difference is how you submit them to the project Instead of forking the project and pushing to your own writable repository you generate e mail versions of each commit series and e mail them to the developer mailing list git checkout b topicA work git commit work git commit Now you have two commits that you want to send to the mailing list You use git form
113. CHING 51 vim test rb git commit a m made a change Figure 3 7 illustrates the result if HH Figure 3 7 The branch that HEAD points to moves forward with each commit This is interesting because now your testing branch has moved forward but your master branch still points to the commit you were on when you ran git checkout to switch branches Let s switch back to the master branch git checkout master Figure 3 8 shows the result pa i Hi Figure 3 8 HEAD moves to another branch on a checkout 52 CHAPTER 3 GIT BRANCHING That command did two things It moved the HEAD pointer back to point to the master branch and it reverted the files in your working directory back to the snapshot that master points to This also means the changes you make from this point forward will diverge from an older version of the project It essentially rewinds the work you ve done in your testing branch temporarily so you can go in a different direction Let s make a few changes and commit again vim test rb git commit a m made other changes Now your project history has diverged see Figure 3 9 You created and switched to a branch did some work on it and then switched back to your main branch and did other work Both of those changes are isolated in separate branches you can switch back and forth between the branches and merge them together when you re ready And you did all that with s
114. Copy this file to your home directory and add this to your bashrc file source git completion bash 44 CHAPTER 2 GIT BASICS If you want to set up Git to automatically have Bash shell completion for all users copy this script to the opt local etc bash_completion d directory on Mac systems or to the etc bash_completion d directory on Linux systems This is a directory of scripts that Bash will automatically load to provide shell completions If you re using Windows with Git Bash which is the default when installing Git on Windows with msysGit auto completion should be preconfigured Press the Tab key when you re writing a Git command and it should return a set of suggestions for you to pick from git co lt tab gt lt tab gt commit config In this case typing git co and then pressing the Tab key twice suggests commit and config Adding m lt tab gt completes git commit automatically This also works with options which is probably more useful For instance if you re run ningagit log command and can t remember one of the options you can start typing it and press Tab to see what matches git log s lt tab gt shortstat since src prefix stat summary That s a pretty nice trick and may save you some time and documentation reading Git Aliases Git doesn t infer your command if you type it in partially If you don t want to type the entire text of each of the Git commands you can easily set up an alias
115. D GIT Let s say the project maintainer has pulled in a bunch of other patches and tried your first branch but it no longer cleanly merges In this case you can try to rebase that branch on top of origin master resolve the conflicts for the maintainer and then resubmit your changes git checkout featureA git rebase origin master git push f myfork featureA This rewrites your history to now look like Figure 5 17 origin master i 5 co estos Jaf e Figure 5 17 Commit history after featureA work Because you rebased the branch you have to specify the f to your push command in order to be able to replace the featureA branch on the server with a commit that isn t a descendant of it An alternative would be to push this new work to a different branch on the server perhaps called featureAv2 Let s look at one more possible scenario the maintainer has looked at work in your second branch and likes the concept but would like you to change an implementation detail You ll also take this opportunity to move the work to be based off the project s current master branch You start a new branch based off the current origin master branch squash the featureB changes there resolve any conflicts make the implementation change and then push that up as a new branch git checkout b featureBv2 origin master git merge no commit squash featureB change implementation git commit git push myfork feature
116. Doing so launches your editor of choice This is set by your shell s EDITOR environment variable usually vim or emacs although you can configure it with whatever you want using the git config global core editor command as you saw in Chapter 1 The editor displays the following text this example is a Vim screen Please enter the commit message for your changes Lines starting with will be ignored and an empty message aborts the commit On branch master Changes to be committed use git reset HEAD lt file gt to unstage new file README modified benchmarks rb 2 xt tt H 2 git COMMIT EDITMSG 10L 283C You can see that the default commit message contains the latest output of the git status command commented out and one empty line on top You can remove these comments and type your commit message or you can leave them there to help you remember what you re committing For an even more explicit reminder of what you ve modified you can pass the voption to git commit Doing so also puts the diff of your change in the editor so you can see exactly what you did When you exit the editor Git creates your commit with that commit message with the comments and diff stripped out Alternatively you can type your commit message inline with the comnit command by specifying it after a m flag like this git commit m Story 182 Fix benchmarks for speed master created 463dc4f Fix benchmarks for spe
117. ERNALS Oops you didn t want to add a huge tarball to your project Better get rid of it git rm git tbz2 rm git tbz2 git commit m oops removed large tarball master da3f30d oops removed large tarball 1 files changed 0 insertions 0 deletions delete mode 100644 git tbz2 Now gc your database and see how much space you re using git gc Counting objects 21 done Delta compression using 2 threads Compressing objects 100 16 16 done Writing objects 100 21 21 done Total 21 delta 3 reused 15 delta 1 You can run the count objects command to quickly see how much space you re using git count objects v count 4 size 16 in pack 21 packs 1 size pack 2016 prune packable O garbage O The size pack entry is the size of your packfiles in kilobytes so you re using 2MB Before the last commit you were using closer to 2K clearly removing the file from the previous commit didn t remove it from your history Every time anyone clones this repository they will have to clone all 2MB just to get this tiny project because you accidentally added a big file Let s get rid of it First you have to find it In this case you already know what file it is But suppose you didn t how would you identify what file or files were taking up so much space If you run git gc all the objects are in a packfile you can identify the big objects by running another plumb ing command called git verify pac
118. If you re interested in using the HTTP push protocols you can read about preparing a repository for this purpose at http www kernel org pub software scm git docs howto setup git server over http txt One nice thing about making Git push over HTTP is that you can use any WebDAV server without specific Git features so you can use this functionality if your web hosting provider supports WebDAV for writing updates to your web site The Pros The upside of using the HTTP protocol is that it s easy to set up Running the handful of required commands gives you a simple way to give the world read access to your Git reposi tory It takes only a few minutes to do The HTTP protocol also isn t very resource intensive on your server Because it generally uses a static HTTP server to serve all the data a normal Apache server can serve thousands of files per second on average it s difficult to overload even a small server You can also serve your repositories read only over HTTPS which means you can encrypt the content transfer or you can go so far as to make the clients use specific signed SSL certifi cates Generally if you re going to these lengths it s easier to use SSH public keys but it may be a better solution in your specific case to use signed SSL certificates or other HTTP based authentication methods for read only access over HTTPS Another nice thing is that HTTP is such a commonly used protocol that corporate firewalls are often set
119. In Chapter 7 you ll learn how to do more complicated manual project imports 102 CHAPTER 4 GIT ON THE SERVER Adding Collaborators You ll now add the rest of the team If John Josie and Jessica all sign up for accounts on GitHub and you want to give them push access to your repository you can add them to your project as collaborators Doing so allows pushes from their public keys to work Click the edit button in the project header or the Admin tab at the top of the project to reach the Admin page of your GitHub project see Figure 4 10 gt testinguser iphone_project iphone project for our mobile group edit Click to edit edit git github com testinguser iphone project git jE git github com t estinguser iphone project git ij Generate Your Project Page Add auto responder y o Donations 7 Inactive edit Privacy Repository Collaborators gt This repo is viewable by everyone Add another collaborator If you uparade your plan you can make this repository private Figure 4 10 GitHub administration page To give another user write access to your project click the Add another collaborator link A new text box appears into which you can type a username As you type a helper pops up showing you possible username matches When you find the correct user click the Add button to add that user as a collaborator on your project see Figure 4 11 Repository Collaborators chaser aa
120. R enable push access but given the lack of authentication if you turn on push access anyone on the Internet who finds your project s URL could push to your project Suffice it to say that this is rare The Pros The Git protocol is the fastest transfer protocol available If you re serving a lot of traffic for a public project or serving a very large project that doesn t require user authentication for read access it s likely that you ll want to set up a Git daemon to serve your project It uses the same data transfer mechanism as the SSH protocol but without the encryption and authentication overhead The Cons The downside of the Git protocol is the lack of authentication It s generally undesirable for the Git protocol to be the only access to your project Generally you ll pair it with SSH access for the few developers who have push write access and have everyone else use git for read only access It s also probably the most difficult protocol to set up It must run its own daemon which is custom you ll look at setting one up in the Gitosis section of this chapter and it requires xinetd configuration or the like which isn t always a walk in the park It also requires firewall access to port 9418 which isn t a standard port that corporate firewalls always allow Behind big corporate firewalls this obscure port is commonly blocked The HTTP S Protocol Last you have the HTTP protocol The beauty of the HTTP or H
121. TED GIT 125 are available in the git repository at git githost simplegit git featureA Jessica Smith 2 add limit to log function change log output to 30 from 25 lib simplegit rb 10 1 files changed 9 insertions 1 deletions The output can be sent to the maintainer it tells them where the work was branched from summarizes the commits and tells where to pull this work from On a project for which you re not the maintainer it s generally easier to have a branch like master always track origin master and to do your work in topic branches that you can easily dis card if they re rejected Having work themes isolated into topic branches also makes it easier for you to rebase your work if the tip of the main repository has moved in the meantime and your commits no longer apply cleanly For example if you want to submit a second topic of work to the project don t continue working on the topic branch you just pushed up start over from the main repository s master branch git checkout b featureB origin master work git commit git push myfork featureB email maintainer git fetch origin Now each of your topics is contained within a silo similar to a patch queue that you can rewrite rebase and modify without the topics interfering or interdepending on each other as in Figure 5 16 me rur Figure 5 16 Initial commit history with featureB work 126 CHAPTER 5 DISTRIBUTE
122. TER 6 GIT TOOLS 163 where snippets of code within it originally came from if they were copied from elsewhere Recently I was refactoring a file named GITServerHandler m into multiple files one of which was GITPackUpload m By blaming GITPackUpload m with the C option I could see where sec tions of the code originally came from git blame C L 141 153 GITPackUpload m f344f58d GITServerHandler m Scott 2009 01 04 141 f344f58d GITServerHandler m Scott 2009 01 04 142 void gatherObjectShasFromC f344f58d GITServerHandler m Scott 2009 01 04 143 70befddd GITServerHandler m Scott 2009 03 22 144 NSLog G GATHER COMMI ad11ac80 GITPackUpload m Scott 2009 03 24 145 adi1ac80 GITPackUpload m Scott 2009 03 24 146 NSString parentSha ad11ac80 GITPackUpload m Scott 2009 03 24 147 GITCommit commit g ad11ac80 GITPackUpload m Scott 2009 03 24 148 ad11ac80 GITPackUpload m Scott 2009 03 24 149 NSLog GATHER COMMI ad11ac80 GITPackUpload m Scott 2009 03 24 150 56ef2caf GITServerHandler m Scott 2009 01 05 151 if commit 56ef2caf GITServerHandler m Scott 2009 01 05 152 refDict setOb 56ef2caf GITServerHandler m Scott 2009 01 05 153 This is really useful Normally you get as the original commit the commit where you cop ied the code over because that is the first time you touched those lines in this file Git tells you the original commit where you wrote those lines even if it was in another file Binary Se
123. THE EXPERT S VOICE IN SOFTWARE DEVELOPMENT Everything you need to know about the Git distributed source control tool ai Pro Git Scott Chacon Apress Pro Git Copyright 2009 by Scott Chacon Permission is granted to copy distribute and or modify this document under the terms of the Creative Commons Attribution NonCommercial ShareAlike 3 0 Unported License Apress http www apress com and the author s ask for your support by buying the print or eBook edition through any online or retail outlet A copy of the license is included in the section entitled Creative Commons Legal Code All rights reserved subject to the Creative Commons license ISBN 13 pbk 978 1 4302 1833 3 ISBN 13 electronic 978 1 4302 1834 0 Printed and bound in the United States of America9 87654321 The Git logo on this book s cover comes from http en wikipedia org wiki File Git logo svg where itis available under the GNU General Public License It is available from http apress com book view 1430218339 You may redistribute it and or modify it under the terms of the GPL http www gnu org copyleft gpl html as published by the Free Software Foundation either version 2 of the License or any later version Trademarked names may appear in this book Rather than use a trademark symbol with every occurrence of a trademarked name we use the names only in an editorial fashion and to the benefit of the trademark owner with no intenti
124. THE SERVER 81 It s also important to mention that this isn t necessarily the fastest option if you re using a shared mount of some kind A local repository is fast only if you have fast access to the data A repository on NFS is often slower than the repository over SSH on the same server allowing Git to run off local disks on each system The SSH Protocol Probably the most common transport protocol for Git is SSH This is because SSH access to servers is already set up in most places and if it isn t it s easy to do SSH is also the only network based protocol that you can easily read from and write to The other two network protocols HTTP and Git are generally read only so even if you have them available for the unwashed masses you still need SSH for your own write commands SSH is also an authenti cated network protocol and because it s ubiquitous it s generally easy to set up and use To clone a Git repository over SSH you can specify ssh URL like this git clone ssh user server project git Or you can not specify a protocol Git assumes SSH if you aren t explicit git clone user server project git You can also not specify a user and Git assumes the user you re currently logged in as The Pros The pros of using SSH are many First you basically have to use it if you want authenticated write access to your repository over a network Second SSH is relatively easy to set up SSH daemons are commonplace many network
125. TTPS protocol is the simplic ity of setting it up Basically all you have to do is put the bare Git repository under your HTTP document root and set up a specific post receive hook and you re done See Chapter 7 for details on Git hooks At that point anyone who can access the web server under which you put the repository can also clone your repository To allow read access to your repository over HTTP do something like this cd var www htdocs git clone bare path to git project gitproject git cd gitproject git mv hooks post update sample hooks post update chmod a x hooks post update That s all The post update hook that comes with Git by default runs the appropriate command git update server info to make HTTP fetching and cloning work properly This command is run when you push to this repository over SSH then other people can clone via something like git clone http example com gitproject git In this particular case you re using the var www htdocs path that is common for Apache setups but you can use any static web server just put the bare repository in its path The Git data is served as basic static files see Chapter 9 for details about exactly how it s served CHAPTER 4 GIT ON THE SERVER 83 It s possible to make Git push over HTTP as well although that technique isn t as widely used and requires you to set up complex WebDAV requirements Because it s rarely used I won t cover it in this book
126. Tagging Your Releases When you ve decided to cut a release you ll probably want to drop a tag so you can re create that release at any point going forward You can create a new tag as I discussed in Chapter 2 If you decide to sign the tag as the maintainer the tagging may look something like this git tag s v1 5 m my signed 1 5 tag You need a passphrase to unlock the secret key for user Scott Chacon lt schacon gmail com gt 1024 bit DSA key ID F721C45A created 2009 02 09 If you do sign your tags you may have the problem of distributing the public PGP key used to sign your tags The maintainer of the Git project has solved this issue by including their public key as a blob in the repository and then adding a tag that points directly to that content To do this you can figure out which key you want by running gpg list keys gpg list keys Users schacon gnupg pubring gpg pub 1024D F721C45A 2009 02 09 expires 2010 02 09 uid Scott Chacon schaconggmail com sub 2048g 45D02282 2009 02 09 expires 2010 02 09 Then you can directly import the key into the Git database by exporting it and piping that through git hash object which writes a new blob with those contents into Git and gives you back the SHA 1 of the blob gpg a export F721C45A git hash object w stdin 659ef797d181633c87ec71ac3f9ba29fe5775b92 Now that you have the contents of your key in Git you can create a tag that points directly to it b
127. a or done lt ram gd Figure 4 11 Adding a collaborator to your project When you re finished adding collaborators you should see a list of them in the Repository Collaborators box see Figure 4 12 If you need to revoke access to individuals you can click the revoke link and their push access will be removed For future projects you can also copy collaborator groups by copying the permissions of an existing project CHAPTER 4 GIT ON THE SERVER Repository Collaborators il schacon revoke duncanparkes revoke spearce revoke Figure 4 12 A list of collaborators on your project Your Project After you push your project up or have it imported from Subversion you have a main project page that looks something like Figure 4 13 github el e rumen em m im Source Commits Network 1 Downloads 0 Wiki 1 Graphs master ail branches all tags testinguser iphone project watch download GD GD 9 Description iphone project for our mobile group Clone URL git github com testinguser iphone project git li initial commit commit B8ce9cc660e706384c1241232cf15b2bdc447574a sducon BORA tree C3o8f S888d80f 608 c71fO07f 5f c5821of 11642485 5 days ago iphone project name oge message history Classes 5 days ago initial commit schacon Info plist 5 days ago initial commit schacon MainWindow xib 5 days ago initial commit schacon build 5 days ago initial commit schacon iGit xcodeproj
128. a clone of a project you must distribute these scripts some other way and then have your users copy them to their git hooks directory and make them executable You can distribute these hooks within the project or in a separate project but there is no way to set them up automatically To begin you should check your commit message just before each commit is recorded so you know the server won t reject your changes due to badly formatted commit messages To do this you can add the commit msg hook If you have it read the message from the file passed as the first argument and compare that to the pattern you can force Git to abort the commit if there is no match usr bin env ruby message file ARGV O message File read message file regex ref d if regex match message puts POLICY Your message is not formatted correctly exit 1 end If that script is in place in git hooks commit msg and executable and you commit with a message that isn t properly formatted you see this git commit am test POLICY Your message is not formatted correctly No commit was completed in that instance However if your message contains the proper pattern Git allows you to commit git commit am test ref 132 master e05c914 test ref 132 1 files changed 1 insertions 0 deletions 200 CHAPTER 7 CUSTOMIZING GIT Next you want to make sure you aren t modifying files that are outside your ACL scope I
129. a9 34ac2 f30ab tee 0dez4 parem saae commer scos author seors fixed bug 1328 stock odd feature 32 obility to overflow under certain odd new formats to the central Snapshot A Snapshot B Snapshot C Figure 3 2 Git object data for multiple commits Figure 3 3 Branch pointing into the commit data s history This creates a new pointer at the same commit you re currently on see Figure 3 4 sie fa ce j em Figure 3 4 Multiple branches pointing into the commit s data history 50 CHAPTER 3 GIT BRANCHING How does Git know what branch you re currently on It keeps a special pointer called HEAD Note that this is a lot different than the concept of HEAD in other VCSs you may be used to such as Subversion or CVS In Git this is a pointer to the local branch you re currently on In this case you re still on master The git branch command only created a new branch it didn t switch to that branch see Figure 3 5 master se fa omo Figure 3 5 HEAD file pointing to the branch you re on To switch to an existing branch you run the git checkout command Let s switch to the new testing branch git checkout testing This moves HEAD to point to the testing branch see Figure 3 6 Figure 3 6 HEAD points to another branch when you switch branches What is the significance of that Well do another commit CHAPTER 3 GIT BRAN
130. above Licensor reserves the right to release the Work under different license terms or to stop distributing the Work at any time provided however that any such elec tion will not serve to withdraw this License or any other license that has been or is required to be granted under the terms of this License and this License will con tinue in full force and effect unless terminated as stated above APPENDIX CREATIVE COMMONS LEGAL CODE 257 8 Miscellaneous a Each time You Distribute or Publicly Perform the Work or a Collection the Licensor offers to the recipient a license to the Work on the same terms and conditions as the license granted to You under this License b Each time You Distribute or Publicly Perform an Adaptation Licensor offers to the recipient a license to the original Work on the same terms and conditions as the license granted to You under this License c If any provision of this License is invalid or unenforceable under applicable law it shall not affect the validity or enforceability of the remainder of the terms of this License and without further action by the parties to this agreement such provision shall be reformed to the minimum extent necessary to make such provision valid and enforceable d No term or provision of this License shall be deemed waived and no breach con sented to unless such waiver or consent shall be in writing and signed by the party to be charged with such waiver or consent e T
131. acon geemail com gt Date Sun May 3 00 12 22 2009 0000 fixed install go to trunk Not only does the Author field look a lot better but the git svn idis no longer there either You then need to do a bit of post import cleanup For one thing you should clean up the weird references that git svn set up First you ll move the tags so they re actual tags rather than strange remote branches and then you ll move the rest of the branches so they re local To move the tags to be proper Git tags run cp Rf git refs remotes tags git refs tags rm Rf git refs remotes tags This takes the references that were remote branches that started with tag and makes them real lightweight tags Next move the rest of the references under refs remotes to be local branches cp Rf git refs remotes git refs heads rm Rf git refs remotes Now all the old branches are real Git branches and all the old tags are real Git tags The last thing to do is add your new Git server as a remote and push to it Because you want all your branches and tags to go up you can run this git push origin all All your branches and tags should be on your new Git server in a nice clean import Perforce The next system you ll look at importing from is Perforce A Perforce importer is also distrib uted with Git but only in the contrib section of the source code it isn t available by default likegit svn To run it you must get the Git source c
132. ad write for you Collaborating with others involves managing these remote repositories and pushing and pulling data to and from them when you need to share work Managing remote repositories includes knowing how to add remote repositories remove remotes that are no longer valid manage various remote branches and define them as being tracked or not and more In this section I ll cover these remote management skills Showing Your Remotes To see which remote servers you have configured you can run the git remote command It lists the shortnames of each remote handle you ve specified If you ve cloned your repository you should at least see origin that is the default name Git gives to the server you cloned from git clone git github com schacon ticgit git Initialized empty Git repository in private tmp ticgit git remote Counting objects 595 done remote Compressing objects 100 269 269 done remote Total 595 delta 255 reused 589 delta 253 Receiving objects 100 595 595 73 31 KiB 1 KiB s done Resolving deltas 100 255 255 done cd ticgit git remote origin You can also specify v which shows you the URL that Git has stored for the shortname to be expanded to git remote v origin git github com schacon ticgit git If you have more than one remote the command lists them all For example my Grit repository looks something like this cd grit git remote v bakkdoor git github com bakkd
133. ally easier to run the git config command 175 176 CHAPTER 7 CUSTOMIZING GIT Basic Client Configuration The configuration options recognized by Git fall into two categories client side and server side The majority of the options are client side configuring your personal working prefer ences Although tons of options are available I ll only cover the few that either are commonly used or can significantly affect your workflow Many options are useful only in edge cases that I won t go over here If you want to see a list of all the options your version of Git recognizes you can run git config help The manual page for git config lists all the available options in quite a bit of detail core editor By default Git uses whatever you ve set as your default text editor or else falls back to the Vi editor to create and edit your commit and tag messages To change that default to something else you can use the core editor setting git config global core editor emacs Now no matter what is set as your default shell editor variable Git will fire up Emacs to edit messages commit template If you set this to the path of a file on your system Git will use that file as the default message when you commit For instance suppose you create a template file at HOME gitmessage txt that looks like this subject line what happened ticket X To tell Git to use it as the default message that appears in your editor whe
134. am or perfor mance and includes cinematographic adaptations or any other form in which the Work may be recast transformed or adapted including in any form recognizably derived from the original except that a work that constitutes a Collection will not 251 252 APPENDIX CREATIVE COMMONS LEGAL CODE be considered an Adaptation for the purpose of this License For the avoidance of doubt where the Work is a musical work performance or phonogram the synchro nization of the Work in timed relation with a moving image synching will be considered an Adaptation for the purpose of this License Collection means a collection of literary or artistic works such as encyclopedias and anthologies or performances phonograms or broadcasts or other works or subject matter other than works listed in Section 1 g below which by reason of the selection and arrangement of their contents constitute intellectual creations in which the Work is included in its entirety in unmodified form along with one or more other contributions each constituting separate and independent works in themselves which together are assembled into a collective whole A work that con stitutes a Collection will not be considered an Adaptation as defined above for the purposes of this License Distribute means to make available to the public the original and copies of the Work or Adaptation as appropriate through sale or other transfer of owners
135. anymore This is particularly useful if you forgot to add some thing to your gitignore file and accidentally added it like a large log file or a bunch of a compiled files To do this use the cached option git rm cached readme txt You can pass files directories and file glob patterns to the git rm command That means you can do things such as git rm log log Note the backslash in front of the This is necessary because Git does its own file name expansion in addition to your shell s filename expansion This command removes all files that have the log extension in the log directory Or you can do something like this git rm This command removes all files that end with Moving Files Unlike many other VCS systems Git doesn t explicitly track file movement If you rename a file in Git no metadata is stored in Git that tells it you renamed the file However Git is pretty smart about figuring that out after the fact you ll deal with detecting file movement a bit later Thus it s a bit confusing that Git has a mv command If you want to rename a file in Git you can run something like git mv file from file to 26 CHAPTER 2 GIT BASICS and it works fine In fact if you run something like this and look at the status you ll see that Git considers it a renamed file git mv README txt README git status On branch master Your branch is ahead of origin master by 1 commit
136. ar www gitweb Directory var www gitweb Options ExecCGI FollowSymLinks SymLinksIfOwnerMatch AllowOverride All order allow deny Allow from all AddHandler cgi script cgi DirectoryIndex gitweb cgi lt Directory gt lt VirtualHost gt Again GitWeb can be served with any CGI capable web server if you prefer to use some thing else it shouldn t be difficult to set up At this point you should be able to visit http gitserver to view your repositories online and you can use http git gitserver to clone and fetch your repositories over HTTP Gitosis Keeping all users public keys in the authorized keys file for access works well only for a while When you have hundreds of users it s much more of a pain to manage that process You have to shell onto the server each time and there is no access control everyone in the file has read and write access to every project You may want to turn to a widely used software project called Gitosis Gitosis is basically a set of scripts that help you manage the authorized keys file as well as implement some sim ple access controls The really interesting part is that the UI for this tool for adding people and determining access isn t a web interface but a special Git repository You set up the informa tion in that project and when you push it Gitosis reconfigures the server based on that which is cool 92 CHAPTER 4 GIT ON THE SERVER Installing Gitosis isn t the simplest task ever
137. arch Annotating a file helps if you know where the issue is to begin with If you don t know what is breaking and there have been dozens or hundreds of commits since the last state where you know the code worked you ll likely turn to git bisect for help The bisect command does a binary search through your commit history to help you identify as quickly as possible which commit introduced an issue Let s say you just pushed out a release of your code to a production environment you re getting bug reports about something that wasn t happening in your development environ ment and you can t imagine why the code is doing that You go back to your code and it turns out you can reproduce the issue but you can t figure out what is going wrong You can bisect the code to find out First yourun git bisect start to get things going and then you use git bisect badto tell the system that the current commit you re on is broken Then you must tell bisect when the last known good state was using git bisect good good commit git bisect start git bisect bad git bisect good v1 0 Bisecting 6 revisions left to test after this ecb6e1bc347ccecc5f93504878ce677feb13d3b2 error handling on repo Git figured out that about 12 commits came between the commit you marked as the last good commit v1 0 and the current bad version and it checked out the middle one for you At this point you can run your test to see if the issue exists as of this commit If
138. arget shas each do sha remote refs each do remote ref shas pushed git rev list sha refs remotes remote_ref if shas_pushed split n include sha puts POLICY Commit sha has already been pushed to remote_ref exit 1 end end end This script uses a syntax that wasn t covered in the Revision Selection section of Chapter 6 You get a list of commits that have already been pushed up by running this git rev list sha refs remotes H remote ref The SHA 0 syntax resolves to all the parents of that commit You re looking for any commit that is reachable from the last commit on the remote and that isn t reachable from any parent of any of the SHAs you re trying to push up meaning it s a fast forward The main drawback to this approach is that it can be very slow and is often unnecessary if you don t try to force the push with f the server will warn you and not accept the push However it s an interesting exercise and can in theory help you avoid a rebase that you might later have to go back and fix 202 CHAPTER 7 CUSTOMIZING GIT Summary You ve covered most of the major ways that you can customize your Git client and server to best fit your workflow and projects You ve learned about all sorts of configuration settings file based attributes and event hooks and you ve built an example policy enforcing server You should now be able to make Git fit nearly any workflow you can dream up CHAPTER 8 G
139. arned while using BitKeeper Some of the goals of the new system were as follows Speed Simple design Strong support for non linear development thousands of parallel branches Fully distributed Ability to handle large projects like the Linux kernel efficiently speed and data size Since its birth in 2005 Git has evolved and matured to be easy to use and yet retain these initial qualities It s incredibly fast it s very efficient with large projects and it has an incred ible branching system for non linear development See Chapter 3 Git Basics So what is Git in a nutshell This is an important section to absorb because if you understand what Git is and the fundamentals of how it works then using Git effectively will probably be much easier for you As you learn Git try to clear your mind of the things you may know about other VCSs such as Subversion and Perforce doing so will help you avoid subtle confusion when using the tool Git stores and thinks about information much differently than these other systems even though the user interface is fairly similar understanding those differences will help prevent you from becoming confused while using it CHAPTER 1 GETTING STARTED Snapshots Not Differences The major difference between Git and any other VCS Subversion and friends included is the way Git thinks about its data Conceptually most other systems store information as a list of file based changes These syst
140. art using Git you must migrate your project one way or another This section goes over some importers that are included with Git for common systems and then demonstrates how to develop your own cus tom importer CHAPTER 8 GIT AND OTHER SYSTEMS 213 Importing You ll learn how to import data from two of the bigger professionally used SCM systems Subversion and Perforce both because they make up the majority of users I hear of who are currently switching and because high quality tools for both systems are distributed with Git Subversion If you read the previous section about using git svn you can easily use those instructions to git svn clone a repository then stop using the Subversion server push to a new Git server and start using that If you want the history you can accomplish that as quickly as you can pull the data out of the Subversion server which may take a while However the import isn t perfect and because it will take so long you may as well do it right The first problem is the author information In Subversion each person committing has a user on the system who is recorded in the commit information The examples in the previous section show schacon in some places such as the blame output and the git svn log If you want to map this to better Git author data you need a mapping from the Subversion users to the Git authors Create a file called users txt that has this mapping in a format like this schacon Scott
141. as initialized the objects directory and created pack and info subdirectories in it but there are no regular files Now store some text in your Git database echo test content git hash object w stdin d670460b4b4aece5915caf5c68d12f560a9fe3e4 The w tells hash object to store the object otherwise the command simply tells you what the key would be stdin tells the command to read the content from stdin if you don t spec ify this hash object expects the path to a file The output from the command is a 40 character checksum hash This is the SHA 1 hash a checksum of the content you re storing plus a header which you ll learn about in a bit Now you can see how Git has stored your data find git objects type f git objects d6 70460b4b4aece5915caf5c68d12f560a9fe3e4 You can see a file in the objects directory This is how Git stores the content initially as a single file per piece of content named with the SHA 1 checksum of the content and its header The subdirectory is named with the first 2 characters of the SHA and the filename is the remaining 38 characters You can pull the content back out of Git with the cat file command This command is sort of a Swiss army knife for inspecting Git objects Passing p to it instructs the cat file command to figure out the type of content and display it nicely for you git cat file p d670460b4b4aece5915caf5c68d12f560a9fe3e4 test content Now you can add content to Git and pu
142. ase isn t that big so it takes just a few minutes However Git has to check out each version one at a time and commit it individually For a project with hundreds or thousands of commits this can literally take hours or even days to finish The T trunk b branches t tags part tells Git that this Subversion repository follows the basic branching and tagging conventions If you name your trunk branches or tags differ ently you can change these options Because this is so common you can replace this entire part with s which means standard layout and implies all those options The following com mand is equivalent git svn clone file tmp test svn s At this point you should have a valid Git repository that has imported your branches and tags git branch a master my calc branch tags 2 0 2 tags release 2 0 1 tags release 2 0 2 tags release 2 0 2rc1 trunk It s important to note how this tool namespaces your remote references differently When you re cloning a normal Git repository you get all the branches on that remote server available locally as something like origin branch namespaced by the name of the remote However git svn assumes that you won t have multiple remotes and saves all its references to points on the remote server with no namespacing You can use the Git plumbing command show ref to look at all your full reference names 206 CHAPTER 8 GIT AND OTHER SYSTEMS git show ref 1cbd4904d9982f386d
143. aster branch used to be making the first two commits reachable again CHAPTER 9 GIT INTERNALS 247 Next suppose your loss was for some reason not in the reflog you can simulate that by removing recover branch and deleting the reflog Now the first two commits aren t reachable by anything git branch D recover branch rm Rf git logs Because the reflog data is kept in the git logs directory you effectively have no reflog How can you recover that commit at this point One way is to use thegit fsck utility which checks your database for integrity If you run it with the full option it shows you all objects that aren t pointed to by another object git fsck full dangling blob d670460b4b4aece5915caf5c68d12f560a9fe3e4 dangling commit abiafef80fac8e34258ff41fc1b867c702daa24b dangling tree aea790b9a58f6cf6f2804eeac9fOabbe9631e4c9 dangling blob 7108f7ecb345ee9d0084193f147cdad4d2998293 In this case you can see your missing commit after the dangling commit You can recover it the same way by adding a branch that points to that SHA Removing Objects There are a lot of great things about Git but one feature that can cause issues is the fact that a Git clone downloads the entire history of the project including every version of every file This is fine if the whole thing is source code because Git is highly optimized to compress that data efficiently However if someone at any point in the history of your project added
144. at John and Jessica are working together on one feature while Jessica and Josie are working on a second In this case the company is using a type of integration manager workflow where the work of the individual groups is integrated only by certain engineers and the master branch of the main repository can be updated only by those engineers In this sce nario all work is done in team based branches and pulled together by the integrators later CHAPTER 5 DISTRIBUTED GIT 119 Let s follow Jessica s workflow as she works on her two features collaborating in parallel with two different developers in this environment Assuming she already has her repository cloned she decides to work on featured first She creates a new branch for the feature and does some work on it there Jessica s Machine git checkout b featureA Switched to a new branch featureA vim lib simplegit rb git commit am add limit to log function featureA 3300904 add limit to log function 1 files changed 1 insertions 1 deletions At this point she needs to share her work with John so she pushes her featureA branch commits up to the server Jessica doesn t have push access to the master branch only the integrators do so she has to push to another branch in order to collaborate with John git push origin featureA To jessica githost simplegit git new branch featureA featureA Jessica e mails John to tell him that she s pushed some work int
145. at learning this information was fundamentally important to understanding how useful and powerful Git is but others have argued to me that it can be confusing and unnecessarily complex for beginners Thus I ve made this discussion the last chapter in the book so you could read it early or later in your learning process I leave it up to you to decide Now that you re here let s get started First if it isn t yet clear Git is fundamentally a content addressable filesystem with a VCS user interface written on top of it You ll learn more about what this means in a bit In the early days of Git mostly pre 1 5 the user interface was much more complex because it emphasized this filesystem rather than a polished VCS In the last few years the UI has been refined until it s as clean and easy to use as any system out there but often the ste reotype lingers about the early Git UI that was complex and difficult to learn The content addressable filesystem layer is amazingly cool so I ll cover that first in this chapter then you ll learn about the transport mechanisms and the repository maintenance tasks that you may eventually have to deal with Plumbing and Porcelain This book covers how to use Git with 30 or so verbs such as checkout branch remote and so on But because Git was initially a toolkit for a VCS rather than a full user friendly VCS it has a bunch of verbs that do low level work and were designed to be chained together UNIX styl
146. at object again at some point you ll always get the data of the first object However you should be aware of how ridiculously unlikely this scenario is The SHA 1 digest is 20 bytes or 160 bits The number of randomly hashed objects needed to ensure a 5096 probability of a single collision is about 2 80 the formula for determining collision probability is p n n 1 2 1 2 160 2480 is 1 2 x 10 24 or 1 million billion billion That s 1 200 times the number of grains of sand on Earth Here s an example to give you an idea of what it would take to get a SHA 1 collision If all 6 5 billion humans on Earth were programming and every second each one was producing code that was the equiva lent of the entire Linux kernel history 1 million Git objects and pushing it into one enormous Git repository it would take 5 years until that repository contained enough objects to have a 5096 probability of a single SHA 1 object collision A higher probability exists that every member of your programming team will be attacked and killed by wolves in unrelated incidents on the same night CHAPTER 6 GIT TOOLS 145 Branch References The most straightforward way to specify a commit requires that it have a branch reference pointed at it Then you can use a branch name in any Git command that expects a commit object or SHA 1 value For instance if you want to show the last commit object on a branch the following commands are equivalent assuming that the topic1
147. at patch to generate the mbox formatted files that you can e mail to the list it turns each commit into an e mail message with the first line of the commit message as the subject and the rest of the message plus the patch that the commit introduces as the body The nice thing about this is that applying a patch from an e mail generated with format patch preserves all the commit information properly as you ll see more of in the next section when you apply these commits git format patch M origin master 0001 add limit to log function patch 0002 changed log output to 30 from 25 patch 127 128 CHAPTER 5 DISTRIBUTED GIT The format patch command prints out the names of the patch files it creates The M switch tells Git to look for renames The files end up looking like this cat 0001 add limit to log function patch From 330090432754092d704da8e76ca5c05c198e71a8 Mon Sep 17 00 00 00 2001 From Jessica Smith lt jessica example com gt Date Sun 6 Apr 2008 10 17 23 0700 Subject PATCH 1 2 add limit to log function Limit log functionality to the first 20 lib simplegit rb 2 1 files changed 1 insertions 1 deletions diff git a lib simplegit rb b lib simplegit rb index 76f47bc f9815f1 100644 a lib simplegit rb b lib simplegit rb 14 7 14 7 class SimpleGit end def log treeish master command git log treeish command git log n 20 treeish end def ls tree treeish maste
148. ate the commit was tagged and the annotation message before showing the commit information Signed Tags You can also sign your tags with GPG assuming you have a private key All you have to do is use s instead of a git tag s v1 5 m my signed 1 5 tag You need a passphrase to unlock the secret key for user Scott Chacon lt schacon gee mail com gt 1024 bit DSA key ID F721C45A created 2009 02 09 Ifyou run git show on that tag you can see your GPG signature attached to it git show v1 5 tag v1 5 Tagger Scott Chacon lt schacon gee mail com gt Date Mon Feb 9 15 22 20 2009 0800 my signed 1 5 tag BEGIN PGP SIGNATURE Version GnuPG v1 4 8 Darwin iEYEABECAAYFAkmQurIACgkOON3DxfchxFr5cACeIMN4ZxLKgg JOfoQYiOBwgySN Ki0An2JeAVUCAiJ70x6ZEtK4NvZAj82 WryJ commit 15027957951b64cf874c3557a0f3547bd83b3ff6 Merge 4a447f7 a6b4c97 Author Scott Chacon lt schacon gee mail com gt Date Sun Feb 8 19 02 46 2009 0800 Merge branch experiment A bit later you ll learn how to verify signed tags CHAPTER 2 GIT BASICS 4 Lightweight Tags Another way to tag commits is with a lightweight tag This is basically the commit checksum stored in a file no other information is kept To create a lightweight tag don t supply the a S or m option git tag v1 4 lw git tag v0 1 v1 3 V1 4 V1 4 lw V1 5 This time if you run git show on the tag you don t see the extra tag information The
149. ave to do almost no work as I covered in the last section If you want more complex access control type permissions on your repositories you can handle them with the normal filesystem permissions of the operating system your server runs If you want to place your repositories on a server that doesn t have accounts for every one on your team whom you want to have write access then you must set up SSH access for them I assume that if you have a server with which to do this you already have an SSH server installed and that s how you re accessing the server There are a few ways you can give access to everyone on your team The first is to set up accounts for everybody which is straightforward but can be cumbersome You may not want to run adduser and set temporary passwords for every user A second method is to create a single git user on the machine ask every user who is to have write access to send you an SSH public key and add that key to the ssh authorized_ keys file of your new git user At that point everyone will be able to access that machine via the git user This doesn t affect the commit data in any way the SSH user you connect as doesn t affect the commits you ve recorded Another way to do it is to have your SSH server authenticate from an LDAP server or some other centralized authentication source that you may already have set up As long as each user can get shell access on the machine any SSH authentication mechanism
150. aweb with a non lighttpd handler you can run it with the httpd option git instaweb httpd webrick 2009 02 21 10 02 21 INFO WEBrick 1 3 1 2009 02 21 10 02 21 INFO ruby 1 8 6 2008 03 03 universal darwin9 0 That starts up an HTTPD server on port 1234 and then automatically starts a web browser that opens on that page It s pretty easy on your part When you re done and want to shut down the server you can run the same command with the stop option git instaweb httpd webrick stop CHAPTER 4 GIT ON THE SERVER 91 If you want to run the web interface on a server all the time for your team or for an open source project you re hosting you ll need to set up the CGI script to be served by your normal web server Some Linux distributions have a gitweb package that you may be able to install via apt or yum so you may want to try that first I ll walk through installing GitWeb manually very quickly First you need to get the Git source code which GitWeb comes with and generate the custom CGI script git clone git git kernel org pub scm git git git cd git make GITWEB PROJECTROOT opt git prefix usr gitweb gitweb cgi sudo cp Rf gitweb var www Notice that you have to tell the command where to find your Git repositories with the GITWEB PROJECTROOT variable Now you need to make Apache use CGI for that script for which you can add a VirtualHost VirtualHost 80 ServerName gitserver DocumentRoot v
151. b4ac296e3e5b6e2a99c F44391e repo rb 100644 blob e3f094f5226292e358806b17daf78246c27c007b test txt You can then use git cat file to see how big that object is git cat file s 9bcidc421dcd51b4ac296e3e5b6e2a99cf44391e 12898 Now modify that file a little and see what happens echo testing gt gt repo rb git commit am modified repo a bit master abi1afef modified repo a bit 1 files changed 1 insertions O deletions Check the tree created by that commit and you see something interesting git cat file p master tree 100644 blob fa49b077972391ad58037050f2a75f74e3671e92 new txt 100644 blob 05408d1952634d853f09dca71d55116663690c27c repo rb 100644 blob e3f094f522629ae358806b17daf78246c27c007b test txt The blob is now a different blob which means that although you added only a single line to the end of a 400 line file Git stored that new content as a completely new object git cat file s 054084d195263d853f09dca714d55116663690c27c 12908 You have two nearly identical 12K objects on your disk Wouldn t it be nice if Git could store one of them in full but then store the second object only as the delta between it and the first It turns out that it can The initial format in which Git saves objects on disk is called a loose object format However occasionally Git packs up several of these objects into a single binary CHAPTER 9 GIT INTERNALS 237 file called a packfile in order to save space and be more effic
152. binary formats Another interesting problem you can solve this way involves diffing image files One way to do this is to run JPEG files through a filter that extracts their EXIF information metadata that is recorded with most image formats If you download and install the exiftool program you can use it to convert your images into text about the metadata so at least the diff will show you a textual representation of any changes that happened echo png diff exif gt gt gitattributes git config diff exif textconv exiftool If you replace an image in your project and run diff you see something like this diff git a image png b image png index 88839c4 4afcb7c 100644 a image png b image png 1 12 1 12 ExifTool Version Number 7 74 File Size 70 kB File Modification Date Time 2009 04 21 07 02 45 07 00 File Size 94 kB File Modification Date Time 2009 04 21 07 02 43 07 00 File Type PNG MIME Type image png Image Width 1058 Image Height 889 Image Width 1056 Image Height 827 Bit Depth 8 Color Type RGB with Alpha You can easily see that the file size and image dimensions have both changed Keyword Expansion SVN or CVS style keyword expansion is often requested by developers used to those systems The main problem with this in Git is that you can t modify a file with information about the commit after you ve committed because Git checksums the file first Howev
153. bjects 100 3 3 272 bytes done Total 3 delta 1 reused O delta O 94 CHAPTER 4 GIT ON THE SERVER To git gitserver opt git gitosis admin git fb27aec 8962da8 master gt master You can make your first push to the new iphone_project project by adding your server as a remote to your local version of the project and pushing You no longer have to manually cre ate a bare repository for new projects on the server Gitosis creates them automatically when it sees the first push git remote add origin git gitserver iphone_project git git push origin master Initialized empty Git repository in opt git iphone project git Counting objects 3 done Writing objects 100 3 3 230 bytes done Total 3 delta 0 reused O delta O To git gitserver iphone_project git new branch master master Notice that you don t need to specify the path in fact doing so won t work just a colon and then the name of the project Gitosis finds it for you You want to work on this project with your friends so you have to re add their public keys But instead of appending them manually to the ssh authorized keys file on your server you ll add them one key per file into the keydir directory How you name the keys determines how you refer to the users in the gitosis conf file Re add the public keys for John Josie and Jessica cp tmp id rsa john pub keydir john pub cp tmp id rsa josie pub keydir josie pub cp tmp id rsa j
154. ble copy of my test repository In order to do that easily you can use a tool called svnsync that comes with more recent versions of Subversion it should be distributed with at least 1 4 For these tests I created a new Subversion repository on Google code that was a partial copy of the protobuf project which is a tool that encodes structured data for network transmission To follow along you first need to create a new local Subversion repository mkdir tmp test svn svnadmin create tmp test svn Then enable all users to change revprops the easy way is to add a pre revprop change script that always exits 0 cat tmp test svn hooks pre revprop change bin sh exit 0 chmod x tmp test svn hooks pre revprop change You can now sync this project to your local machine by calling svnsync init with the to and from repositories svnsync init file tmp test svn http progit example googlecode com svn This sets up the properties to run the sync You can then clone the code by running svnsync sync file tmp test svn Committed revision 1 Copied properties for revision 1 Committed revision 2 Copied properties for revision 2 Committed revision 3 Although this operation may take only a few minutes if you try to copy the original reposi tory to another remote repository instead of a local one the process will take nearly an hour even though there are fewer than 100 commits Subversion has to clone one revision
155. blic keys of all the users who have any sort of access to your repositories one file per user The name of the file in keydir in the previous example scott pub will be different for you Gitosis takes that name from the description at the end of the public key that was imported with the gitosis init script If you look at the gitosis conf file it should only specify information about the gitosis admin project that you just cloned cat gitosis conf gitosis group gitosis admin writable gitosis admin members scott It shows you that the scott user the user with whose public key you initialized Gitosis is the only one who has access to the gitosis admin project Now you can add a new project You ll add a new section called mobile where you ll list the developers on your mobile team and projects that those developers need access to Because scott is the only user in the system right now you add him as the only member and create a new project called iphone project to start on group mobile writable iphone project members scott Whenever you make changes to the gitosis admin project you have to commit the changes and push them back up to the server in order for them to take effect git commit am add iphone project and mobile group master created 8962da8 changed name 1 files changed 4 insertions 0 deletions git push Counting objects 5 done Compressing objects 100 2 2 done Writing o
156. but it s not too difficult It s easiest to use a Linux server for it these examples use a stock Ubuntu 8 10 server Gitosis requires some Python tools so first you have to install the Python setuptools pack age which Ubuntu provides as python setuptools apt get install python setuptools Next you clone and install Gitosis from the project s main site git clone git eagain net gitosis git cd gitosis sudo python setup py install That installs a couple of executables that Gitosis will use Next Gitosis wants to put its repositories under home git which is fine But you have already set up your repositories in opt git so instead of reconfiguring everything you create a symlink 1n s opt git home git repositories Gitosis is going to manage your keys for you so you need to remove the current file re add the keys later and let Gitosis control the authorized keys file automatically For now move the authorized keys file out of the way mv home git ssh authorized keys home git ssh ak bak You need to turn your shell back on for the git user if you changed it to the git shell command People still won t be able to log in but Gitosis will control that for you So change this line in your etc passwd file git x 1000 1000 home git usr bin git shell back to this git x 1000 1000 home git bin sh Now it s time to initialize Gitosis You do this by running the gitosis init command with your pe
157. by closs lt lt self attr eccessor igit Dinery igit timeout attt eccessor igit binary git_tieecut end git mox size PII Self ait binary usr bim enw att 2009 01 30 17 49 40 2008 08 26 04 48 51 2008 08 29 10 55 31 2008 08 26 10 09 45 2008 08 23 11 00 10 2008 08 23 09 51 15 2008 08 22 14 51 56 2008 08 11 10 05 57 2008 08 10 15 04 59 2008 08 07 15 35 31 2008 08 06 11 46 51 2008 07 31 13 47 19 2008 07 31 12 52 25 WANG OF S 809986 LI EL meme uem mm be M Afin TR sna PO OM venen mewes Linen et content Venere spare change Comments Author Jos Sockus lt jos cetnock com 2009 01 30 17 49 40 gigu Figure 2 2 The gitk history visualizer You can see the commit history in the top half of the window along with a nice ancestry graph The diff viewer in the bottom half of the window shows you the changes introduced at any commit you click Undoing Things At any stage you may want to undo something Here I ll review a few basic tools for undoing changes that you ve made Be careful because you can t always undo some of these undos This is one of the few areas in Git where you may lose some work if you do it wrong Changing Your Last Commit One of the common undos takes place when you commit too early and possibly forget to add some files or you mess up your commit message If you want to try that commit again you can run commit with the amend option git commit amend
158. c branch off another topic branch Now you can fast forward your master branch see Figure 3 33 git checkout master git merge client Figure 3 33 Fast forwarding your master branch to include the client branch changes Let s say you decide to pull in your server branch as well You can rebase the server branch onto the master branch without having to check it out first by running git rebase basebranch topicbranch which checks out the topic branch in this case server for you and replays it onto the base branch master git rebase master server 74 CHAPTER 3 GIT BRANCHING This replays your server work on top of your master work as shown in Figure 3 34 Figure 3 34 Rebasing your server branch on top of your master branch Then you can fast forward the base branch master git checkout master git merge server You can remove the client and server branches because all the work is integrated and you don t need them anymore leaving your history for this entire process looking like Figure 3 35 git branch d client git branch d server Figure 3 35 Final commit history The Perils of Rebasing Ahh but the bliss of rebasing isn t without its drawbacks which can be summed up in a single line Do not rebase commits that you have pushed to a public repository If you follow that guideline you ll be fine If you don t people will hate you and you ll be scorned by fr
159. c cece eee eee 176 Colors IM GIL radere o ee i e rr reca 178 External Merge and Diff Tools ccc eee 179 Formatting and Whitespace 00 c cece eee eee 181 Server Configuration 2 0 0 ccc cc cece cence eas 183 Git AUMDULCS 055 caus cake rei xm Rr REG ERR E RONDA RENS 184 Binary Files 184 Keyword Expansion 0 00 cc ccc cece eee II 186 Exporting Your Repository 0 c cece cece eens 189 Merge Strategies 0 000 c ccc cece nen w eee ese 190 GIC HOOKS cese deret t bcr pex ERES E pb S tb a 190 Installing a HOOK 0 0 ccc ccc eee eee eens 190 Client Side Hooks 0 00 000 c eee e cence ena eaens 191 Server Side Hooks 192 xi xii CONTENTS CHAPTER 8 CHAPTER 9 An Example Git Enforced Policy 0 c cece eee e eae 193 Server Side HOOK 0 00sec eee e cence a 193 Client Side Hooks 20 0 0 200 c eee ec ee eee eee eee 199 SUMMALY 200 E a e 202 Git and Other Systems 203 Git and Subversion 0 cece cece cece ai e ee 203 gi SV 1 sc ed RD br ARM Ob WE de NS 203 Settifig Up uses doit e dre eat s t ecd ada 204 Getting Started 0 ce eee nee en en ene n wens 204 Committing Back to Subversion 0 cece eee 206 Pulling in New Changes 000 cece ee eee eee ee 207 Git Branching lssues 0 00 0 cece
160. can find at that point git config list user name Scott Chacon user email schacon gmail com color status auto color branch auto color interactive auto color diff auto You may see keys more than once because Git reads the same key from different files etc gitconfig and gitconfig for example In this case Git uses the last value for each unique key it sees You can also check what Git thinks a specific key s value is by typing git config key git config user name Scott Chacon CHAPTER 1 GETTING STARTED 13 Getting Help If you ever need help while using Git there are three ways to get the manual page manpage help for any of the Git commands git help lt verb gt git lt verb gt help man git lt verb gt For example you can get the manpage help for the config command by running git help config These commands are nice because you can access them anywhere even offline If the manpages and this book aren t enough and you need in person help you can try the git or github channel on the Freenode IRC server irc freenode net These channels are regularly filled with hundreds of people who are all very knowledgeable about Git and are often willing to help Summary You should now have a basic understanding of what Git is and how it s different from the CVCS you may have been using You should also now have a working version of Git on your system that s set up with your personal i
161. cat file p ca82a6dff817ec6644342007202690a93763949 tree cfda3bf379e4f8dba8717dee55aab78aef7f4daf parent 085bb3bcb608e1e8451d4b2432f8ecbe6306e7e7 author Scott Chacon lt schacon gmail com gt 1205815931 0700 committer Scott Chacon schaconggmail com 1240030591 0700 changed the version number Next you have two more objects to retrieve cfda3b which is the tree of content that the commit you just retrieved points to and 085bb3 which is the parent commit GET objects 08 5bb3bcb608e1e8451d4b2432f8ecbe6306e7e7 179 bytes of data That gives you your next commit object Grab the tree object GET objects cf da3bf379e4f8dba8717dee55aab78aef7f4daf 404 Not Found Oops it looks like that tree object isn t in loose format on the server so you get a 404 response back There are a couple of reasons for this the object could be in an alternate repository or it could be in a packfile in this repository Git checks for any listed alternates first GET objects info http alternates empty file If this comes back with a list of alternate URLs Git checks for loose files and packfiles there this is a nice mechanism for projects that are forks of one another to share objects on disk However because no alternates are listed in this case your object must be in a packfile To see what packfiles are available on this server you need to get the objects info packs file which contains a listing of them also generated by upda
162. cat file p d8329fc1cc938780ffdd9f94e0d364e0ea741579 100644 blob 83baae61804e65cc73a7201a7252750c76066a30 test txt You can also verify that this is a tree object git cat file t d8329fc1cc938780ffdd9f94e0d364e0ea74f579 tree You ll now create a new tree with the second version of test txt and a new file as well echo new file new txt git update index test txt git update index add new txt Your staging area now has the new version of test txt as well as the new file new txt Write out that tree recording the state of the staging area or index to a tree object and see what it looks like git write tree 0155eb4229851634a0f03eb265b69f5a2d56f341 git cat file p 0155eb4229851634a0f03eb265b69f5a2d56f341 100644 blob fa49b077972391ad58037050f2a75f74e3671e92 new txt 100644 blob 1f7a7a472abf3dd9643fd615f6da379c4acb3e3a test txt 227 228 CHAPTER 9 GIT INTERNALS Notice that this tree has both file entries and also that the test txt SHA is the version 2 SHA from earlier 1f7a7a Just for fun you ll add the first tree as a subdirectory into this one You can read trees into your staging area by calling read tree In this case you can read an existing tree into your staging area as a subtree by using the prefix option to read tree git read tree prefix bak d8329fc1cc938780ffdd9f94e0d364e0ea74f579 git write tree 3c4e9cd789d8848d89c1073707c3585e41b0e614 git cat file p 3c4e9cd789d88d8d89c1073707c3585e4
163. cat file p fdf4fc3 tree d8329fc1cc938780ffdd9f94e0d364e0ea74f579 author Scott Chacon lt schacon gmail com gt 1243040974 0700 committer Scott Chacon schaconggmail com 1243040974 0700 first commit The format for a commit object is simple it specifies the top level tree for the snapshot of the project at that point the author committer information pulled from your user name and user email configuration settings with the current timestamp a blank line and then the com mit message Next you ll write the other two commit objects each referencing the commit that came directly before it echo second commit git commit tree O155eb p fdf4fc3 cac0cab538b970a37ea1e769cbbde608743bc96d echo third commit git commit tree 3c4e9c p cacOcab 1a410efbd13591db07496601ebc7a059dd55cfe9 Each of the three commit objects points to one of the three snapshot trees you created Oddly enough you have a real Git history now that you can view with the git log command if you run it on the last commit SHA 1 git log stat 1a410e commit 1a410efbd13591db07496601ebc7a059dd55cfe9 Author Scott Chacon lt schacon gmail com gt Date Fri May 22 18 15 24 2009 0700 third commit bak test txt 1 1 files changed 1 insertions 0 deletions commit cacOcab538b970a37ea1e769cbbde608743bc96d Author Scott Chacon lt schacon gmail com gt Date Fri May 22 18 14 29 2009 0700 second commit new txt 1 test txt 2 2 files chan
164. cbe08ee5cf42e92a0289 1 2 rm git tbz2 Rewrite da3f30d019005479c99eb4c3406225613985a1db 2 2 Ref refs heads master was rewritten The index filter option is similar to the tree filter option used in Chapter 6 except that instead of passing a command that modifies files checked out on disk you re modifying your staging area or index each time Rather than remove a specific file with some thing like rm file you have to remove it with git rm cached you must remove it from the index not from disk The reason to do it this way is speed because Git doesn t have to check out each revision to disk before running your filter the process can be much much faster You can accomplish the same task with tree filter if you want The ignore unmatch option togit rmtells it not to error out if the pattern you re trying to remove isn t there Finally you ask filter branch to rewrite your history only from the 6df7640 commit up because you know that is where this problem started Otherwise it will start from the beginning and will unnec essarily take longer Your history no longer contains a reference to that file However your reflog and a new set of refs that Git added when you did the filter branch under git refs original still do so you have to remove them and then repack the database You need to get rid of anything that has a pointer to those old commits before you repack rm Rf git refs original rm Rf git logs git gc
165. ccc ccc cece eee eens 247 SUMMAE a detec ache aug aides dace tale be E A ded has ana Usb CHE 250 Creative Commons Legal Code 0 cece eee 251 xiii Foreword l April 2005 Linus Torvalds published the very first version of Git the distributed version control system that is the topic of this book and started managing the Linux kernel project with it Countless online pages have been written about Git by third parties since then but many of them are unfortunately obsolete not in the sense that the procedures they teach no longer work but in the sense that there are better ways to do the same things more effectively with more modern versions of Git The rate at which Git has undergone vast improvements both in capability and usability has been simply too rapid for those pages to keep up For along time the user manual and the documentation that came with Git were the only up to date and accurate sources of information but they were primarily written by the people who built Git The Git community sorely lacked good introductory material written from the perspective of the end user Enter Scott Chacon the author of this book who is also behind git scm com the popular online resource that has become the default home site for Git documentation In this latest book Scott makes effective use of graphics to explain the key concepts and writes in plain and clear language to give a readable overview of how to work with Git
166. ccc eee eee eee 34 Working with Remotes 0 0 c cece eee RR 35 Showing Your RemoteS 00 0 ccc eee cece e eens 35 Adding Remote Repositories 00 00 cece cece eee 36 Fetching and Pulling from Your Remotes 005 36 Pushing to Your Remotes c0 ccc eee cece eee 37 Inspecting a Remote 0 ccc cece cence 37 Removing and Renaming RemotesS 0000e eee 38 IET Em 38 Listing Your TagS 00 c ccc ccc cece eee nena es 39 Creating Tags 0 ccc ccc ccc cece ence renee es 39 Verifying TagS 0 cece ccc cece eee I 41 Tagging Later 00 ccc ccc ccc cece RII 42 Shanin T3852 rer EE NE Rn TEE 43 TIPS ANG CKS e ceci tte bte ce LR me re sib e e 43 Auto Completion 0 0 c ccc ccc cece cece eee e ees 43 Git ANAS MP 44 SUMMAN ia iod De ra bc ete dede enc a hoa n encodes 45 CHAPTER 3 CHAPTER 4 CONTENTS Git Brann siccesscnccceeueactecasencwPenseaedeeehoncstant 47 What a Branch Is 0 00 0 ccc ccc cece cence eect enes 47 Basic Branching and Merging 00 c cece eee e eee ees 53 Basic Branchilg sius ede etc eco tore a See eed 53 Basic Merging 0 0 cece cece RR 57 Basic Merge Conflicts 00 ccc cece eee eas 58 Branch Management 60 Branching Workflows sss 61 Long Running Branches 0 0 ccc ee cence ee eee 62 Topic Branches 00
167. cence e eae nka 208 Subversion Branching 00 00 cece eee eee eens 209 Subversion Commands 00000 e eee cece ences 210 Git Svn Summary 212 Migrating to Git 212 IMPONG sn araces akon nave det Sadea be ca eR e atom cage 213 dune RUE 214 A Custom Importer 0 0 0 0 0 0 0 ccc RI 216 SUMMAN eiernes cence eee ence tenes 221 Git Internals 00 00000000 ee 223 Plumbing and Porcelain 0 0 0 ccc cece eee ences 223 GIT ODJGCls en eere E UPd ed acero eases 224 Tree ODjOCtS oerni errei darane Ged sebasemaeaneaeata 226 Commit Objects eme ag exar ms 228 Object Storage 6 ccc ccc e nen 231 Git References 0 0 0 c kc ccc cee n dh nn 232 The HEAD uscire iet to gt ect iln 233 JEDE 234 ad cc EEMEUET 235 PACKS 1 ccc bepe Rp RRLER HOA RMPERIRP aik 235 The Refspac isse sessi s bem dea a 238 Pushing RefSpe Cs 0 00 00 0600000 scene eee wee ween 239 Deleting References 0 0 00 c ccc cece eee eens 240 APPENDIX CONTENTS Transfer Protocols 2 0 ccc ccc ccc cnn cece aes 240 The Dumb Protocol 0 0 c ccc cece cence aes 240 The Smart Protocol 0 0 ccc ccc ccc cence eens 242 Downloading Data 0 ccc ccc cece eee eens 243 Maintenance and Data Recovery ccc cece eee ees 244 Maintenance 0 00 c cece ee hs 244 Data RECOVEFY 0 0 06 c cence cece n 245 Removing Objects 0 0
168. companion PDF version eBook for only 10 Take the weightless companion with you anywhere W believe this Apress title will prove so indispensable that you ll want to carry it with you everywhere which is why we are offering the companion eBook in PDF format for 10 to customers who purchase this book now Convenient and fully searchable the PDF version of any content rich page heavy Apress book makes a valuable addition to your programming library You can easily find and copy code or perform examples by quickly toggling between instructions and the application Even simultaneously tackling a donut diet soda and complex code becomes simplified with hands free eBooks Once you purchase your book getting the 10 companion eBook is simple Q Visit www apress com promo tendollars Complete a basic registration form to receive a randomly generated question about this title Answer the question correctly in GO seconds and you will receive a promotional code to redeem for the 10 00 e ADICSS THE EXPERT S VOICE 2855 TELEGRAPH AVENUE SUITE 600 BERKELEY CA 94705 Book Go Wae eBookshop All Apress eBooks subject to copyright protection No part may be reproduced or transmitted in any form or by any means electronic or mechanical including photocopying recording or by any information storage or retrieval system without the prior written permission of the cop
169. congexample com 162 CHAPTER 6 GIT TOOLS git commit tree 0 else git commit tree 0 fi HEAD This goes through and rewrites every commit to have your new address Because commits contain the SHA 1 values of their parents this command changes every commit SHA in your history not just those that have the matching e mail address Debugging with Git Git also provides a couple of tools to help you debug issues in your projects Because Git is designed to work with nearly any type of project these tools are pretty generic but they can often help you hunt for a bug or culprit when things go wrong File Annotation If you track down a bug in your code and want to know when it was introduced and why file annotation is often your best tool It shows you what commit was the last to modify each line of any file So if you see that a method in your code is buggy you can annotate the file with git blame to see when each line of the method was last edited and by whom This example uses the L option to limit the output to lines 12 through 22 git blame L 12 22 simplegit rb 4832fe2 Scott Chacon 2008 03 15 10 31 28 0700 12 def show tree master 4832fe2 Scott Chacon 2008 03 15 10 31 28 0700 13 command git show tree 4832fe2 Scott Chacon 2008 03 15 10 31 28 0700 14 end 4832fe2 Scott Chacon 2008 03 15 10 31 28 0700 15 9f6560e4 Scott Chacon 2008 03 17 21 52 20 0700 16 def log tree master 79eaf55d Sc
170. cts 5 done remote Compressing objects 100 3 3 done remote Total 3 delta 1 reused 2 delta 0 Unpacking objects 100 3 3 done From git github com schacon rack 08d709f 6c5e70b master origin master Submodule path rack checked out 6c5e70b984a60b3cecd395edd5b48a7575bf58e0 You have to do this every time you pull down a submodule change in the main project It s strange but it works One common problem happens when a developer makes a change locally in a submodule but doesn t push it to a public server Then they commit a pointer to that non public state and push up the superproject When other developers try to run git submodule update the submodule system can t find the commit that is referenced because it exists only on the first developer s system If that happens you see an error like this git submodule update fatal reference isn t a tree 6c5e70b984a60b3cecd395edd5b48a7575bf58e0 Unable to checkout 6c5e70b984a60b3cecd395edd5ba7575bf58e0 in submodule path rack CHAPTER 6 GIT TOOLS 169 You have to see who last changed the submodule git log 1 rack commit 85a3eee996800fcfa91e2119372dd4172bf76678 Author Scott Chacon lt schacon gmail com gt Date Thu Apr 9 09 19 14 2009 0700 added a submodule reference I will never make public hahahahaha Then you e mail that guy and yell at him Superprojects Sometimes developers want to get a combination of a large project s subdirectories depend in
171. cts on disk before you ran the gc were collectively about 12K in size the new packfile is only 6K You ve halved your disk usage by packing your objects How does Git do this When Git packs objects it looks for files that are named and sized similarly and stores just the deltas from one version of the file to the next You can look into the packfile and see what Git did to save space The git verify pack plumbing command allows you to see what was packed up git verify pack v pack 7a16e4488ae40c7d2bc56ea2bd43e25212a66c45 idx 0155eb4229851634a0f03eb265b69f5a2d56f341 tree 71 76 5400 05408d195263d853f09dca71d55116663690c27c blob 12908 3478 874 09f01cea547666f58d6a84d809583841a7c6f0130 tree 106 107 5086 1a410efbd13591db07496601ebc7a059dd55cfe9 commit 225 151 322 1f7a7a472abf3dd9643fd615f6da379c4acb3e3a blob 10 19 5381 3c4e9cd789d88d8d89c1073707c3585e41b0e614 tree 101 105 5211 484a59275031909e19aadb7c92262719cfcdf19a commit 226 153 169 83baae61804e65cc73a7201a7252750c76066a30 blob 10 19 5362 9585191f37f7b0fb9444f35a9bfS5Odei191beadc2 tag 136 127 5476 9bc1dc421dcd51b4ac296e3e5b6e2a99cf44391e blob 7 18 5193 1 05408d195263d853f09dca71d55116663690c27c abiafef80fac8e34258ff41fc1b867c702daa24b commit 232 157 12 CacOcab538b970a37ea1e769cbbde608743bc96d commit 226 154 473 238 CHAPTER 9 GIT INTERNALS d8329fc1cc938780ffdd9f94e0d364e0ea74f579 tree 36 46 5316 e3f094f522629ae358806b17daf78246c27c007b blob 1486 734 4352 f8f51d7d821760462eca26eebafde32087
172. d allows only certain users to modify certain subdirectories in a project You ll build client scripts that help the developer know if their push will be rejected and server scripts that actually enforce the policies I used Ruby to write these both because it s my preferred scripting language and because Ifeelit s the most pseudocode looking of the scripting languages thus you should be able to roughly follow the code even if you don t use Ruby However any language will work fine All the sample hook scripts distributed with Git are in either Perl or Bash scripting so you can also see plenty of examples of hooks in those languages by looking at the samples Server Side Hook All the server side work will go into the update file in your hooks directory The update file runs once per branch being pushed and takes the reference being pushed to the old revision where that branch was and the new revision being pushed You also have access to the user doing the pushing if the push is being run over SSH If you ve allowed everyone to connect with a single user like git via public key authentication you may have to give that user a shell wrapper that determines which user is connecting based on the public key and set an environment variable specifying that user Here I assume the connecting user is in the USER environment variable so your update script begins by gathering all the information you need it usr bin env ruby refname ARGV O
173. d4b536e7479fe34593e72e6c6c1819e53b Author Scott Chacon lt schacon gmail com gt Date Thu Dec 11 14 58 32 2008 0800 added some blame and merge stuff In this case choose 1c002dd If you git show that commit the following commands are equivalent assuming the shorter versions are unambiguous git show 1c002dd4b536e7479fe34593e72e6c6c1819e53b git show 1c002dd4b536e7479f git show 1c002d Git can figure out a short unique abbreviation for your SHA 1 values If you pass abbrev commit to the git log command the output will use shorter values but keep them unique it defaults to using seven characters but makes them longer if necessary to keep the SHA 1 unambiguous git log abbrev commit pretty oneline ca82a6d changed the version number 085bb3b removed unnecessary test code allbefo first commit Generally eight to ten characters are more than enough to be unique within a project One of the largest Git projects the Linux kernel is beginning to need 12 characters out of the possible 40 to stay unique A SHORT NOTE ABOUT SHA 1 A lot of people become concerned at some point that they will by random happenstance have two objects in their repository that hash to the same SHA 1 value What then If you do happen to commit an object that hashes to the same SHA 1 value as a previous object in your repository Git will see the previous object in your Git database and assume it was already written If you try to check out th
174. daemon you have to run this on each project you want the Git daemon to serve cd path to project git touch git daemon export ok The presence of that file tells Git that it s OK to serve this project without authentication Gitosis can also control which projects GitWeb shows First you need to add something like the following to the etc gitweb conf file projects list home git gitosis projects list projectroot home git repositories export ok git daemon export ok Qgit base url list git gitserver You can control which projects GitWeb lets users browse by adding or removing a gitweb setting in the Gitosis configuration file For instance if you want the iphone project to show up on GitWeb you make the repo setting look like this repo iphone project daemon yes gitweb yes Now if you commit and push the project GitWeb will automatically start showing your iphone project Hosted Git If you don t want to go through all the work involved in setting up your own Git server you have several options for hosting your Git projects on an external dedicated hosting site Doing so offers a number of advantages a hosting site is generally quick to set up and easy to start projects on and no server maintenance or monitoring is involved Even if you set up and run your own server internally you may still want to use a public hosting site for your open source code it s generally easier for the open so
175. dentity It s now time to learn some Git basics CHAPTER 2 Git Basics l you can read only one chapter to get going with Git this is it This chapter covers every basic command you need to do the vast majority of the things you ll eventually spend your time doing with Git By the end of the chapter you should be able to configure and initialize a repository begin and stop tracking files and stage and commit changes I ll also show you how to set up Git to ignore certain files and file patterns how to undo mistakes quickly and easily how to browse the history of your project and view changes between commits and how to push and pull from remote repositories Getting a Git Repository You can get a Git project using two main approaches The first takes an existing project or directory and imports it into Git The second clones an existing Git repository from another server Initializing a Repository in an Existing Directory If you re starting to track an existing project in Git you need to go to the project s directory and type git init This command creates a new subdirectory named git that contains all of your necessary repository files a Git repository skeleton At this point nothing in your project is tracked yet See Chapter 9 for more information about exactly what files are contained in the git direc tory you just created If you want to start version controlling existing files as opposed to an empty directory you
176. don t code for a whole weekend on five different issues and then submit them all as one massive commit on Monday Even if you don t commit during the weekend use the staging area on Monday to split your work into at least one commit per issue with a useful message per commit If some of the changes modify the same file try to use git add patch to partially stage files covered in detail in Chapter 6 The project snapshot at the tip of the branch is identical whether you do one commit or five as long as all the changes are added at some point so try to make things easier on your fellow developers when they have to review your changes This approach also makes it easier to pull out or revert one of the chang esets if you need to later Chapter 6 describes a number of useful Git tricks for rewriting history and interactively staging files you can use these tools to help craft a clean and understand able history The last thing to keep in mind is the commit message Getting in the habit of creating quality commit messages makes using and collaborating with Git a lot easier As a general rule your messages should start with a single line that s no more than about 50 characters and that describes the changeset concisely followed by a blank line followed by a more detailed expla nation The Git project requires that the more detailed explanation include your motivation for 112 CHAPTER 5 DISTRIBUTED GIT the change and contrast its implementati
177. ds a cinematographic work to which are assimilated works expressed by a process analogous to cinematography a work of drawing painting architecture sculpture engraving or lithography a photographic work to which are assimilated works expressed by a process analogous to photography a work of applied art an illustration map plan sketch or three dimensional work relative to geography topography architecture or science a performance a broadcast a pho nogram a compilation of data to the extent it is protected as a copyrightable work or a work performed by a variety or circus performer to the extent it is not other wise considered a literary or artistic work APPENDIX CREATIVE COMMONS LEGAL CODE 253 h You means an individual or entity exercising rights under this License who has not previously violated the terms of this License with respect to the Work or who has received express permission from the Licensor to exercise rights under this License despite a previous violation i Publicly Perform means to perform public recitations of the Work and to com municate to the public those public recitations by any means or process including by wire or wireless means or public digital performances to make available to the public Works in such a way that members of the public may access these Works from a place and at a place individually chosen by them to perform the Work to the public by any means or process and the commu
178. e or called from scripts These commands are generally referred to as plumbing commands and the more user friendly commands are called porcelain commands The book s first eight chapters deal almost exclusively with porcelain commands But in this chapter you ll be dealing mostly with the lower level plumbing commands because they give you access to the inner workings of Git and help demonstrate how and why Git does what it does These commands aren t meant to be used manually on the command line but rather to be used as building blocks for new tools and custom scripts When you run git init in a new or existing directory Git creates the git directory which is where almost everything that Git stores and manipulates is located If you want to back up or clone your repository copying this single directory elsewhere gives you nearly 223 224 CHAPTER 9 GIT INTERNALS everything you need This entire chapter basically deals with the stuff in this directory Here s what it looks like ls HEAD branches config description hooks index info objects refs You may see some other files in there but this is a fresh git init repository it s what you see by default The branches directory isn t used by newer Git versions and the description file is only used by the GitWeb program so don t worry about those The config file contains your project specific configuration options and the info directory keeps a global exclude file f
179. e URL r Who has access to this repository You can change this later e Anyone learn more about public repos Upgrade your plan to create more private repositories Create Repository Figure 4 5 Creating a new repository on GitHub All you really have to do is provide a project name but you can also add a description When that is done click the Create Repository button Now you have a new repository on GitHub see Figure 4 6 github Search testinguser ee cte og ol SOCIAL CODING Browse Guides Advanced 0 dashboard gists testinguser iphone project edit Ge unwatch DE Description iphone project for our mobile group edit Homepage Click to edit edit Public Clone URL git github com testinguser phone_projectgit is Your Clone URL git amp github com testinguser iphone project git E Figure 4 6 GitHub project header information 100 CHAPTER 4 GIT ON THE SERVER Because you have no code there yet GitHub shows you instructions for how to create a brand new project push up an existing Git project or import a project from a public Subver sion repository see Figure 4 7 Global setup Download and install Git git config global user email test github com Next steps mkdir iphone_project cd iphone_project git init touch README git add README git commit m first commit git remote add origin git github com testinguser iphone_project git git push origin ma
180. e last two commits In fact you can do n where nis any integer to show the last n commits In reality you re unlikely to use that often because Git by default pipes all output through a pager so you see only one page oflog output at a time However the time limiting options such as since and until are very useful For example this command gets the list of commits made in the last two weeks git log since 2 weeks CHAPTER 2 GIT BASICS 31 This command works with lots of formats you can specify a specific date 2008 01 15 or a relative date such as 2 years 1 day 3 minutes ago You can also filter the list to commits that match some search criteria The author option allows you to filter on a specific author and the grep option lets you search for key words in the commit messages Note that if you want to specify both author and grep options you have to add all match or the command will match commits with either The last really useful option to pass to git log asa filter is a path If you specify a directory or file name you can limit the log output to commits that introduced a change to those files This is always the last option and is generally preceded by double dashes to separate the paths from the options In Table 2 3 I list these and a few other common options for your reference Table 2 3 Common git log Filtering Options Option Description n Show only the last n commits since
181. e that to whatever your stable published branch is After you run a successful git checkout the post checkout hook runs you can use it to set up your working directory properly for your project environment This may mean moving in large binary files that you don t want source controlled auto generating documentation or something along those lines Finally the post merge hook runs after a successful merge command You can use it to restore data in the working tree that Git can t track such as permissions data This hook can likewise validate the presence of files external to Git control that you may want copied in when the working tree changes Server Side Hooks In addition to the client side hooks you can use a couple of important server side hooks as a system administrator to enforce nearly any kind of policy for your project These scripts run before and after pushes to the server The pre hooks can exit non zero at any time to reject the push as well as print an error message back to the client you can set up a push policy that s as complex as you wish pre receive and post receive The first script to run when handling a push from a client is pre receive It takes a list of references that are being pushed from stdin if it exits non zero none of them are accepted You can use this hook to do things like make sure none of the updated references are non fast forwards or to check that the user doing the pushing has create delete
182. e work again into a new merge commit Summary I ve covered basic branching and merging in Git You should feel comfortable creating and switching to new branches switching between branches and merging local branches together You should also be able to share your branches by pushing them to a shared server working with others on shared branches and rebasing your branches before they re shared CHAPTER 4 Git on the Server A this point you should be able to do most of the day to day tasks for which you ll be using Git However in order to do any collaboration in Git you ll need to have a remote Git repository Although you can technically push change to and pull changes from individuals repositories doing so is discouraged because you can fairly easily confuse what they re work ing on if you re not careful Furthermore you want your collaborators to be able to access the repository even if your computer is offline having a more reliable common repository is often useful Therefore the preferred method for collaborating with someone is to set up an intermediate repository that you both have access to and push to and pull from that I ll refer to this repository as a Git server but you ll notice that it generally takes a tiny amount of resources to host a Git repo so you ll rarely need to use an entire server for it Running a Git server is simple First you choose which protocols you want your server to communicate with The f
183. ece cece cece tence eens 142 SUMMAN i aaea eiit etude e 142 Git 1 TETUER 143 Revision Selection 0 c ccc ccc cece cence eee ee eens 143 Single Revisions 143 Commit Ranges 000s ccc ccc cece eee eee ees 147 CHAPTER 7 CONTENTS Interactive Staging 0 ccc ccc cece eee ees 150 SA SNINO 2e order terne Editi teen dodi ate hte tains 153 Stashing Your Work 2 0 0 0 0c cc cece cece eee ences 154 Creating a Branch from a Stash 0 0 cece eee ees 156 Rewriting History 0 c ccc ccc RR 156 Changing the Last Commit esee 156 Changing Multiple Commit Messages ssuseuee 157 Reordering Commits 00 0 0 c cece eee eee 158 Squashing a Commit 00 0 c ccc cece eee aes 159 Splitting a Commit 160 The Nuclear Option filter branch lsssuesussssssse 160 Debugging with Git 162 File Annotation 20 00 e ees 162 Binary Searcli nee etie chr canc neers 163 Submodules 0 see 165 Starting with Submodules 00 c cece cece eae 165 Cloning a Project with Submodules 05 167 Superprojects e n eni aaa e IIR mnn 169 Issues with Submodules n nannan 169 Subtree Merging 0 0 0 ccc cece ccc eee e ence ens 171 NILUS 173 Customizing Git aa 175 Git Configuration sssssssssssss RR 175 Basic Client Configuration 00 cc
184. ect and the last commit date was automatically injected into it when git archive ran you can set up the file like this echo Last commit date Format cd gt LAST COMMIT echo LAST COMMIT export subst gitattributes git add LAST COMMIT gitattributes git commit am adding LAST COMMIT file for archives 190 CHAPTER 7 CUSTOMIZING GIT When yourun git archive the contents of that file when people open the archive file will look like this cat LAST COMMIT Last commit date Format Tue Apr 21 08 38 48 2009 0700 Merge Strategies You can also use Git attributes to tell Git to use different merge strategies for specific files in your project One very useful option is to tell Git to not try to merge specific files when they have conflicts but rather to use your side of the merge over someone else s This is helpful if a branch in your project has diverged or is specialized but you want to be able to merge changes back in from it and you want to ignore certain files Say you have a database settings file called database xml that is different in two branches and you want to merge in your other branch without messing up the database file You can set up an attribute like this database xml merge ours If you merge in the other branch instead of having merge conflicts with the database xml file you see something like this git merge topic Auto merging database xml Merge made by recursive In this case
185. ed 2 files changed 3 insertions 0 deletions create mode 100644 README 24 CHAPTER 2 GIT BASICS Now you ve created your first commit The commit has given you some output about itself which branch you committed to master what SHA 1 checksum the commit has 463dc4f how many files were changed and statistics about lines added and removed in the commit Remember that the commit records the snapshot you set up in your staging area Any thing you didn t stage is still sitting there modified you can do another commit to add it to your history Every time you perform a commit you re recording a snapshot of your project that you can revert to or compare to later Skipping the Staging Area Although it can be amazingly useful for crafting commits exactly how you want them the staging area is sometimes a bit more complex than you need in your workflow If you want to skip the staging area Git provides a simple shortcut Providing the a option to the git comnit command makes Git automatically stage every file that is already tracked before doing the commit letting you skip the git add part git status On branch master Changed but not updated modified benchmarks rb git commit a m added new benchmarks master 83e38c7 added new benchmarks 1 files changed 5 insertions 0 deletions Notice how you don t have to run git add on the benchmarks rb file in this case before you commit Re
186. ed README txt modified benchmarks rb He OH HE HE Right below the Changes to be committed text it says use git reset HEAD lt file gt to unstage So let s use that advice to unstage the benchmarks rb file git reset HEAD benchmarks rb benchmarks rb locally modified git status On branch master Changes to be committed use git reset HEAD lt file gt to unstage modified README txt Changed but not updated use git add lt file gt to update what will be committed 34 CHAPTER 2 GIT BASICS use git checkout lt file gt to discard changes in working directory modified benchmarks rb The command is a bit strange but it works The benchmarks rb file is modified but once again unstaged Unmodifying a Modified File What if you realize that you don t want to keep your changes to the benchmarks rb file How can you easily unmodify it revert it back to what it looked like when you last committed or initially cloned or however you got it into your working directory Luckily git status tells you how to do that too In the last example output the unstaged area looks like this Changed but not updated use git add lt file gt to update what will be committed use git checkout lt file gt to discard changes in working directory modified benchmarks rb It tells you pretty explicitly how to discard the changes you
187. ed tags tags created with the a or s flag so release tags should be created this way if you re using git describe to ensure the commit is named properly when described You can also use this string as the target of a checkout or show command although it relies on the abbreviated SHA 1 value at the end so it may not be valid forever For instance the Linux kernel recently jumped from 8 to 10 characters to ensure SHA 1 object uniqueness so oldergit describe output names were invalidated Preparing a Release Now you want to release a build One of the things you ll want to do is create an archive of the latest snapshot of your code for those poor souls who don t use Git The command to do this is git archive git archive master prefix project gzip gt git describe master tar gz 1s tar gz V1 6 2 rc1 20 g8c5b85c tar gz If someone opens that tarball they get the latest snapshot of your project under a proj ect directory You can also create a zip archive in much the same way but by passing the format zip option to git archive git archive master prefix project format zip gt git describe master zip You now have a nice tarball and a zip archive of your project release that you can upload to your website or e mail to people 142 CHAPTER 5 DISTRIBUTED GIT The Shortlog It s time to e mail your mailing list of people who want to know what s happening in your project A nice way of quickly getti
188. ed workflow Integration Manager Workflow Because Git allows you to have multiple remote repositories it s possible to have a workflow where each developer has write access to their own public repository and read access to every one else s This scenario often includes a canonical repository that represents the official project To contribute to that project you create your own public clone of the project and push your changes to it Then you can send a request to the maintainer of the main project to pull in your changes They can add your repository as a remote test your changes locally merge them into their branch and push back to their repository The process works as follows see Figure 5 2 The project maintainer pushes to their public repository Acontributor clones that repository and makes changes The contributor pushes to their own public copy 1 2 3 4 The contributor sends the maintainer an e mail asking them to pull changes 5 The maintainer adds the contributor s repo as a remote and merges locally 6 The maintainer pushes merged changes to the main repository This is a very common workflow with sites like GitHub where it s easy to fork a project and push your changes into your fork for everyone to see One of the main advantages of this approach is that you can continue to work and the maintainer of the main repository can pull in your changes at any time Contributors don t have to wait for the
189. een taken in the preparation of this work neither the author s nor Apress shall have any liability to any person or entity with respect to any loss or damage caused or alleged to be caused directly or indi rectly by the information contained in this work The source code for this book is available to readers at http www apress com I would like to dedicate this my first print book to my little girl Josephine whose release date was nearly the same as this book s Contents at a Glance POPC WOM 5 iint datei a tabe Dori a a Diui take Gla end stadi odeie N xv About the AUNO incre lerra b RR REpR RD RR ABIT Yep REF dd ds xvii About the Technical Reviewer lsssssssssssssssssRRIRRRR e xviii Acknowledgments 0 00000 c cece cece Ihn xix INTODUGUON 24 2 24 cathedetcanavedtentehekewasa be deeaeasena tara sokesanaeeds Mack hens xxi CHAPTER 1 Getting Started ii c2545nodcaceonenderascerenneeeanSadasuenoasiese 1 CHAPTER 2 LC 1 fo a eee On Peg ern 15 CHAPTER 3 Git Branching ria orn opa ko PUR RARE bLRNMPe POLEST IR ATUS da 47 CHAPTER 4 Git on the Server oo vce deca a rodar aor DER LER Rene Rae 79 CHAPTER 5 Distributed Git usieiuiuea Le ae YER ROME EE E ERE dd 107 CHAPTER 6 Git FOOIS etter ee a ede an a eo EA 143 CHAPTER 7 Customizing DIL eonim pex dada iQe E RE EERDLEDORSA a dux 175 CHAPTER 8 Git and Other Systems ssuuuuuuuuuuesueseeueese 203 CHAPTER 9 Git MEM gn ERR T 223 APPENDIX Creative Commons
190. eleting a reference you would see the opposite all 0s on the right side Git sends a line for each reference you re updating with the old SHA the new SHA and the reference that is being updated The first line also has the client s capabilities Next the client uploads a packfile of all the objects the server doesn t have yet Finally the server responds with a success or failure indication oooAunpack ok Downloading Data When you download data the fetch pack and upload pack processes are involved The client initiates a fetch pack process that connects to an upload pack process on the remote side to negotiate what data will be transferred down There are different ways to initiate the upload pack process on the remote repository You can run via SSH in the same manner as the receive pack process You can also initiate the process via the Git daemon which listens on a server on port 9418 by default The fetch pack process sends data that looks like this to the daemon after connecting 003fgit upload pack schacon simplegit progit gitNVohost myserver comNO It starts with the 4 bytes specifying how much data is following then the command to run followed by a null byte and then the server s hostname followed by a final null byte The Git daemon checks that the command can be run and that the repository exists and has public permissions If everything is cool it fires up the upload pack process and hands off the request to it If you
191. ems CVS Subversion Perforce Bazaar and so on think of the information they keep as a set of files and the changes made to each file over time as illus trated in Figure 1 4 Checkins over Time Figure 1 4 Other systems tend to store data as changes to a base version of each file Git doesn t think of or store its data this way Instead Git thinks of its data more like a set of snapshots of a mini filesystem Every time you commit or save the state of your project in Git it basically takes a picture of what all your files look like at that moment and stores a ref erence to that snapshot To be efficient if files have not changed Git doesn t store the file again just a link to the previous identical file it has already stored Git thinks about its data more like Figure 1 5 Checkins over Time Figure 1 5 Git stores data as snapshots of the project over time This is an important distinction between Git and nearly all other VCSs It makes Git recon sider almost every aspect of version control that most other systems copied from the previous generation This makes Git more like a mini filesystem with some incredibly powerful tools built on top of it rather than simply a VCS We ll explore some of the benefits you gain by thinking of your data this way when we cover Git branching in Chapter 3 CHAPTER 1
192. ent branch to the same commit as the branch you are rebasing onto and finally applying each change in turn Figure 3 29 illustrates this process f experiment CUI X ES Figure 3 29 Rebasing the change introduced in C3 onto C4 At this point you can go back to the master branch and do a fast forward merge see Figure 3 30 Figure 3 30 Fast forwarding the master branch Now the snapshot pointed to by C3 is exactly the same as the one that was pointed to by C5 in the merge example There is no difference in the end product of the integration but rebasing makes for a cleaner history If you examine the log of a rebased branch it looks like a linear history it appears that all the work happened in series even when it originally hap pened in parallel 72 CHAPTER 3 GIT BRANCHING Often you ll do this to make sure your commits apply cleanly on a remote branch perhaps in a project to which you re trying to contribute but that you don t maintain In this case you d do your work in a branch and then rebase your work onto origin master when you were ready to submit your patches to the main project That way the maintainer doesn t have to do any inte gration work just a fast forward or a clean apply Note that the snapshot pointed to by the final commit you end up with whether it s the last of the rebased commits for a rebase or the final merge commit after a merge is the same snaps
193. er you can inject text into a file when it s checked out and remove it again before it s added to a commit Git attributes offers you two ways to do this First you can inject the SHA 1 checksum of a blob into an Id field in the file automati cally If you set this attribute on a file or set of files then the next time you check out that branch Git will replace that field with the SHA 1 of the blob It s important to notice that it isn t the SHA of the commit but of the blob itself CHAPTER 7 CUSTOMIZING GIT 187 echo txt ident gt gt gitattributes echo Id gt test txt The next time you check out this file Git injects the SHA of the blob rm text txt git checkout text txt cat test txt Id 42812b7653c7b88933f8a9d6cad0ca16714b9bb3 However that result is of limited use If you ve used keyword substitution in CVS or Sub version you can include a datestamp the SHA isn t all that helpful because it s fairly random and you can t tell if one SHA is older or newer than another It turns out that you can write your own filters for doing substitutions in files on commit checkout These are the clean and smudge filters In the gitattributes file you can set a filter for particular paths and then set up scripts that will process files just before they re committed clean see Figure 7 2 and just before they re checked out smudge see Figure 7 3 These filters ca
194. erver featureA Server featureBee Jessica John Josie Server featureA Server featureBee Figure 5 15 Basic sequence of this managed team workflow 124 CHAPTER 5 DISTRIBUTED GIT Public Small Project Contributing to public projects is a bit different Because you don t have the permissions to directly update branches on the project you have to get the work to the maintainers some other way This first example describes contributing via forking on Git hosts that support easy forking The repo or cz and GitHub hosting sites both support this and many project main tainers expect this style of contribution The next section deals with projects that prefer to accept contributed patches via e mail First you ll probably want to clone the main repository create a topic branch for the patch or patch series you re planning to contribute and do your work there The sequence looks basically like this git clone url cd project git checkout b featureA work git commit work git commit You may want to use rebase ito squash your work down to a single commit or rearrange the work in the commits to make the patch easier for the maintainer to review see Chapter 6 for more information about interactive rebasing When your branch work is finished and you re ready to contribute it back to the maintain ers go to the original project page and click the Fork button creating your own writable fork of the pr
195. es To create an index with a single entry the first version of your text txt file you can use the plumbing command update index You use this com mand to artificially add the earlier version of the test txt file to a new staging area You must pass it the add option because the file doesn t yet exist in your staging area you don t even have a staging area set up yet and cacheinfo because the file you re adding isn t in your directory but is in your database Then you specify the mode SHA 1 and filename git update index add cacheinfo 100644 83baae61804e65cc73a7201a7252750c76066a30 test txt In this case you re specifying a mode of 100644 which means it s a normal file Other options are 100755 which means it s an executable file and 120000 which specifies a sym bolic link The mode is taken from normal UNIX modes but is much less flexible these three CHAPTER 9 GIT INTERNALS modes are the only ones that are valid for files in Git although other modes are used for direc tories and submodules README Rakefile lib Y g simplegit rb p Figure 9 1 Simple version of the Git data model Now you can use the write tree command to write the staging area out to a tree object No w option is needed calling write tree automatically creates a tree object from the state of the index if that tree doesn t yet exist git write tree d8329fc1cc938780ffdd9f94e0d364e0ea74f579 git
196. essica pub keydir jessica pub Now you can add them all to your mobile team so they have read and write access to iphone project group mobile writable iphone project members scott john josie jessica After you commit and push that change all four users will be able to read from and write to that project Gitosis has simple access controls as well If you want John to have only read access to this project you can do this instead group mobile writable iphone project members scott josie jessica group mobile ro readable iphone project members john Now John can clone the project and get updates but Gitosis won t allow him to push back up to the project You can create as many of these groups as you want each containing different CHAPTER 4 GIT ON THE SERVER 95 users and projects You can also specify another group as one of the members to inherit all of its members automatically If you have any issues it may be useful to add loglevel DEBUG under the gitosis sec tion If you ve lost push access by pushing a messed up configuration you can manually fix the file on the server under home git gitosis conf the file from which Gitosis reads its info A push to the project takes the gitosis conf file you just pushed up and sticks it there If you edit that file manually it remains like that until the next successful push to the gitosis admin project Git Daemon For public unauthenticated read access
197. f your project s git directory contains a copy of the ACL file you used previously then the fol lowing pre commit script will enforce those constraints for you usr bin env ruby user ENV USER insert acl access data method from above only allows certain users to modify certain subdirectories in a project def check directory perms access get acl access data git acl files modified git diff index cached name only HEAD split Mn files modified each do path next if path size has file access false access user each do access path if laccess path path index access path O has file access true end if has file access puts POLICY You do not have access to push to path exit 1 end end end check directory perms This is roughly the same script as the server side part but with two important differences First the ACL file is in a different place because this script runs from your working directory not from your Git directory You have to change the path to the ACL file from this access get acl access data acl to this access get acl access data git acl The other important difference is the way you get a listing of the files that have been changed Because the server side method looks at the log of commits and at this point the commit hasn t been recorded yet you must get your file listing from the staging area instead Instead of files modified git log 1
198. f the Git project tends to namespace these branches as well such as sc ruby client where sc is short for the person who contributed the work As you ll remember you can create the branch based off your master branch like this git branch sc ruby client master Or if you want to also switch to it immediately you can use the checkout b option git checkout b sc ruby client master Now you re ready to add your contributed work into this topic branch and determine if you want to merge it into your longer term branches Applying Patches from E mail If you receive a patch over e mail that you need to integrate into your project you need to apply the patch in your topic branch to evaluate it There are two ways to apply an e mailed patch with git apply or with git am Applying a Patch with apply If you received the patch from someone who generated it with the git diff or a Unix diff command you can apply it with the git apply command Assuming you saved the patch at tmp patch ruby client patch you can apply the patch like this git apply tmp patch ruby client patch This modifies the files in your working directory It s almost identical to running a patch p1 command to apply the patch although it s more paranoid and accepts fewer fuzzy matches then patch It also handles file adds deletes and renames if they re described in the git diff format which patch won t do Finally git apply is an apply all or abort all model w
199. f you want to keep the experiment branch up to date and preview what you re about to merge in Another very frequent use of this syntax is to see what you re about to push to a remote git log origin master HEAD This command shows you any commits in your current branch that aren t in the master branch on your origin remote If you run agit push and your current branch is tracking origin master the commits listed by git log origin master HEAD are the commits that will be transferred to the server You can also leave off one side of the syntax to have Git assume HEAD For example by typing git log origin master you can get the same results as in the previous example Git substitutes HEAD if one side is missing CHAPTER 6 GIT TOOLS 149 Multiple Points The double dot syntax is useful as shorthand but perhaps you want to specify more than two branches to indicate your revision such as seeing what commits are in any of several branches that aren t in the branch you re currently on Git allows you to do this by using either the character or not before any reference from which you don t want to see reachable commits Thus these three commands are equivalent git log refA refB git log refA refB git log refB not refA This is nice because with this syntax you can specify more than two references in your query which you can t do with the double dot syntax For instance if you want to see all com mits that are reachable f
200. fault on every push This is a relatively expensive operation and may add a lot of time to each push depending on the size of the repo or the push If you want Git to check object consistency on every push you can force it to do so by setting receive fsckObjects to true git config system receive fsckObjects true Now Git will check the integrity of your repository before each push is accepted to make sure faulty clients aren t introducing corrupt data receive denyNonFastForwards If you rebase commits that you ve already pushed and then try to push again or otherwise try to push a commit to a remote branch that doesn t contain the commit that the remote branch currently points to you ll be denied This is generally good policy but in the case of the rebase you may determine that you know what you re doing and can force update the remote branch with a f flag to your push command To disable the ability to force update remote branches to non fast forward references set receive denyNonFastForwards git config system receive denyNonFastForwards true The other way you can do this is via server side receive hooks which I ll cover in a bit That approach lets you do more complex things like deny non fast forwards to a certain sub set of users receive denyDeletes One of the workarounds to the denyNonFastForwards policy is for the user to delete the branch and then push it back up with the new reference In newer versions
201. fbd13591db07496601ebc7a059dd55cfe9 updating HEAD abiafef HEAD 1 abi1afef80fac8e34258ff41fc1b867c702daa24b updating HEAD Here you can see the two commits you checked out but there isn t much information To see the same information in a much more useful way you can run git log g which provides normal log output for your reflog git log g commit 1a410efbd13591db07496601ebc7a059dd55cfe9 Reflog HEAD o Scott Chacon lt schacon gmail com gt Reflog message updating HEAD Author Scott Chacon lt schacon gmail com gt Date Fri May 22 18 22 37 2009 0700 third commit commit ab1afef80fac8e34258ff41fc1b867c702daa24b Reflog HEAD 1 Scott Chacon lt schacon gmail com gt Reflog message updating HEAD Author Scott Chacon lt schacon gmail com gt Date Fri May 22 18 15 24 2009 0700 modified repo a bit It looks like the bottom commit is the one you lost so you can recover it by creating a new branch at that commit For example you can start a branch named recover branch at that commit ab1afef git branch recover branch abiafef git log pretty oneline recover branch abiafef80fac8e34258ff41fc1b867c702daa24b modified repo a bit 484a59275031909e19aadb7c92262719cfcdfi9a added repo rb 1a410efbd13591db07496601ebc7a059dd55cfe9 third commit cac0cab538b970a37ea1e769cbbde608743bc96d second commit fdf4fc3344e67ab0681836878b6c4951e3b15f3d first commit Cool now you have a branch named recover branch that is where your m
202. force you should look for an importer online quality importers are available for CVS Clear Case Visual Source Safe even a directory of archives If none of these tools works for you you have a rarer tool or you otherwise need a more custom importing process you should use git fast import This command reads simple instructions from stdin to write specific Git data It s much easier to create Git objects this way than to run the raw Git commands or try to write the raw objects see Chapter 9 for more information This way you can write an import script that reads the necessary information out of the sys tem you re importing from and prints straightforward instructions to stdout You can then run this program and pipe its output through git fast import To quickly demonstrate you ll write a simple importer Suppose you work in current you back up your project by occasionally copying the directory into a time stamped back YYYY MM DD backup directory and you want to import this into Git Your directory structure looks like this ls opt import from back 2009 01 02 back 2009 01 04 back 2009 01 14 back 2009 02 03 current In order to import a Git directory you need to review how Git stores its data As you may remember Git is fundamentally a linked list of commit objects that point to a snapshot of con tent All you have to do is tell fast import what the content snapshots are what commit data points to them and the order they go
203. from back 2009 01 O4from 1 deleteall M 644 inline file rb data 14 version three M 644 inline new rb data 16 new version one 220 CHAPTER 8 GIT AND OTHER SYSTEMS To run the importer pipe this output through git fast import while in the Git directory you want to import into You can create a new directory and then run git init in it for a start ing point and then run your script git init Initialized empty Git repository in opt import_to git ruby import rb opt import_from git fast import git fast import statistics Alloc d objects 5000 Total objects 18 1 duplicates blobs 7 1 duplicates 0 deltas trees 6 o duplicates 1 deltas commits 5 o duplicates o deltas tags o o duplicates 0 deltas Total branches 1 1 loads marks 1024 5 unique atoms 3 Memory total 2255 KiB pools 2098 KiB objects 156 KiB pack report getpagesize 4096 pack report core packedGitWindowSize 33554432 pack report core packedGitLimit 268435456 pack report pack used ctr 9 pack_report pack_mmap calls 5 pack_report pack_open_windows 1 1 pack_report pack_mapped 1356 1356 As you can see when it completes successfully it gives you a bunch of statistics about what it accomplished In this case you imported 18 objects total for 5 commits into 1 branch Now you can run git log to see your new history git log 2 commit 10bfe7d22ce15ee25b60a824c8982157ca593d41 Author Scott Chacon
204. g If you re on a Windows machine set it to true this converts LF endings into CRLF when you check out code git config global core autocrlf true If you re on a Linux or Mac system that uses LF line endings then you don t want Git to automatically convert them when you check out files however if a file with CRLF endings accidentally gets introduced then you may want Git to fix it You can tell Git to convert CRLF to LF on commit but not the other way around by setting core autocrlf to input git config global core autocrlf input This setup should leave you with CRLF endings in Windows checkouts but LF endings on Mac and Linux systems and in the repository If you re a Windows programmer doing a Windows only project then you can turn off this functionality recording the carriage returns in the repository by setting the config value to false git config global core autocrlf false core whitespace Git comes preset to detect and fix some whitespace issues It can look for four primary whitespace issues two are enabled by default and can be turned off and two aren t enabled by default but can be activated The two that are turned on by default are trailing space which looks for spaces at the end of a line and space before tab which looks for spaces before tabs at the beginning of a line The two that are disabled by default but can be turned on are indent with non tab which looks for lines that begin with eight or m
205. g on what team they re on This is common if you re coming from CVS or Subversion where you ve defined a module or collection of subdirectories and you want to keep this type of workflow A good way to do this in Gitis to make each of the subfolders a separate Git repository and then create superproject Git repositories that contain multiple submodules A benefit of this approach is that you can more specifically define the relationships between the projects with tags and branches in the superprojects Issues with Submodules Using submodules isn t without hiccups however First you must be relatively careful when working in the submodule directory When you run git submodule update it checks out the specific version of the project but not within a branch This is called having a detached head it means the HEAD file points directly to a commit not to a symbolic reference The issue is that you generally don t want to work in a detached head environment because it s easy to lose changes If you do an initial submodule update commit in that submodule directory without creating a branch to work in and then run git submodule update again from the superproject without committing in the meantime Git will overwrite your changes without telling you Technically you won t lose the work but you won t have a branch pointing to it so it will be difficult to retrieve To avoid this issue create a branch when you work in a submodule directory with g
206. g with the iss53 changes you ve made and you don t have to put a lot of effort into reverting those changes before you can work on applying your fix to what is in production All you have to do is switch back to your master branch However before you do that note that if your working directory or staging area has uncommitted changes that conflict with the branch you re checking out Git won t let you switch branches It s best to have a clean working state when you switch branches There are ways to get around this namely stashing and commit amending that I ll cover later For now you ve committed all your changes so you can switch back to your master branch git checkout master Switched to branch master CHAPTER 3 GIT BRANCHING 55 At this point your project working directory is exactly the way it was before you started working on issue 53 and you can concentrate on your hotfix This is an important point to remember Git resets your working directory to look like the snapshot of the commit that the branch you check out points to It adds removes and modifies files automatically to make sure your working copy is what the branch looked like on your last commit to it Next you have a hotfix to make You create a hotfix branch on which to work until it s completed see Figure 3 13 git checkout b hotfix Switched to a new branch hotfix vim index html git commit a m fixed the broken email address hotfi
207. ge 179 181 formatting 181 182 server 183 whitespace 181 182 content addressable filesystem 224 226 contributors in private managed teams 118 123 core autocrlf setting 181 core editor setting 176 core excludesfile setting 178 core pager setting 177 core whitespace setting 182 count objects command 248 custom importer 216 221 customization See configuration D data downloading 243 244 fetching from remote repositories 36 storage 6 7 uploading 242 data model 227 data recovery 245 247 Date keyword expansion 188 datestamp 187 debugging 162 164 binary search 163 164 file annotation 162 163 denyNonFastForwards policy 183 describe command 141 description file 224 dictator and lieutenants workflows 109 diff command 20 23 135 diff external setting 180 diffs viewing 134 152 diff tools 12 179 181 directory git 8 223 224 working 8 55 Distributed Version Control Systems DVCSs 4 distributed workflows 107 109 double dot syntax 148 dumb protocol 240 242 E e mail address changing globally 161 setting 11 e mail workflow hooks 191 errors whitespace 111 letc gitconfig file 11 175 exclude file 224 export data method 218 219 export ignore attribute 189 export subst attribute 189 extDiff tool 180 external merge 179 181 extMerge tool 180 F fast forward only pushes 197 199 fast import tool 216 221 fetch command 36 fetch origin command 65 fetch pack
208. ge date parser edit Homepage http chronic rubyforge org edit Public Clone URL git github com schacon chronic git ir Your Clone URL git github com schacon chronic git if Figure 4 15 Your fork of a project GitHub Summary That s all I ll cover about GitHub but it s important to note how quickly you can do all this You can create an account add a new project and push to it in a matter of minutes If your project is open source you also get a huge community of developers who now have visibility into your project and may well fork it and help contribute to it At the very least this may be a way to get up and running with Git and try it out quickly Summary You have several options to get a remote Git repository up and running so that you can col laborate with others or share your work Running your own server gives you a lot of control and allows you to run the server within your own firewall but such a server generally requires a fair amount of your time to set up and maintain If you place your data on a hosted server it s easy to set up and maintain however you have to be able to keep your code on someone else s servers and some organizations don t allow that It should be fairly straightforward to determine which solution or combination of solu tions is appropriate for you and your organization CHAPTER 5 Distributed Git N that you have a remote Git repository set up as a point for all the developer
209. ged 2 insertions 1 deletions commit fdf4fc3344e67ab068f836878b6c4951e3b15f3d Author Scott Chacon lt schacon gmail com gt Date Fri May 22 18 09 34 2009 0700 230 CHAPTER 9 GIT INTERNALS first commit test txt 1 1 files changed 1 insertions 0 deletions Amazing You ve just done the low level operations to build up a Git history without using any of the front ends This is essentially what Git does when you run the git addand git commit commands t stores blobs for the files that have changed updates the index writes out trees and writes commit objects that reference the top level trees and the commits that came immediately before them These three main Git objects the blob the tree and the commit are initially stored as separate files in your git objects directory Here are all the objects in the example directory now commented with what they store find git objects type f git objects 01 55eb4229851634a0f03eb265b69f5a2d56f341 tree 2 git objects 1a 410efbd13591db07496601ebc7a059dd55cfe9 commit 3 git objects 1f 7a7a472abf3dd9643fd615f6da379c4acb3e3a test txt v2 git objects 3c 4e9cd789488484d89c1073707c3585e41b0e614 tree 3 git objects 83 baae61804e65cc73a7201a7252750c76066a330 test txt v1 git objects ca c0cab538b970a37ea1e769cbbde608743bc96d commit 2 git objects d6 70460b4b4aece5915cafs5c68d12f560a9fe3e4 test content git objects d8 329fc1cc938780ffdd9f94e0d364e0ea74f579 tree 1
210. getting the diff output on the command line Git fires up PAMerge which looks something like Figure 7 1 If you try to merge two branches and subsequently have merge conflicts you can run the command git mergetool it starts PAMerge to let you resolve the conflicts through that GUI tool The nice thing about this wrapper setup is that you can change your diff and merge tools easily For example to change your extDiff and extMerge tools to run the KDiff3 tool instead all you have to do is edit your extMerge file cat usr local bin extMerge bin sh Applications kdiff3 app Contents MacOS kdiff3 Now Git will use the KDiff3 tool for diff viewing and merge conflict resolution Git comes preset to use a number of other merge resolution tools without your having to set up the cmd configuration You can set your merge tool to kdiff3 opendiff tkdiff meld xxdiff emerge vimdiff or gvimdiff If you re not interested in using KDiff3 for diff but rather want to use it just for merge resolution and the kdiff3 command is in your path then you can run git config global merge tool kdiff3 CHAPTER 7 CUSTOMIZING GIT If you run this instead of setting up the extMerge and extDiff files Git will use KDiff3 for merge resolution and the normal Git diff tool for diffs t9 00 diff GBASUP and index ht E E 5 a BE GH 8 Qo ar AAi uS i i H n ending differences Tab spacing 4 Encoding System Refresh all CR
211. ghtweight You can make a lightweight tag by running something like this git update ref refs tags v1 0 cacOcab538b970a37ea1e769cbbde608743bc96d That is all a lightweight tag is a branch that never moves An annotated tag is more complex however If you create an annotated tag Git creates a tag object and then writes a reference to point to it rather than directly to the commit You can see this by creating an annotated tag a specifies that it s an annotated tag git tag a v1 1 1a410efbd13591db07496601ebc7a059dd55cfe9 m test tag Here s the object SHA 1 value it created cat git refs tags v1 1 9585191f37f7b0fb9444f35a9bf50de191beadc2 Now run the cat file command on that SHA 1 value git cat file p 9585191f37f7b0fb9444f35a9bf50de191beadc2 object 1a410efbd13591db07496601ebc7a059dd55cfe9 type commit tag v1 1 tagger Scott Chacon lt schacon gmail com gt Sat May 23 16 48 58 2009 0700 test tag Notice that the object entry points to the commit SHA 1 value that you tagged Also notice that it doesn t need to point to a commit you can tag any Git object In the Git source code for example the maintainer has added their GPG public key as a blob object and then tagged it You can view the public key by running git cat file blob junio gpg pub CHAPTER 9 GIT INTERNALS 235 in the Git source code The Linux kernel also has a non commit pointing tag object the first tag created points to the initial tree of the
212. git fetch origin master refs remotes origin mymaster topic refs remotes origin topic From git github com schacon simplegit rejected master gt origin mymaster non fast forward new branch topic gt origin topic In this case the master branch pull was rejected because it wasn t a fast forward refer ence You can override that by specifying the in front of the refspec You can also specify multiple refspecs for fetching in your configuration file If you want to always fetch the master and experiment branches add two lines remote origin url git github com schacon simplegit progit git fetch refs heads master refs remotes origin master fetch refs heads experiment refs remotes origin experiment You can t use partial globs in the pattern so this would be invalid fetch refs heads qa refs remotes origin qa However you can use namespacing to accomplish something like that If you have a QA team that pushes a series of branches and you want to get the master branch and any of the QA team s branches but nothing else you can use a config section like this remote origin url git github com schacon simplegit progit git fetch refs heads master refs remotes origin master fetch refs heads qa refs remotes origin qa If you have a complex workflow process that has a QA team pushing branches developers pushing branches and integration teams pushing and collaborating on remote branches you
213. gomma COMMA irog snapshot 2daysago Junio C Hamano Merge branch maint gommis oommagit tree snapshot 2daysago Junio C Hamano tests fix export varzval Commis commagi ree snapshot 2days ago Lars Noschinski filter branch d Export GIT DIR earlier comme commadimt tree snapshot 2daysago Jay Soffian disallow providing multiple upstream branches to rebase commis commit irop snapshot 2daysago Michael Spang Skip timestamp differences for diff no index commis commi tree snapshot 2daysago Junio C Hamano git svn fix parsing of timestamp obtained from svn commi commaar tree snapshot 2daysago Marcel M Cary gitweb Fix warnings with override permitted but no Commit commadit treo snapshot 2daysago Gerrit Pape Documentation git push all mirror tags can commis oommadit tree snapshot 2daysago Thomas Rast bash completion only show log merge if merging commi commit tree snapshot Figure 4 1 The GitWeb web based user interface If you want to check out what GitWeb would look like for your project Git comes with a command to fire up a temporary instance if you have a lightweight server on your system like lighttpd or webrick On Linux machines lighttpd is often installed so you may be able to get it to run by typing git instaweb in your project directory If you re running a Mac Leop ard comes preinstalled with Ruby so webrick may be your best bet To start inst
214. group needs it to Git Configuration As you briefly saw in Chapter 1 you can specify Git configuration settings with the git config command One of the first things you did was set up your name and e mail address git config global user name John Doe git config global user email johndoe example com Now you ll learn a few of the more interesting options that you can set in this manner to customize your Git usage You saw some simple Git configuration details in the first chapter but I ll go over them again quickly here Git uses a series of configuration files to determine non default behavior that you may want The first place Git looks for these values is in an etc gitconfig file which contains values for every user on the system and all of their repositories If you pass the option systemto git config it reads and writes from this file specifically The next place Git looks is the gitconfig file which is specific to each user You can make Git read and write to this file by passing the global option Finally Git looks for configuration values in the config file in the Git directory git config of whatever repository you re currently using These values are specific to that single repository Each level overwrites values in the previous level so values in git config trump those in etc sysconfig for instance You can also set these values by manually editing the file and inserting the correct syntax but it s gener
215. he credit required by this Section for the purpose of attribution in the manner set out above and by exercising Your rights under this License You may not implicitly or explicitly assert or imply any connection with sponsorship or endorsement by the Original Author Licensor and or Attribution Parties as appro priate of You or Your use of the Work without the separate express prior written permission of the Original Author Licensor and or Attribution Parties e For the avoidance of doubt i Non waivable Compulsory License Schemes In those jurisdictions in which the right to collect royalties through any statutory or compulsory licensing scheme cannot be waived the Licensor reserves the exclusive right to collect such royalties for any exercise by You of the rights granted under this License ii Waivable Compulsory License Schemes In those jurisdictions in which the right to collect royalties through any statutory or compulsory licensing scheme can be waived the Licensor reserves the exclusive right to collect such royalties for any exercise by You of the rights granted under this License if Your exercise of such rights is for a purpose or use which is otherwise than noncommercial as permitted under Section 4 c and otherwise waives the right to collect royal ties through any statutory or compulsory licensing scheme and iii Voluntary License Schemes The Licensor reserves the right to collect royalties whether individually or in
216. he server to restore it Every checkout is really a full backup of all the data see Figure 1 3 Server Computer Version Database Version 3 Version 2 Version 1 Computer A Computer B Version Database Version Database Figure 1 3 Distributed version control diagram Furthermore many of these systems deal pretty well with having several remote reposi tories they can work with so you can collaborate with different groups of people in different ways simultaneously within the same project This allows you to set up several types of work flows that aren t possible in centralized systems such as hierarchical models CHAPTER 1 GETTING STARTED A Short History of Git As with many great things in life Git began with a bit of creative destruction and fiery contro versy The Linux kernel is an open source software project of fairly large scope For most of the lifetime of the Linux kernel maintenance 1991 2002 changes to the software were passed around as patches and archived files In 2002 the Linux kernel project began using a propri etary DVCS system called BitKeeper In 2005 the relationship between the community that developed the Linux kernel and the commercial company that developed BitKeeper broke down and the tool s free of charge sta tus was revoked This prompted the Linux development community and in particular Linus Torvalds the creator of Linux to develop their own tool based on some of the lessons they le
217. he server you cloned from assuming CHAPTER 2 GIT BASICS 37 the remote has a master branch Running git pull generally fetches data from the server you originally cloned from and automatically tries to merge it into the code you re currently work ing on Pushing to Your Remotes When you have your project at a point that you want to share you have to push it upstream The command for this is simple git push remote name branch name If you want to push your master branch to your origin server again cloning generally sets up both of those names for you automatically then you can run this to push your work back up to the server git push origin master This command works only if you cloned from a server to which you have write access and if nobody has pushed in the meantime If you and someone else clone at the same time and they push upstream and then you push upstream your push will rightly be rejected You ll have to pull down their work first and incorporate it into yours before you ll be allowed to push See Chapter 3 for more detailed information on how to push to remote servers Inspecting a Remote If you want to see more information about a particular remote you can use the git remote show remote name command If you run this command with a particular shortname such as origin you get something like this git remote show origin remote origin URL git github com schacon ticgit git Remote branch merged with g
218. hen all the patches for your topic are applied and committed into your branch you can choose whether and how to integrate them into a longer running branch Checking Out Remote Branches If your contribution came from a Git user who set up their own repository pushed a number of changes into it and then sent you the URL to the repository and the name of the remote branch the changes are in you can add them as a remote and do merges locally For instance if Jessica sends you an e mail saying that she has a great new feature in the ruby client branch of her repository you can test it by adding the remote and checking out that branch locally git remote add jessica git github com jessica myproject git git fetch jessica git checkout b rubyclient jessica ruby client If she e mails you again later with another branch containing another great feature you can fetch and check out because you already have the remote setup This is most useful if you re working with a person consistently If someone only has a single patch to contribute once in a while then accepting it over e mail may be less time consum ing than requiring everyone to run their own server and having to continually add and remove remotes to get a few patches You re also unlikely to want to have hundreds of remotes each for someone who contributes only a patch or two However scripts and hosted services may make this easier it depends largely on how you develop and how y
219. here either everything is applied or nothing is whereas patch can partially apply patchfiles leaving your working directory in a weird state git apply is over all much more paranoid CHAPTER 5 DISTRIBUTED GIT 131 than patch It won t create a commit for you after running it you must stage and commit the changes introduced manually You can also use git apply to see if a patch applies cleanly before you try actually apply ing it you can run git apply check with the patch git apply check 0001 seeing if this helps the gem patch error patch failed ticgit gemspec 1 error ticgit gemspec patch does not apply If there is no output then the patch should apply cleanly This command also exits with a non zero status if the check fails so you can use it in scripts if you want Applying a Patch with am Ifthe contributor is a Git user and was good enough to use the format patch command to generate their patch then your job is easier because the patch contains author information and a commit message for you If you can encourage your contributors to use format patch instead of diff to generate patches for you You should only have to use git apply for legacy patches and things like that To apply a patch generated by format patch you use git am Technically git amis built to read an mbox file which is a simple plain text format for storing one or more e mail mes sages in one text file It looks something like this From 330
220. hey want I ll quickly go over how that is done Setting Up a User Account The first thing you need to do is set up a free user account If you visit the Pricing and Signup page at http github com plans and click the Sign Up button on the Free account see Figure 4 2 you re taken to the signup page github Search Home Pricing and Signup Repositories Blog Login SOCIALCODING Browse Guides Advanced Choose the plan that s right for you Paid plans are billed monthly and can be upgraded downgraded terminated at any time without penalty Open Source Free Gy Unlimited Public Repositories Unlimited Public Collaborators 300 MB Disk Space Figure 4 2 The GitHub plan page 98 CHAPTER 4 GIT ON THE SERVER Here you must choose a username that isn t yet taken in the system and enter an e mail address that will be associated with the account and a password see Figure 4 3 Sign up oc in Username Email Address Password Confirm Password SSH Public Key explain ssh keys Please enter one key only You may add more later This field is not required to sign up You re signing up for the free plan if you have any questions please email support By signing up you agree to the Terms of Service Privacy and Refund policies agree sign me up Figure 4 3 The GitHub user signup form If you have it available this is a g
221. hing new to the master branch What you really want to see are the changes added to the topic branch the work you ll introduce if you merge this branch with master You do that by having Git compare the last commit on your topic branch with the first common ancestor it has with the master branch Technically you can do that by explicitly figuring out the common ancestor and then run ning your diff on it git merge base contrib master 36c7dba2c95e6bbb78dfa822519ecfec6e1ca649 git diff 36c7db CHAPTER 5 DISTRIBUTED GIT 135 However that isn t convenient so Git provides another shorthand for doing the same thing the triple dot syntax In the context of the diff command you can put three periods after another branch to do a diff between the last commit of the branch you re on and its com mon ancestor with another branch git diff master topic This command shows you only the work your topic branch has introduced since its com mon ancestor with master That is a very useful syntax to remember Integrating Contributed Work When all the work in your topic branch is ready to be integrated into a more mainline branch the question is how to do it Furthermore what overall workflow do you want to use to main tain your project You have a number of choices so Ill cover a few of them Merging Workflows One simple workflow merges your work into your master branch In this scenario you have amaster branch that contains basicall
222. hip License Elements means the following high level license attributes as selected by Licensor and indicated in the title of this License Attribution Noncommercial ShareAlike Licensor means the individual individuals entity or entities that offer s the Work under the terms of this License Original Author means in the case of a literary or artistic work the individual individuals entity or entities who created the Work or if no individual or entity can be identified the publisher and in addition i in the case of a performance the actors singers musicians dancers and other persons who act sing deliver declaim play in interpret or otherwise perform literary or artistic works or expres sions of folklore ii in the case of a phonogram the producer being the person or legal entity who first fixes the sounds of a performance or other sounds and iii in the case of broadcasts the organization that transmits the broadcast Work means the literary and or artistic work offered under the terms of this License including without limitation any production in the literary scientific and artistic domain whatever may be the mode or form of its expression including digital form such as a book pamphlet and other writing a lecture address ser mon or other work of the same nature a dramatic or dramatico musical work a choreographic work or entertainment in dumb show a musical composition with or without wor
223. his License constitutes the entire agreement between the parties with respect to the Work licensed here There are no understandings agreements or representa tions with respect to the Work not specified here Licensor shall not be bound by any additional provisions that may appear in any communication from You This License may not be modified without the mutual written agreement of the Licensor and You f The rights granted under and the subject matter referenced in this License were drafted utilizing the terminology of the Berne Convention for the Protection of Literary and Artistic Works as amended on September 28 1979 the Rome Con vention of 1961 the WIPO Copyright Treaty of 1996 the WIPO Performances and Phonograms Treaty of 1996 and the Universal Copyright Convention as revised on July 24 1971 These rights and subject matter take effect in the relevant juris diction in which the License terms are sought to be enforced according to the corresponding provisions of the implementation of those treaty provisions in the applicable national law If the standard suite of rights granted under applicable copyright law includes additional rights not granted under this License such addi tional rights are deemed to be included in the License this License is not intended to restrict the license of any rights under applicable law Creative Commons Notice Creative Commons is not a party to this License and makes no warranty whatsoever in co
224. hoose from bold dim ul blink and reverse See the git config manpage for all the subsettings you can configure if you want to do that External Merge and Diff Tools Although Git has an internal implementation of diff which is what you ve been using you can set up an external tool instead You can also set up a graphical merge conflict resolution tool instead of having to resolve conflicts manually I ll demonstrate setting up the Perforce Visual Merge Tool PAMerge to do your diffs and merge resolutions because it s a nice graphi cal tool and it s free If you want to try this PAMerge works on all major platforms so you should be able to do so I ll use path names in the examples that work on Mac and Linux systems for Windows you ll have to change usr local bin to an executable path in your environment You can download PAMerge here http www perforce com perforce downloads component html To begin you ll set up external wrapper scripts to run your commands I ll use the Mac path for the executable in other systems it will be where your p4merge binary is installed Set up a merge wrapper script named extMerge that calls your binary with all the arguments pro vided cat usr local bin extMerge it bin sh Applications p4merge app Contents MacOS p4merge The diff wrapper checks to make sure seven arguments are provided and passes two of them to your merge script By default Git passes the following arguments to the
225. hot it s the history that is different Rebasing replays changes from one line of work onto another in the order they were introduced whereas merging takes the endpoints and merges them together More Interesting Rebases You can also have your rebase replay on something other than the rebase branch Take a history like Figure 3 31 for example You branched a topic branch server to add some server side functionality to your project and made a commit Then you branched off that to make the client side changes client and committed a few times Finally you went back to your server branch and did a few more commits master 6 amp t server 8 C a iren client Figure 3 31 A history with a topic branch off another topic branch Suppose you decide that you want to merge your client side changes into your mainline for a release but you want to hold off on the server side changes until it s tested further You can take the changes on client that aren t on server C8 and C9 and replay them on your master branch by using the onto option of git rebase git rebase onto master server client CHAPTER 3 GIT BRANCHING 73 This basically says Check out the client branch figure out the patches from the com mon ancestor of the client and server branches and then replay them onto master It s a bit complex but the result shown in Figure 3 32 is pretty cool Figure 3 32 Rebasing a topi
226. iends and family When you rebase stuff you re abandoning existing commits and creating new ones that are similar but different If you push commits somewhere and others pull them down and base work on them and then you rewrite those commits with git rebase and push them up again your collaborators will have to re merge their work and things will get messy when you try to pull their work back into yours CHAPTER 3 GIT BRANCHING 75 Let s look at an example of how rebasing work that you ve made public can cause prob lems Suppose you clone from a central server and then do some work off that Your commit history looks like Figure 3 36 git team1 ourcompany com e L1 My Computer E G A Figure 3 36 Clone a repository and base some work on it Now someone else does more work that includes a merge and pushes that work to the central server You fetch them and merge the new remote branch into your work making your history look something like Figure 3 37 git team1 ourcompany com e My Computer teamone master master Figure 3 37 Fetch more commits and merge them into your work CHAPTER 3 GIT BRANCHING Next the person who pushed the merged work decides to go back and rebase their work instead they do agit push force to overwrite the history on the server You then fetch from that server bringing down the new commits see Figure 3 38 git team1 ourcompany com
227. ient Git does this if you have too many loose objects around if you run the git gc command manually or if you push to a remote server To see what happens you can manually ask Git to pack up the objects by call ingthegit gc command git gc Counting objects 17 done Delta compression using 2 threads Compressing objects 100 13 13 done Writing objects 100 17 17 done Total 17 delta 1 reused 10 delta 0 If you look in your objects directory you ll find that most of your objects are gone and a new pair of files has appeared find git objects type f git objects 71 08f7ecb345ee9d0084193f147cdad4d2998293 git objects d6 70460b4b4aece5915caf5c68d12f560a9fe3e4 git objects info packs git objects pack pack 7a16e4488ae40c7d2bc56ea2bd43e25212a66c45 idx git objects pack pack 7a16e4488ae40c7d2bc56ea2bd43e25212a66c45 pack The objects that remain are the blobs that aren t pointed to by any commit in this case the what is up doc example and the test content example blobs you created ear lier Because you never added them to any commits they re considered dangling and aren t packed up in your new packfile The other files are your new packfile and an index The packfile is a single file containing the contents of all the objects that were removed from your filesystem The index is a file that contains offsets into that packfile so you can quickly seek to a specific object What is coolis that although the obje
228. ild system In such cases you can create a file named gitignore listing patterns to match them Here is an example gitignore file cat gitignore oa kn The first line tells Git to ignore any files ending in o or a object and archive files that may be the product of building your code The second line tells Git to ignore all files that end with a tilde which is used by many text editors such as Emacs to mark temporary files You may also include a log tmp or pid directory automatically generated documentation and so on Setting up a gitignore file before you get going is generally a good idea so you don t accidentally commit files that you really don t want in your Git repository The rules for the patterns you can put in the gitignore file are as follows Blank lines or lines starting with are ignored e Standard glob patterns work Youcan end patterns with a forward slash to specify a directory Youcan negate a pattern by starting it with an exclamation point Glob patterns are like simplified regular expressions that shells use An asterisk matches zero or more characters abc matches any character inside the brackets in this case a b or c a question mark matches a single character and brackets enclosing characters separated by a hyphen 0 9 matches any character between them in this case 0 through 9 Here is another example gitignore file a comment this is ignored
229. imple branch and checkout commands master 87ab2 iH IHH Figure 3 9 The branch histories have diverged Because a branch in Git is in actuality a simple file that contains the 40 character SHA 1 checksum of the commit it points to branches are cheap to create and destroy Creating a new branch is as quick and simple as writing 41 bytes to a file 40 characters and a newline This is in sharp contrast to the way most VCS tools branch which involves copying all of the project s files into a second directory This can take several seconds or even minutes depending on the size of the project whereas in Git the process is always instantaneous Also because you re recording the parents when you commit finding a proper merge base for merging is automatically done for you and is generally very easy These features help encour age developers to create and use branches often Let s see why you should do so CHAPTER 3 GIT BRANCHING 53 Basic Branching and Merging Let s go through a simple example of branching and merging with a workflow that you might use in the real world You ll follow these steps 1 Do work on a web site 2 Create a branch for a new story you re working on 3 Do some work in that branch At this stage you ll receive a call that another issue is critical and you need a hotfix You ll do the following 1 Revert back to your production branch 2 Create a branch to add the hotfix 3 After i
230. import of the source code Remotes The third type of reference that you ll see is a remote reference If you add a remote and push to it Git stores the value you last pushed to that remote for each branch in the refs remotes directory For instance you can add a remote called origin and push your master branch to it git remote add origin git github com schacon simplegit progit git git push origin master Counting objects 11 done Compressing objects 100 5 5 done Writing objects 100 7 7 716 bytes done Total 7 delta 2 reused 4 delta 1 To git github com schacon simplegit progit git allbefO ca82a6d master gt master Then you can see what the master branch on the origin remote was the last time you communicated with the server by checking the refs remotes origin master file cat git refs remotes origin master ca82a6dff817ec66f44342007202690a93763949 Remote references differ from branches refs heads references mainly in that they can t be checked out Git moves them around as bookmarks to the last known state of where those branches were on those servers Packfiles Let s go back to the objects database for your test Git repository At this point you have 11 objects 4 blobs 3 trees 3 commits and 1 tag find git objects type f git objects 01 55eb4229851634a0f03eb265b69f5a2d56f341 tree 2 git objects 1a 410efbd13591db07496601ebc7a059dd55cfe9 commit 3 git objects 1f 7a7a472abf3dd9643fd615f
231. in Your strategy will be to go through the snapshots one at a time and create commits with the contents of each directory linking each commit back to the previous one As you did in the An Example Git Enforced Policy section of Chapter 7 you ll write this in Ruby because it s what I generally work with and it tends to be easy to read You can write this example pretty easily in anything you re familiar with it just needs to print the appropri ate information to stdout To begin you ll change into the target directory and identify every subdirectory each of which is a snapshot that you want to import as a commit You ll change into each subdirectory and print the commands necessary to export it Your basic main loop looks like this CHAPTER 8 GIT AND OTHER SYSTEMS last_mark nil loop through the directories Dir chdir ARGV 0 do Dir glob each do dir next if File file dir move into the target directory Dir chdir dir do last_mark print_export dir last_mark end end end You run print_export inside each directory which takes the manifest and mark of the previous snapshot and returns the manifest and mark of this one that way you can link them properly Mark is the fast import term for an identifier you give to a commit as you create commits you give each one a mark that you can use to link to it from other commits So the first thing to do in your print_export method is generate a mark from the directory name
232. ing custom 216 221 from Perforce 214 216 from Subversion 213 214 indent program 187 index file 8 224 index filter option 249 index option 155 interactive option 150 info directory 224 installation Git 9 11 integration manager workflows 108 interactive staging 150 153 ioption 150 K KDiff3 tool 180 keydir directory 93 94 key value data store 224 keyword expansion 186 189 L large merging workflows 137 139 Leopard 90 lieutenants 109 lighttpd server 90 lightweight tags 39 234 Linux installing Git on 10 Linux kernel 5 109 144 Local protocol 80 81 local repository adding to existing project 80 log command 26 32 158 log g command 146 log information 145 146 log output formatting 28 30 limiting 30 31 long running branches 63 loose object format 236 maintenance 244 245 manual page manpage 13 master branch 17 56 62 merge command 55 57 merge commits 57 merged option 61 merges merging basic 53 57 branches 70 conflicts 58 60 subtree 171 172 strategies 171 190 three way 133 tools 60 mergetool command 59 180 mergetool cmd setting 180 merge tool setting 180 mergetool trustExitCode setting 180 migration to Git 212 221 modified files unmodifying 34 modified state 8 multiple repository workflows 109 mv command 25 26 N network protocols 79 83 Git 81 82 95 96 HTTP S 82 83 240 242 Local 80 81 SSH 81 no commit option 126
233. ing 153 156 static web server 88 stat option 28 status checking of files 17 18 status command 17 20 165 subdirectories 161 submodule add command 165 submodule init command 167 submodules 165 171 cloning project with 167 169 getting started with 165 166 issues with 169 171 submodule update command 167 169 subtrees merging 171 172 Subversion annotation 211 branching 209 210 commands 210 212 committing back to 206 207 Git and 203 212 importing from on GitHub 101 importing repository into Git repository 205 migrating to Git from 213 214 pulling in new changes 207 208 server information 211 style history 210 superprojects 169 svn blame FILE command 211 svn info command 211 SVN style history 211 svn tool 203 212 branching issues 208 209 clone command 204 205 dcommit command 206 208 fetch command 208 getting started 204 206 pulling in new changes 207 208 rebase command 207 208 setting up 204 summary 212 svnsync tool 204 symlink creating 92 T tag command 39 41 tags tagging 38 43 234 235 adding later 42 annotated 39 141 creating 39 41 lightweight 39 listing 39 sharing 43 signed 40 140 141 verifying 41 tail command 248 test error sh 164 text editor setting default 12 three way merges 133 tilde 20 147 tools See Git tools topic branches 63 64 integrating 139 140 managing parallel 137 working in 130 tracked files 16 tracking branches
234. ion control system The JGit library can often be found in Java based products that interact with Git including Git plug ins for the popular Eclipse and NetBeans IDEs the Hudson CI server Apache Maven and Gerrit Code Review a peer code review sys tem specially designed for Git Today he continues to develop and maintain JGit EGit the Eclipse plug in based on top of it and Gerrit Code Review Acknowledgments F I would like to thank the entire Git development community for giving us such a great tool I dislike working in C and so have contributed little actual code to the Git project opting instead to try to teach document and evangelize it which I tend to be a lot better at However without the guys that wrote and maintain Git I would still be living in the sad and hopeless version controlled world that is Subversion I would also very much like to thank Shawn Pearce who aside from being one of the more prolific developers on the Git project is also the technical editor for this book Shawn has saved me from making countless horrible technical mistakes in this book and has done so on numer ous other occasions as well I always enjoy working with him I tend to give my best guess at something and then he teaches me what the right answer is I have learned a ton from him which I often get to teach to hundreds of others who then give me credit I want to thank my good friend Nick Hengeveld who has contributed a lot of work to Gi
235. irst section of this chapter will cover the available protocols and the pros and cons of each The next sections will explain some typical setups using those proto cols and how to get your server running with them Last I ll go over a few hosted options if you don t mind hosting your code on someone else s server and don t want to go through the hassle of setting up and maintaining your own server If you have no interest in running your own server you can skip to the last section of the chapter to see some options for setting up a hosted account and then move on to the next chapter where I discuss the various ins and outs of working in a distributed source control environment A remote repository is generally a bare repository a Git repository that has no working directory Because the repository is only used as a collaboration point there is no reason to have a snapshot checked out on disk it s just the Git data In the simplest terms a bare reposi tory is the contents of your project s git directory and nothing else The Protocols Git can use four major network protocols to transfer data Local Secure Shell SSH Git and HTTP Here I ll discuss what they are and in what basic circumstances you would want or not want to use them It s important to note that with the exception of the HTTP protocols all of these require Git to be installed and working on the server 79 80 CHAPTER 4 GIT ON THE SERVER Local Protocol The
236. is command to pull in changes from the Subversion server even if you re not ready to commit yourself You can run git svn fetch to grab the new data but git svn rebase does the fetch and then updates your local commits git svn rebase M generate descriptor proto sh 182 bd16df9173e424c6f52c337ab6efa7f7643282f1 trunk First rewinding head to replay your work on top of it Fast forwarded master to refs remotes trunk Runninggit svn rebase every once in a while makes sure your code is always up to date You need to be sure your working directory is clean when you run this though If you have local changes you must either stash your work or temporarily commit it before running git svn rebase otherwise the command will stop if it sees that the rebase will result in a merge conflict Git Branching Issues When you ve become comfortable with a Git workflow you ll likely create topic branches do work on them and then merge them in If you re pushing to a Subversion server via git svn you may want to rebase your work onto a single branch each time instead of merging branches together The reason to prefer rebasing is that Subversion has a linear history and doesn t deal with merges like Git does so git svn follows only the first parent when converting the snap shots into Subversion commits CHAPTER 8 GIT AND OTHER SYSTEMS 209 Suppose your history looks like the following you created an experiment branch did two commits and then
237. is often referred to as the dumb protocol because it requires no Git specific code on the server side during the transport process The fetch process is a series of GET requests where the client can assume the layout of the Git repository on the server Let s follow the http fetch process for the simplegit library git clone http github com schacon simplegit progit git The first thing this command does is pull down the info refs file This file is written by the update server info command which is why you need to enable that as a post receive hook in order for the HTTP transport to work properly gt GET info refs ca82a6dff817ec66f44342007202690a93763949 refs heads master Now you have a list of the remote references and SHAs Next you look for what the HEAD reference is so you know what to check out when you re finished GET HEAD ref refs heads master You need to check out the master branch when you ve completed the process CHAPTER 9 GIT INTERNALS 241 At this point you re ready to start the walking process Because your starting point is the ca82a6 commit object you saw in the info refs file you start by fetching that gt GET objects ca 82a6dff817ec66F44342007202690a93763949 179 bytes of binary data You get an object back that object is in loose format on the server and you fetched it over a static HTTP GET request You can zlib uncompress it strip off the header and look at the commit content git
238. it checkout b work or something equivalent When you do the submodule update a second time it will still revert your work but at least you have a pointer to get back to Switching branches with submodules in them can also be tricky If you create a new branch add a submodule there and then switch back to a branch without that submodule you still have the submodule directory as an untracked directory git checkout b rack Switched to a new branch rack git submodule add git github com schacon rack git rack Initialized empty Git repository in opt myproj rack git Receiving objects 100 3184 3184 677 42 KiB 34 KiB s done Resolving deltas 100 1952 1952 done git commit am added rack submodule 170 CHAPTER 6 GIT TOOLS rack cc49a69 added rack submodule 2 files changed 4 insertions 0 deletions create mode 100644 gitmodules create mode 160000 rack git checkout master Switched to branch master git status On branch master Untracked files use git add lt file gt to include in what will be committed rack You have to either move it out of the way or remove it in which case you have to clone it again when you switch back and you may lose local changes or branches that you didn t push up The last main caveat that many people run into involves switching from subdirectories to submodules If you ve been tracking files in your project and you want to move them out into a
239. it and Other Systems The world isn t perfect Usually you can t immediately switch every project you come in contact with to Git Sometimes you re stuck on a project using another VCS and many times that system is Subversion You ll spend the first part of this chapter learning about git svn the bidirectional Subversion gateway tool in Git At some point you may want to convert your existing project to Git The second part of this chapter covers how to migrate your project into Git first from Subversion then from Perforce and finally via a custom import script for a nonstandard importing case Git and Subversion Currently the majority of open source development projects and a large number of corporate projects use Subversion to manage their source code It s the most popular open source VCS and has been around for nearly a decade It s also very similar in many ways to CVS which was the big boy of the source control world before that One of Git s great features is a bidirectional bridge to Subversion called git svn This tool allows you to use Git as a valid client to a Subversion server so you can use all the local features of Git and then push to a Subversion server as if you were using Subversion locally This means you can do local branching and merging use the staging area use rebasing and cherry picking and so on while your collaborators continue to work in their dark and ancient ways It s a good way to sneak Git int
240. it applies both that change and the change directly before it and makes you merge the commit messages together So if you want to make a single commit from these three commits you make the script look like this pick f7f3f6d changed my name a bit squash 310154e updated README formatting and added blame squash a5f4a0d added cat file When you save and exit the editor Git applies all three changes and then puts you back into the editor to merge the three commit messages This is a combination of 3 commits The first commit s message is changed my name a bit This is the 2nd commit message updated README formatting and added blame This is the 3rd commit message added cat file 160 CHAPTER 6 GIT TOOLS When you save that you have a single commit that introduces the changes of all three previous commits Splitting a Commit Splitting a commit undoes a commit and then partially stages and commits as many times as commits you want to end up with For example suppose you want to split the middle com mit of your three commits Instead of updated README formatting and added blame you want to split it into two commits updated README formatting for the first and added blame for the second You can do that in the rebase i script by changing the instruction on the commit you want to split to edit pick f7f3f6d changed my name a bit edit 310154e updated README formatting and added blame pick a5f4a0d added cat file Then
241. it pull while on branch master master Tracked remote branches master ticgit Itlists the URL for the remote repository as well as the tracking branch information The command helpfully tells you that if you re on the master branch and you run git pull it will automatically merge in the master branch on the remote after it fetches all the remote refer ences It also lists all the remote references it has pulled down That is a simple example you re likely to encounter When you re using Git more heavily however you may see much more information from git remote show git remote show origin remote origin URL git github com defunkt github git Remote branch merged with git pull while on branch issues issues Remote branch merged with git pull while on branch master master New remote branches next fetch will store in remotes origin caching 38 CHAPTER 2 GIT BASICS Stale tracking branches use git remote prune libwalker walker2 Tracked remote branches acl apiv2 dashboard2 issues master postgres Local branch pushed with git push master master This command shows which branch is automatically pushed when you run git push on certain branches It also shows you which remote branches on the server you don t yet have which remote branches you have that have been removed from the server and multiple branches that are automatically merged when you run git pull Removing and Renaming Remotes If you want to rename
242. it reads the root tree of one branch into your current index and working directory You just switched back to your master branch and you pull the rack branch into the rack subdirectory of your master branch main project git read tree prefix rack u rack branch When you commit it looks like you have all the Rack files under that subdirectory as though you copied them in from a tarball What gets interesting is that you can fairly easily merge changes from one of the branches to the other So if the Rack project updates you can pull in upstream changes by switching to that branch and pulling git checkout rack branch git pull Then you can merge those changes back into your master branch You can use git merge s subtree and it will work fine but Git will also merge the histories together which you probably don t want To pull in the changes and prepopulate the commit message use the squash and no commit options as well as the s subtree strategy option git checkout master git merge squash s subtree no commit rack branch Squash commit not updating HEAD Automatic merge went well stopped before committing as requested All the changes from your Rack project are merged in and ready to be committed locally You can also do the opposite make changes in the rack subdirectory of your master branch and then merge them into your rack branch branch later to submit them to the maintainers or push them upstream To
243. its a day or possibly less for somewhat dormant projects For really large companies or projects the number of developers could be in the thousands with dozens or even hundreds of patches coming in each day This is important because with more and more developers you run into more issues with making sure your code applies cleanly or can be easily merged Changes you submit may be rendered obsolete or severely broken by work that is merged in while you were working or while your changes were waiting to be approved or applied How can you keep your code consistently up to date and your patches valid The next variable is the workflow in use for the project Is it centralized with each devel oper having equal write access to the main codeline Does the project have a maintainer or integration manager who checks all the patches Are all the patches peer reviewed and approved Are you involved in that process Is a lieutenant system in place and do you have to submit your work to them first CHAPTER 5 DISTRIBUTED GIT 111 The next issue is your commit access The workflow required in order to contribute to a project is much different if you have write access to the project than if you don t If you don t have write access how does the project prefer to accept contributed work Does it even have a policy How much work are you contributing at a time How often do you contribute All these questions can affect how you contribute effectively to a pro
244. iving objects 100 3181 3181 675 42 KiB 173 KiB s done Resolving deltas 100 1951 1951 done Submodule path rack checked out 08d709f78b8c5b0fbeb7821e37fa53e69afcf433 Now your rack subdirectory is at the exact state it was in when you committed earlier If another developer makes changes to the rack code and commits and you pull that reference down and merge it in you get something a bit odd git merge origin master Updating 0550271 85a3eee 168 CHAPTER 6 GIT TOOLS Fast forward rack 2 1 files changed 1 insertions 1 deletions master git status On branch master Changed but not updated use git add lt file gt to update what will be committed use git checkout file to discard changes in working directory modified rack You merged in what is basically a change to the pointer for your submodule but it doesn t update the code in the submodule directory so it looks like you have a dirty state in your working directory git diff diff git a rack b rack index 6c5e70b 08d709f 160000 a rack b rack 1 1 QQ Subproject commit 6c5e70b984a60b3cecd395edd5b48a7575bf58e0 Subproject commit 08d709f78b8c5b0fbeb7821e37fa53e69afcf433 This is the case because the pointer you have for the submodule isn t what is actually in the submodule directory To fix this you must run git submodule update again git submodule update remote Counting obje
245. ject and what work flows are preferred or available to you I ll cover aspects of each of these in a series of use cases moving from simple to more complex you should be able to construct the specific workflows you need in practice from these examples Commit Guidelines Before you start looking at the specific use cases here s a quick note about commit mes sages Having a good guideline for creating commits and sticking to it makes working with Git and collaborating with others a lot easier The Git project provides a document that lays out a number of good tips for creating commits from which to submit patches you can read it in the Git source code in the Documentation SubmittingPatches file First you don t want to submit any whitespace errors Git provides an easy way to check for this before you commit run git diff check which identifies possible whitespace errors and lists them for you Here is an example where I ve replaced a red terminal color with Xs git diff check lib simplegit rb 5 trailing whitespace Qgit dir File expand path git dir XX lib simplegit rb 7 trailing whitespace XXXXXXXXXXX lib simplegit rb 26 trailing whitespace def command git cmd XXXX If you run that command before committing you can tell if you re about to commit whitespace issues that may annoy other developers Next try to make each commit a logically separate changeset If you can try to make your changes digestible
246. jects 100 3 3 done Writing objects 100 3 3 323 bytes done Total 3 delta 1 reused 0 delta 0 Unpacking objects 100 3 3 done Enforcing Policies refs heads master 8338c5 c5b616 POLICY Cannot push a non fast forward reference error hooks update exited with error code 1 error hook declined to update refs heads master To git gitserver project git remote rejected master gt master hook declined error failed to push some refs to git gitserver project git There are a couple of interesting things here First you see this where the hook starts run ning Enforcing Policies xefs heads master fb8c72 c56860 Notice that you printed that out to stdout at the very beginning of your update script It s important to note that anything your script prints to stdout will be transferred to the client The next thing you ll notice is the error message POLICY Cannot push a non fast forward reference error hooks update exited with error code 1 error hook declined to update refs heads master The first line was printed out by you the other two were Git telling you that the update script exited non zero and that is what is declining your push Lastly you have this To git gitserver project git remote rejected master master hook declined error failed to push some refs to git gitserver project git You ll see a remote rejected message for each reference that your hook declined and it tel
247. k and sorting on the third field in the output which is file size You can also pipe it through the tail command because you re only interested in the last few largest files git verify pack v git objects pack pack 3f8cO bb idx sort k 3 n tail 3 e3f09415226292e358806b17daf78246c27c007b blob 1486 734 4667 05408d195263d853f09dca71d55116663690c27c blob 12908 3478 1189 7a9eb2fba2b1811321254ac360970fc169ba2330 blob 2056716 2056872 5401 The big object is at the bottom 2MB To find out what file it is you ll use the rev list command which you used briefly in Chapter 7 If you pass objects to rev list it lists all the commit SHAs and also the blob SHAs with the file paths associated with them You can use this to find your blob s name CHAPTER 9 GIT INTERNALS 249 git rev list objects all grep 7a9eb2fb 7a9eb2fba2b1811321254ac360970fc169ba2330 git tbz2 Now you need to remove this file from all trees in your past You can easily see what commits modified this file git log pretty oneline git tbz2 da3f30d019005479c99eb4c3406225613985a1db oops removed large tarball 6df764092f3e7c8f5f94cbe08ee5cf42e92a0289 added git tarball You must rewrite all the commits downstream from 6df76 to fully remove this file from your Git history To do so you use filter branch which you used in Chapter 6 git filter branch index filter V git rm cached ignore unmatch git tbz2 6df7640 Rewrite 6df764092f3e7c8f5f94
248. k project as a remote reference in your own project and then check it out into its own branch git remote add rack remote git github com schacon rack git git fetch rack remote warning no common commits remote Counting objects 3184 done remote Compressing objects 100 1465 1465 done remote Total 3184 delta 1952 reused 2770 delta 1675 Receiving objects 100 3184 3184 677 42 KiB 4 KiB s done Resolving deltas 100 1952 1952 done From git github com schacon rack new branch build gt rack_remote build new branch master gt rack_remote master new branch rack 0 4 gt rack remote rack 0 4 new branch rack 0 9 gt rack remote rack 0 9 git checkout b rack branch rack remote master Branch rack branch set up to track remote branch refs remotes rack remote master Switched to a new branch rack branch Now you have the root of the Rack project in your rack branch branch and your own proj ect in the master branch If you check out one and then the other you can see that they have different project roots 1s AUTHORS KNOWN ISSUES Rakefile contrib lib 172 CHAPTER 6 GIT TOOLS COPYING README bin example test git checkout master Switched to branch master 1s README You want to pull the Rack project into your master project as a subdirectory You can do that in Git with git read tree You ll learn more about read tree and its friends in Chapter 9 but for now know that
249. l Git objects are stored the same way just with different types instead of the string blob the header will begin with commit or tree Also although the blob content can be nearly anything the commit and tree content are very specifically formatted Git References You can run something like git log 1a410e to look through your whole history but you still have to remember that 1a410e is the last commit in order to walk that history to find all those objects You need a file in which you can store the SHA 1 value under a simple name so you can use that pointer rather than the raw SHA 1 value In Git these are called references or refs you can find the files that contain the SHA 1 values in the git refs directory In the current project this directory contains no files but it does contain a simple structure find git refs git refs git refs heads git refs tags find git refs type f To create a new reference that will help you remember where your latest commit is you can technically do something as simple as this echo 1a410efbd13591db07496601ebc7a059dd55cfe9 git refs heads master Now you can use the head reference you just created instead of the SHA 1 value in your Git commands git log pretty oneline master 1a410efbd13591db07496601ebc7a059dd55cfe9 third commit cac0cab538b970a37ea1e769cbbde608743bc96d second commit fdf4fc3344e67ab068f836878b6c4951e3b15f3d first commit You aren t encouraged to directl
250. ld run those files through the word filter which is defined as the strings pro gram This effectively makes nice text based versions of your Word files before attempting to diff them Here s an example I put Chapter 1 of this book into Git added some text to a paragraph and saved the document Then Iran git diff to see what changed git diff diff git a chapter1 doc b chapter1 doc index c1c8a0a b93c9e4 100644 a chapter1 doc b chapteri doc 8 7 48 8 re going to cover Version Control Systems VCS and Git basics re going to cover how to get it and set it up for the first time if you don t already have it on your system In Chapter Two we will go over basic Git usage how to use Git for the 80 s going on modify stuff and contribute changes If the book spontaneously s going on modify stuff and contribute changes If the book spontaneously Let s see if this works Chapter Three is about the branching model in Git often described as Git 186 CHAPTER 7 CUSTOMIZING GIT Git successfully and succinctly tells me that I added the string Let s see if this works which is correct It s not perfect it adds a bunch of random stuff at the end but it certainly works If you can find or write a Word to plain text converter that works well enough that solution will likely be incredibly effective However strings is available on most Mac and Linux systems so it may be a good first try to do this with many
251. legit progit git fetch refs heads refs remotes origin The format of the refspec is an optional followed by lt src gt lt dst gt where lt src gt is the pattern for references on the remote side and lt dst gt is where those references will be written locally The tells Git to update the reference even if it isn t a fast forward In the default case that is automatically written by a git remote add command Git fetches all the references under refs heads on the server and writes them to refs remotes origin locally So if there is amaster branch on the server you can access the log of that branch locally via git log origin master git log remotes origin master git log refs remotes origin master They re all equivalent because Git expands each of them to refs remotes origin master If you want Git instead to pull down only the master branch each time and not every other branch on the remote server you can change the fetch line to fetch refs heads master refs remotes origin master CHAPTER 9 GIT INTERNALS 239 This is just the default refspec for git fetch for that remote If you want to do something one time you can specify the refspec on the command line too To pull the master branch on the remote down to origin mymaster locally you can run git fetch origin master refs remotes origin mymaster You can also specify multiple refspecs On the command line you can pull down several branches like so
252. letions This looks a bit different than the hotfix merge you did earlier In this case your develop ment history has diverged from some older point Because the commit on the branch you re on isn t a direct ancestor of the branch you re merging in Git has to do some work In this case Git does a simple three way merge using the two snapshots pointed to by the branch tips and the common ancestor of the two Figure 3 16 highlights the three snapshots that Git uses to do its merge in this case Instead of just moving the branch pointer forward Git creates a new snapshot that results from this three way merge and automatically creates a new commit that points to it see Figure 3 17 This is referred to as a merge commit and is special in that it has more than one parent It s worth pointing out that Git determines the best common ancestor to use for its merge base this is different than CVS or Subversion before version 1 5 where the developer doing the merge has to figure out the best merge base for themselves This makes merging a heck of a lot easier in Git than in these other systems Now that your work is merged in you have no further need for the iss53 branch You can delete it and then manually close the ticket in your ticket tracking system git branch d iss53 58 CHAPTER 3 GIT BRANCHING Snapshot to Merge Into OOO B A Snapshot to Merge In Figure 3 16 Git automatically identifies the best common ancestor
253. ll it back out again You can also do this with con tent in files For example you can do some simple version control on a file First create a new file and save its contents in your database echo version 1 test txt git hash object w test txt 83baae61804e65cc73a7201a7252750c76066a30 Then write some new content to the file and save it again echo version 2 test txt git hash object w test txt 1f7a7a472abf3dd9643fd615f6da379c4acb3e3a Your database contains the two new versions of the file as well as the first content you stored there find git objects type f git objects 1f 7a7a472abf3dd9643fd615f6da379c4acb3e3a git objects 83 baae61804e65cc73a7201a7252750c76066a30 git objects d6 70460b4b4aece5915caf5c68d12f560a9fe3e4 Now you can revert the file back to the first version git cat file p 83baae61804e65cc73a7201a7252750c76066a30 gt test txt cat test txt version 1 226 CHAPTER 9 GIT INTERNALS or the second version git cat file p 1f7a7a472abf3dd9643fd615f6da379c4acb3e3a gt test txt cat test txt version 2 But remembering the SHA 1 key for each version of your file isn t practical plus you aren t storing the filename in your system just the content This object type is called a blob You can have Git tell you the object type of any object in Git given its SHA 1 key with cat file t git cat file t 1f7a7a472abf3dd9643fd615f6da379c4acb3e3a blob Tree Objects The next type
254. ls you that it was declined specifically because of a hook failure Furthermore if the ref marker isn t there in any of your commits you ll see the error mes sage you re printing out for that POLICY Your message is not formatted correctly Or if someone tries to edit a file they don t have access to and push a commit contain ing it they will see something similar For instance if a documentation author tries to push a commit modifying something in the lib directory they see POLICY You do not have access to push to lib test rb CHAPTER 7 CUSTOMIZING GIT 199 That s all From now on as long as that update script is there and executable your reposi tory will never be rewound and will never have a commit message without your pattern in it and your users will be sandboxed Client Side Hooks The downside to this approach is the whining that will inevitably result when your users com mit pushes are rejected Having their carefully crafted work rejected at the last minute can be extremely frustrating and confusing and furthermore they will have to edit their history to correct it which isn t always for the faint of heart The answer to this dilemma is to provide some client side hooks that users can use to notify them when they re doing something that the server is likely to reject That way they can correct any problems before committing and before those issues become more difficult to fix Because hooks aren t transferred with
255. lso incredibly error prone It s easy to forget which directory you re in and accidentally write to the wrong file or copy over files when you don t mean to To deal with this issue programmers long ago developed local VCSs that had a simple database that kept all the changes to files under revision control see Figure 1 1 One of the more popular VCS tools was a system called res which is still distributed with many computers today Even the popular Mac OS X operating system includes the rcs com mand when you install the Developer Tools This tool basically works by keeping patch sets that is the differences between files from one change to another in a special format on disk it can then re create what any file looked like at any point in time by adding up all the patches Local Computer Version Database Figure 1 1 Local version control diagram CHAPTER 1 GETTING STARTED Centralized Version Control Systems The next major issue that people encounter is that they need to collaborate with developers on other systems To deal with this problem Centralized Version Control Systems CVCSs were developed These systems such as CVS Subversion and Perforce have a single server that contains all the versioned files and a number of clients that check out files from that central place For many years this has been the standard for version control see Figure 1 2 This setup offers many advantages especially over local VCSs For
256. m English to Spanish or a modification could indicate The original work has been modified c to Distribute and Publicly Perform the Work including as incorporated in Collec tions and d to Distribute and Publicly Perform Adaptations The above rights may be exercised in all media and formats whether now known or here after devised The above rights include the right to make such modifications as are technically necessary to exercise the rights in other media and formats Subject to Section 8 f all rights not expressly granted by Licensor are hereby reserved including but not limited to the rights described in Section 4 e 254 APPENDIX CREATIVE COMMONS LEGAL CODE 4 Restrictions The license granted in Section 3 above is expressly made subject to and limited by the following restrictions a You may Distribute or Publicly Perform the Work only under the terms of this License You must include a copy of or the Uniform Resource Identifier URI for this License with every copy of the Work You Distribute or Publicly Perform You may not offer or impose any terms on the Work that restrict the terms of this License or the ability of the recipient of the Work to exercise the rights granted to that recipient under the terms of the License You may not sublicense the Work You must keep intact all notices that refer to this License and to the disclaimer of warranties with every copy of the Work You Distribute or Publicly Perform
257. made by recursive lib simplegit rb 4 1 files changed 4 insertions O deletions There is a bit of a problem she needs to push the merged work in her featureB branch to the featureBee branch on the server She can do so by specifying the local branch followed by a colon followed by the remote branch to the git push command git push origin featureB featureBee To jessica githost simplegit git fbagaf8 cd685d1 featureB gt featureBee CHAPTER 5 DISTRIBUTED GIT 121 This is called a refspec See Chapter 9 for a more detailed discussion of Git refspecs and different things you can do with them Next John e mails Jessica to say he s pushed some changes to the featureA branch and ask her to verify them She runs a git fetch to pull down those changes git fetch origin From jessica githost simplegit 3300904 aad881d featureA gt origin featureA Then she can see what has been changed with git log git log origin featureA featureA commit aad881d154acdaeb2b6b18ea0e827ed8a6d671e6 Author John Smith jsmithgexample com Date Fri May 29 19 57 33 2009 0700 changed log output to 30 from 25 Finally she merges John s work into her own featureA branch git checkout featureA Switched to branch featureA git merge origin featureA Updating 3300904 aad881d Fast forward lib simplegit rb 10 1 files changed 9 insertions 1 deletions Jessica wants to tweak something so she commits
258. mand takes a path name for either a file or a directory if it s a directory the command adds all the files in that directory recursively Staging Modified Files Let s change a file that was already tracked If you change a previously tracked file called benchmarks rb and then run the status command again you get something that looks like this git status On branch master Changes to be committed use git reset HEAD lt file gt to unstage new file README Changed but not updated use git add file to update what will be committed modified benchmarks rb He ct it oit it He HE HE CHAPTER 2 GIT BASICS 19 The benchmarks rb file appears under a section named Changed but not updated which means that a file that is tracked has been modified in the working directory but not yet staged To stage it you run the git add command it s a multipurpose command you use it to begin tracking new files to stage files and to do other things like marking merge conflicted files as resolved Let s run git add now to stage the benchmarks rb file and then run git status again git add benchmarks rb git status On branch master Changes to be committed use git reset HEAD lt file gt to unstage new file README modified benchmarks rb He HE HE HE Both files are staged and will go into your next commit At this point suppose you remem ber one little change that you want to make
259. mand with a character This is useful if you write your own tools that work with a Git repository I can demonstrate by aliasing git visualto run gitk git config global alias visual gitk Summary At this point you can do all the basic local Git operations creating or cloning a repository making changes staging and committing those changes and viewing the history of all the changes the repository has been through Next I ll cover Git s killer feature its branching model CHAPTER 3 Git Branching N early every VCS has some form of branching support Branching means you diverge from the main line of development and continue to do work without messing with that main line In many VCS tools this is a somewhat expensive process often requiring you to create a new copy of your source code directory which can take a long time for large projects Some people refer to the branching model in Git as its killer feature and it certainly sets Git apart in the VCS community Why is it so special The way Git branches is incredibly lightweight making branching operations nearly instantaneous and switching back and forth between branches generally just as fast Unlike many other VCSs Git encourages a workflow that branches and merges often even multiple times in a day Understanding and mastering this feature gives you a powerful and unique tool and can literally change the way that you develop What a Branch Is To really unde
260. mbers generating 141 C cached option 25 cacheinfo option 226 cat file command 225 Centralized Version Control Systems CVCSs 3 107 centralized workflows 107 108 259 260 INDEX changes committing 23 24 integrating 130 135 140 undoing 32 34 viewing 20 23 134 checkout command 50 53 checksums 7 186 cherry picks 139 140 client configuration 176 178 client side hooks 190 192 199 201 clone command 16 83 204 205 color settings 178 179 color setting 178 color ui setting 178 command aliases 44 45 commit access 111 commit command 23 24 230 amend option 157 a option 24 commit guidelines 111 112 commit history revising 156 162 using GUI to visualize 31 viewing 26 32 commit msg hook 191 199 commit objects 228 230 commit process 47 commits branch references 145 changing last 32 33 156 changing multiple 157 158 debugging 162 164 enforcing format for 194 195 excluding 134 filter branch command and 160 162 guidelines for 111 112 merging 55 57 ranges of 147 149 referencing 143 147 removing file from 161 reordering 158 reviewing 134 splitting 160 squashing 159 160 summary of 142 committed state 8 commit template configuration value 176 177 committer 29 committing workflow hooks 191 commit tree 228 config command 11 12 175 config file 11 175 224 configuration 11 basic client 176 178 colors 178 179 diff tools 179 181 external mer
261. merge it into one of your branches or you can check out a local branch at that point if you want to inspect it Fetching and Pulling from Your Remotes As you just saw to get data from your remote projects you can run git fetch remote name The command goes out to that remote project and pulls down all the data from that remote project that you don t have yet After you do this you should have references to all the branches from that remote which you can merge in or inspect at any time I ll go over what branches are and how to use them in much more detail in Chapter 3 If you cloned a repository the command automatically adds that remote repository under the name origin So git fetch origin fetches any new work that has been pushed to that server since you cloned or last fetched from it It s important to note that the fetch command pulls the data to your local repository it doesn t automatically merge it with any of your work or modify what you re currently working on You have to merge it manually into your work when you re ready If you have a branch set up to track a remote branch see the next section and Chapter 3 for more information you can use the git pull command to automatically fetch and then merge a remote branch into your current branch This may be an easier or more comfortable workflow for you and by default the git clone command automatically sets up your local master branch to track the remote master branch on t
262. merged them back into master When you dcommit you see output like this git svn dcommit Committing to file tmp test svn trunk M CHANGES txt Committed r85 M CHANGES txt r85 Abfebeec434d156c36f2bcd18F4e3d97dc3269a2 trunk No changes between current HEAD and refs remotes trunk Resetting to the latest refs remotes trunk COPYING txt locally modified INSTALL txt locally modified M COPYING txt M INSTALL txt Committed r86 M INSTALL txt M COPYING txt 186 2647f6b86ccfcaad4ec58c520e369ec81f7c283c trunk No changes between current HEAD and refs remotes trunk Resetting to the latest refs remotes trunk Running dcommit on a branch with merged history works fine except that when you look at your Git project history it hasn t rewritten either of the commits you made on the experiment branch instead all those changes appear in the SVN version of the single merge commit When someone else clones that work all they see is the merge commit with all the work squashed into it they don t see the commit data about where it came from or when it was committed Subversion Branching Branching in Subversion isn t the same as branching in Git if you can avoid using it much that s probably best However you can create and commit to branches in Subversion using git svn Creating a New SVN Branch To create a new branch in Subversion you run git svn branch branchname git svn branch opera Copying file
263. mit containing that message and makes it your new last commit If you ve committed and then you want to change the snapshot you committed by adding or changing files possibly because you forgot to add a newly created file when you originally committed the process works basically the same way You stage the changes you want by edit ing a file and running git add onit or git rmto a tracked file and the subsequent git commit amend takes your current staging area and makes it the snapshot for the new commit You need to be careful with this technique because amending changes the SHA 1 of the commit It s like a very small rebase don t amend your last commit if you ve already pushed it Changing Multiple Commit Messages To modify a commit that is farther back in your history you must move to more complex tools Git doesn t have a modify history tool but you can use the rebase tool to rebase a series of commits onto the HEAD they were originally based on instead of moving them to another one With the interactive rebase tool you can then stop after each commit you want to modify and change the message add files or do whatever you wish You can run rebase interactively by adding the i option to git rebase You must indicate how far back you want to rewrite com mits by telling the command which commit to rebase onto For example if you want to change the last three commit messages or any of the com mit messages in that group you su
264. most basic is the Local protocol in which the remote repository is in another directory on disk This is often used if everyone on your team has access to a shared filesystem such as an NFS mount or in the less likely case that everyone logs in to the same computer The latter wouldn t be ideal because all your code repository instances would reside on the same com puter making a catastrophic loss much more likely If you have a shared mounted filesystem then you can clone push to and pull from a local file based repository To clone a repository like this or to add one as a remote to an existing project use the path to the repository as the URL For example to clone a local reposi tory you can run something like this git clone opt git project git Or you can do this git clone file opt git project git Git operates slightly differently if you explicitly specify file at the beginning of the URL If you just specify the path Git tries to use hardlinks or directly copy the files it needs If you specify file Git fires up the processes that it normally uses to transfer data over a network which is generally a lot less efficient method of transferring the data The main rea son to specify the file prefix is if you want a clean copy of the repository with extraneous references or objects left out generally after an import from another version control system or something similar see Chapter 9 for maintenance tasks You
265. mote branch you can easily use the first version with a different local branch name git checkout b sf origin serverfix Branch sf set up to track remote branch refs remotes origin serverfix Switched to a new branch sf Now your local branch sf will automatically push to and pull from origin serverfix Deleting Remote Branches Suppose you re done with a remote branch say you and your collaborators are finished with a feature and have merged it into your remote s master branch or whatever branch your stable codeline is in You can delete a remote branch using the rather obtuse syntax git push remotename branch If you want to delete your serverfix branch from the server you run the following git push origin serverfix To git github com schacon simplegit git deleted serverfix Boom No more branch on your server You may want to dog ear this page because you ll need that command and you ll likely forget the syntax A way to remember this command is by recalling the git push remotename localbranch remotebranch syntax that I went over a bit earlier If you leave off the localbranch portion then you re basically saying Take nothing on my side and make it be remotebranch 70 CHAPTER 3 GIT BRANCHING Rebasing In Git there are two main ways to integrate changes from one branch into another the merge and the rebase In this section you ll learn what rebasing is how to do it why it s a pretty amazing
266. move your tmp rack directory back into the empty directory Subtree Merging Now that you ve seen the difficulties of the submodule system let s look at an alternate way to solve the same problem When Git merges it looks at what it has to merge together and then chooses an appropriate merging strategy to use If you re merging two branches Git uses a recursive strategy If you re merging more than two branches Git picks the octopus strategy These strategies are automatically chosen for you because the recursive strategy can handle complex three way merge situations for example more than one common ancestor but it can only handle merging two branches The octopus merge can handle multiple branches but is more cautious to avoid difficult conflicts so it s chosen as the default strategy if you re trying to merge more than two branches However there are other strategies you can choose as well One of them is the subtree merge and you can use it to deal with the subproject issue Here you ll see how to do the same rack embedding as in the last section but using subtree merges instead The idea of the subtree merge is that you have two projects and one ofthe projects maps to a subdirectory of the other one and vice versa When you specify a subtree merge Git is smart enough to figure out that one is a subtree of the other and merge appropriately it s pretty amazing You first add the Rack application to your project You add the Rac
267. moving Files To remove a file from Git you have to remove it from your tracked files more accurately remove it from your staging area and then commit The git rm command does that and also removes the file from your working directory so you don t see it as an untracked file next time around If you simply remove the file from your working directory it shows up under the Changed but not updated that is unstaged area of your git status output rm grit gemspec git status On branch master T Changed but not updated use git add rm lt file gt to update what will be committed if deleted grit gemspec CHAPTER 2 GIT BASICS 25 Then if you run git rm it stages the file s removal git rm grit gemspec rm grit gemspec git status On branch master Changes to be committed use git reset HEAD lt file gt to unstage deleted grit gemspec The next time you commit the file will be gone and no longer tracked If you modified the file and added it to the index already you must force the removal with the f option This is a safety feature to prevent accidental removal of data that hasn t yet been recorded in a snap shot and that can t be recovered from Git Another useful thing you may want to do is to keep the file in your working tree but remove it from your staging area In other words you may want to keep the file on your hard drive but not have Git track it
268. n 2 temporal To build and install the C Protocol Buffer runtime and the Protocol 2 temporal Buffer compiler protoc execute the following 2 temporal N NNN Again it doesn t show commits that you did locally in Git or that have been pushed to Subversion in the meantime SVN Server Information You can also get the same sort of information that svn info gives you by running git svn info git svn info Path URL https schacon test googlecode com svn trunk Repository Root https schacon test googlecode com svn Repository UUID 4c93b258 373f 11de be05 5f7a86268029 Revision 87 212 CHAPTER 8 GIT AND OTHER SYSTEMS Node Kind directory Schedule normal Last Changed Author schacon Last Changed Rev 87 Last Changed Date 2009 05 02 16 07 37 0700 Sat 02 May 2009 This is like blame and log in that it runs offline and is up to date only as of the last time you communicated with the Subversion server Ignoring What Subversion Ignores If you clone a Subversion repository that has svn ignore properties set anywhere you ll likely want to set corresponding gitignore files so you don t accidentally commit files that you shouldn t git svn has two commands to help with this issue The first is git svn create ignore which automatically creates corresponding gitignore files for you so your next commit can include them The second command isgit svn show ignore which prints to stdout the lines you need to put i
269. n nection with the Work Creative Commons will not be liable to You or any party on any legal theory for any damages whatsoever including without limitation any general special inci dental or consequential damages arising in connection to this license Notwithstanding the foregoing two 2 sentences if Creative Commons has expressly identified itself as the Licensor hereunder it shall have all rights and obligations of Licensor 258 APPENDIX CREATIVE COMMONS LEGAL CODE Except for the limited purpose of indicating to the public that the Work is licensed under the CCPL Creative Commons does not authorize the use by either party of the trademark Creative Commons or any related trademark or logo of Creative Commons without the prior written consent of Creative Commons Any permitted use will be in compliance with Creative Commons then current trademark usage guidelines as may be published on its website or otherwise made available upon request from time to time For the avoidance of doubt this trademark restriction does not form part of this License Creative Commons may be contacted at http creativecommons org Index Numbers and Symbols 0 9 20 3 option 132 asterisk 20 61 backslash 25 caret 147 149 exclamation point 45 pipe 195 question mark 20 tilde 20 147 A abc 20 access read only unauthenticated 95 96 access control with Gitosis 91 95 access control list ACL
270. n be set to do all sorts of fun things The original commit message for this functionality gives a simple example of running all your C source code through the indent program before committing You can set it up by set ting the filter attribute in your gitattributes file to filter c files with the indent filter e filter indent Then tell Git what the indent filter does on smudge and clean git config global filter indent clean indent git config global filter indent smudge cat Staging Area Working Directory git checkout Figure 7 2 The smudge filter is run on checkout 188 CHAPTER 7 CUSTOMIZING GIT Staging Area Working Directory txt Filter git add Figure 7 3 The clean filter is run when files are staged In this case when you commit files that match c Git will run them through the indent pro gram before it commits them and then run them through the cat program before it checks them back out onto disk The cat program is basically a no op it spits out the same data that it gets in This combination effectively filters all C source code files through indent before committing Another interesting example gets Date keyword expansion RCS style To do this prop erly you need a small script that takes a file through stdin figures out the last commit date for this project and inserts the date into the file Here is a small Ruby script that does that usr bin
271. n master Figure 5 9 Jessica s history after merging John s changes Now origin master is reachable from Jessica s master branch so she should be able to successfully push assuming John hasn t pushed again in the meantime git push origin master To jessica githost simplegit git 72bbc59 8059c15 master gt master Each developer has committed a few times and merged each other s work successfully see Figure 5 10 C 8059c 4 4b078 origin master Figure 5 10 Jessica s history after pushing all changes back to the server 117 118 CHAPTER 5 DISTRIBUTED GIT That is one of the simplest workflows You work for a while generally in a topic branch and merge into your master branch when it s ready to be integrated When you want to share that work you merge it into your own master branch then fetch and merge origin master if it has changed and finally push to the master branch on the server The general sequence is something like that shown in Figure 5 11 Jessica git clone url h eS Jessica Figure 5 11 General sequence of events for a simple multiple developer Git workflow Private Managed Team In this next scenario you ll look at contributor roles in a larger private group You ll learn how to work in an environment where small groups collaborate on features and then those team based contributions are integrated by another party Let s say th
272. n or will be released They have another parallel branch named develop or next that they work from or use to test stability it isn t necessarily always stable but whenever it gets to a stable state it can be merged into master It s used to pull in topic branches short lived branches like your earlier iss53 branch when they re ready to make sure they pass all the tests and don t introduce bugs In reality I m talking about pointers moving up the line of commits you re making The stable branches are farther down the line in your commit history and the bleeding edge branches are farther up the history see Figure 3 18 Figure 3 18 More stable branches are generally farther down the commit history It s generally easier to think about them as work silos where sets of commits graduate to a more stable silo when they re fully tested see Figure 3 19 develop topic Figure 3 19 It may be helpful to think of your branches as silos CHAPTER 3 GIT BRANCHING 63 You can keep doing this for several levels of stability Some larger projects also have a proposed or pu proposed updates branch that has integrated branches that may not be ready to go into the next or master branch The idea is that your branches are at various levels of stability when they reach a more stable level they re merged into the branch above them Again having multiple long running branches isn t necessary but it
273. n top of your current master or develop and so on branch If that works well you can fast forward your master branch and you ll end up with a lin ear project history The other way to move introduced work from one branch to another is to cherry pick it A cherry pick in Git is like a rebase for a single commit It takes the patch that was introduced in a commit and tries to reapply it on the branch you re currently on This is useful if you have a number of commits on a topic branch and you want to integrate only one of them or if you only have one commit on a topic branch and you d prefer to cherry pick it rather than run rebase For example suppose you have a project that looks like Figure 5 26 master On oe udin af Figure 5 26 Example history before a cherry pick If you want to pull commit e43a6 into your master branch you can run git cherry pick e43a6fd3e94888d76779ad79fb568ed180e5 fcdf Finished one cherry pick master created a0a41a9 More friendly message when locking the index fails 3 files changed 17 insertions 3 deletions This pulls the same change introduced in e43a6 but you get a new commit SHA 1 value because the date applied is different Your history looks like Figure 5 27 140 CHAPTER 5 DISTRIBUTED GIT Figure 5 27 History after cherry picking a commit on a topic branch Now you can remove your topic branch and drop the commits you didn t want to pull in
274. n you run git commit set the commit template configuration value git config global commit template HOME gitmessage txt git commit Then your editor will open to something like this for your placeholder commit message when you commit CHAPTER 7 CUSTOMIZING GIT 177 subject line what happened ticket X Please enter the commit message for your changes Lines starting with will be ignored and an empty message aborts the commit On branch master Changes to be committed use git reset HEAD lt file gt to unstage modified lib test rb git COMMIT EDITMSG 14L 297C If you have a commit message policy in place then putting a template for that policy on your system and configuring Git to use it by default can help increase the chance of that policy being followed regularly core pager The core pager setting determines what pager is used when Git pages output such as log and diff You can set it to more or to your favorite pager by default it s less or you can turn it off by setting it to a blank string git config global core pager If you run that Git will show the entire output of all commands without paging no matter how long they are user signingkey If you re making signed annotated tags as discussed in Chapter 2 setting your GPG signing key as a configuration setting makes things easier Set your key ID like so git config global user signingkey lt gpg
275. na gitignore file so you can redirect the output into your project exclude file git svn show ignore git info exclude That way you don t litter the project with gitignore files This is a good option if you re the only Git user on a Subversion team and your teammates don t want gitignore files in the project Git Svn Summary The git svn tools are useful if you re stuck with a Subversion server for now or are otherwise in a development environment that necessitates running a Subversion server You should con sider it crippled Git however or you ll hit issues in translation that may confuse you and your collaborators To stay out of trouble try to follow these guidelines Keepa linear Git history that doesn t contain merge commits made by git merge Rebase any work you do outside of your mainline branch back onto it don t merge it in Don t set up and collaborate on a separate Git server Possibly have one to speed up clones for new developers but don t push anything to it that doesn t have a git svn id entry You may even want to add a pre receive hook that checks each commit message for a git svn id and rejects pushes that contain commits without it If you follow those guidelines working with a Subversion server can be more bearable However if it s possible to move to a real Git server doing so can gain your team a lot more Migrating to Git If you have an existing codebase in another VCS but you ve decided to st
276. named git packed refs that looks like this cat git packed refs pack refs with peeled cac0cab538b970a37ea1e769cbbde608743bc96d refs heads experiment ab1afef80fac8e34258ff41fc1b867c702daa24b refs heads master cac0cab538b970a37ea1e769cbbde608743bc96d refs tags v1 0 9585191f37f7b0fb9444f35a9bf50dei91beadc2 refs tags v1 1 1a410efbd13591db07496601ebc7a059dd55cfe9 If you update a reference Git doesn t edit this file but instead writes a new file to refs heads To get the appropriate SHA for a given reference Git checks for that reference in the refs directory and then checks the packed refs file as a fallback However if you can t find a reference in the refs directory it s probably in your packed refs file Notice the last line of the file which begins with a This means the tag directly above is an annotated tag and that line is the commit that the annotated tag points to Data Recovery At some point in your Git journey you may accidentally lose a commit Generally this hap pens because you force delete a branch that had work on it and it turns out you wanted the branch after all or you hard reset a branch thus abandoning commits that you wanted some thing from Assuming this happens how can you get your commits back Here s an example that hard resets the master branch in your test repository to an older commit and then recovers the lost commits First let s review where your repository is at this point git log pre
277. nates list for http github com schacon simplegit progit git Getting pack list for http github com schacon simplegit progit git Getting index for pack 816a9b2334da9953e530f27bcac22082a9f5b835 Getting pack 816a9b2334da9953e530f27bcac22082a9f5b835 which contains cfda3bf379e4f8dba8717dee55aab78aef7f4daf walk 085bb3bcb608e1e8451d4b2432f8ecbe6306e7e7 walk a11bef06a3f659402fe7563abf99ad00de2209e6 The Smart Protocol The HTTP method is simple but a bit inefficient Using smart protocols is a more common method of transferring data These protocols have a process on the remote end that is intelli gent about Git it can read local data and figure out what the client has or needs and generate custom data for it There are two sets of processes for transferring data a pair for uploading data and a pair for downloading data Uploading Data To upload data to a remote process Git uses the send pack and receive pack processes The send pack process runs on the client and connects to a receive pack process on the remote side For example say you run git push origin master in your project and origin is defined as a URL that uses the SSH protocol Git fires up the send pack process which initiates a con nection over SSH to your server It tries to run a command on the remote server via an SSH call that looks something like this n ssh x git github com git receive pack schacon simplegit progit git 005bca82a6dff817ec6614437202690a39376394
278. nch because you no longer need it the master branch points at the same place You can delete it with the d option to git branch git branch d hotfix Deleted branch hotfix 3a0874c Now you can switch back to your work in progress branch on issue 53 and continue working on it see Figure 3 15 git checkout iss53 Switched to branch iss53 vim index html git commit a m finished the new footer issue 53 iss53 created ad82d7a finished the new footer issue 53 1 files changed 1 insertions 0 deletions It s worth noting here that the work you did in your hotfix branch is not contained in the files in your iss53 branch If you need to pull it in you can merge your master branch into your iss53 branch by running git merge master or you can wait to integrate those changes until you decide to pull the iss53 branch back into master later CHAPTER 3 GIT BRANCHING 57 master GJ 9 Figure 3 15 Your iss53 branch can move forward independently Basic Merging Suppose you ve decided that your issue 453 work is complete and ready to be merged into your master branch In order to do that you ll merge in your 1ss53 branch much like you merged in your hotfix branch earlier All you have to do is check out the branch you wish to merge into and then run the git merge command git checkout master git merge iss53 Merge made by recursive README 1 1 files changed 1 insertions 0 de
279. nd Data Recovery Occasionally you may have to do some cleanup make a repository more compact clean up an imported repository or recover lost work This section will cover some of these scenarios Maintenance Occasionally Git automatically runs a command called auto gc Most of the time this com mand does nothing However if there are too many loose objects objects not in a packfile or too many packfiles Git launches a full fledged git gc command The gc stands for garbage collect and the command does a number of things it gathers up all the loose objects and places them in packfiles it consolidates packfiles into one big packfile and it removes objects that aren t reachable from any commit and are a few months old You can run auto gc manually as follows git gc auto Again this generally does nothing You must have around 7 000 loose objects or more than 50 packfiles for Git to fire up a real gc command You can modify these limits with the gc auto and gc autopacklimit config settings respectively The other thing gc will do is pack up your references into a single file Suppose your repos itory contains the following branches and tags find git refs type f git refs heads experiment CHAPTER 9 GIT INTERNALS 245 git refs heads master git refs tags v1 0 git refs tags v1 1 If you run git gc you ll no longer have these files in the refs directory Git will move them for the sake of efficiency into a file
280. next section If you re taking patches over e mail prepared by git format patch then some of these may be helpful to you The first hook that is run is applypatch msg It takes a single argument the name of the temporary file that contains the proposed commit message Git aborts the patch if this script exits non zero You can use this to make sure a commit message is properly formatted or to normalize the message by having the script edit it in place 192 CHAPTER 7 CUSTOMIZING GIT The next hook to run when applying patches via git amis pre applypatch It takes no arguments and is run after the patch is applied so you can use it to inspect the snapshot before making the commit You can run tests or otherwise inspect the working tree with this script If something is missing or the tests don t pass exiting non zero also aborts the git am script without committing the patch The last hook to run during a git am operation is post applypatch You can use it to notify a group or the author of the patch you pulled in that you ve done so You can t stop the patch ing process with this script Other Client Hooks The pre rebase hook runs before you rebase anything and can halt the process by exiting non zero You can use this hook to disallow rebasing any commits that have already been pushed The example pre rebase hook that Git installs does this although it assumes that next is the name of the branch you publish You ll likely need to chang
281. ng 16 80 83 commit data in 48 creating on GitHub 99 101 exporting 189 190 file based 80 initializing in existing directory 15 local 80 maintenance on 244 245 moving files in 25 26 public access to 88 89 recording changes to 16 26 remote See remote repositories removing files from 24 25 SSH access 85 88 request pull command 124 resolved option 132 reuseaddr option 95 revision selection 143 149 commit ranges 147 149 multiple points 149 single revisions 143 147 rev list command 248 rm command 24 25 38 S send pack process 242 243 server configuration 183 generating SSH public key 85 86 network protocols 79 83 public access to 88 89 putting bare repository on 84 running 79 setting up 83 84 small setups 85 91 SSH access 85 88 web static 88 server side hooks 190 199 SHA 1 checksum 186 SHA 1 hash 7 143 144 225 SHA syntax 201 shortlog command 142 short SHA 143 144 show ref command 205 signed tags 40 since option 30 single revisions 143 147 smart protocols 242 244 snapshots 47 source installing Git from 9 squash option 126 172 SSH access 85 88 SSH protocol 81 SSH public key generating 85 86 SSH transfer protocol 16 staged files unstaging 33 34 staged state 8 staging area 8 24 files 150 152 of modified files 18 19 patches 152 153 standard layout 205 stash command 153 155 stash apply command 155 stash drop command 155 stashes stash
282. ng a sort of changelog of what has been added to your proj ect since your last release or e mail is to use the git shortlog command It summarizes all the commits in the range you give it for example the following gives you a summary of all the commits since your last release if your last release was named v1 0 1 git shortlog no merges master not v1 0 1 Chris Wanstrath 8 Add support for annotated tags to Grit Tag Add packed refs annotated tag support Add Grit Commitito patch Update version and History txt Remove stray puts Make 1s tree ignore nils Tom Preston Werner 4 fix dates in history dynamic version method Version bump to 1 0 2 Regenerated gemspec for version 1 0 2 You get a clean summary of all the commits since v1 0 1 grouped by author that you can e mail to your list Summary You should feel fairly comfortable contributing to a project in Git as well as maintaining your own project or integrating other users contributions Congratulations on being an effective Git developer In the next chapter you ll learn more powerful tools and tips for dealing with complex situations which will truly make you a Git master CHAPTER 6 Git Tools B now you ve learned most of the day to day commands and workflows that you need to manage or maintain a Git repository for your source code control You ve accomplished the basic tasks of tracking and committing files and you ve harnessed the power of the staging
283. nication to the public of the per formances of the Work including by public digital performance to broadcast and rebroadcast the Work by any means including signs sounds or images j Reproduce means to make copies of the Work by any means including without limitation by sound or visual recordings and the right of fixation and reproducing fixations of the Work including storage of a protected performance or phonogram in digital form or other electronic medium 2 Fair Dealing Rights Nothing in this License is intended to reduce limit or restrict any uses free from copyright or rights arising from limitations or exceptions that are provided for in connection with the copyright protection under copyright law or other applicable laws 3 License Grant Subject to the terms and conditions of this License Licensor hereby grants You a worldwide royalty free non exclusive perpetual for the duration of the applicable copyright license to exercise the rights in the Work as stated below a to Reproduce the Work to incorporate the Work into one or more Collections and to Reproduce the Work as incorporated in the Collections b to create and Reproduce Adaptations provided that any such Adaptation including any translation in any medium takes reasonable steps to clearly label demarcate or otherwise identify that changes were made to the original Work For example a translation could be marked The original work was translated fro
284. ning on your system and finally explain how to set it up so you can start working with Git At the end of this chapter you should understand why Git exists and why you should use it and you should be ready to do so About Version Control What is version control and why should you care Version control is a system that records changes to a file or set of files over time so that you can recall specific versions later For the examples in this book you will use software source code as the files being version controlled though in reality you can do this with nearly any type of file on a computer If you are a graphic or web designer and want to keep every version of an image or layout which you would most certainly want to a Version Control System VCS is a very wise thing to use It allows you to revert files back to a previous state revert the entire project back to a previous state compare changes over time see who last modified something that might be causing a problem who introduced an issue and when and more Using a VCS also generally means that if you screw things up or lose files you can easily recover In addition you get all this for very little overhead CHAPTER 1 GETTING STARTED Local Version Control Systems Many people s version control method of choice is to copy files into another directory per haps a time stamped directory if they re clever This approach is very common because it s so simple but it s a
285. nly option to the git log command mentioned briefly in Chapter 2 git log 1 name only pretty format 9f585d README lib test rb If you use the ACL structure returned from the get_acl_access_data method and check it against the listed files in each of the commits you can determine whether the user has access to push all of their commits only allows certain users to modify certain subdirectories in a project def check directory perms access get acl access data acl see if anyone is trying to push something they can t new commits git rev list oldrev newrev split n new commits each do rev files modified git log 1 name only pretty format rev split n files modified each do path next if path size has file access false access user each do access path if laccess path user has access to everything path index access path 0 access to this path has file access true end CHAPTER 7 CUSTOMIZING GIT 197 end if has file access puts POLICY You do not have access to push to path exit 1 end end end end check directory perms Most of that should be easy to follow You get a list of new commits being pushed to your server with git rev list Then for each of those you find which files are modified and make sure the user who s pushing has access to all the paths being modified One Rubyism that may not be clear is path index access path 0 which is
286. nt of the Adaptation to exercise the rights granted to that recipient under the terms of the Applicable License You must keep intact all notices that refer to the Applicable License and to the disclaimer of warranties with every copy of the Work as included in the Adaptation You Distribute or Publicly Perform When You Distribute or Publicly Perform the Adaptation You may not impose any effective technological measures on the Adaptation that restrict the ability of a recipient of the Adaptation from You to exercise the rights granted to that recipient under the terms of the Applicable License This Section 4 b applies to the Adaptation as incorporated in a Collection but this does not require the Collection apart from the Adaptation itself to be made subject to the terms of the Applicable License c You may not exercise any of the rights granted to You in Section 3 above in any manner that is primarily intended for or directed toward commercial advantage or private monetary compensation The exchange of the Work for other copy righted works by means of digital file sharing or otherwise shall not be considered to be intended for or directed toward commercial advantage or private monetary compensation provided there is no payment of any monetary compensation in connection with the exchange of copyrighted works APPENDIX CREATIVE COMMONS LEGAL CODE 255 d If You Distribute or Publicly Perform the Work or any Adaptations or Collec tions You mu
287. o Subversion and want to see your history in SVN output style you can run git svn logto view your commit history in SVN formatting git svn log r87 schacon 2009 05 02 16 07 37 0700 Sat 02 May 2009 2 lines autogen change CHAPTER 8 GIT AND OTHER SYSTEMS 211 r86 schacon 2009 05 02 16 00 21 0700 Sat 02 May 2009 2 lines Merge branch experiment r85 schacon 2009 05 02 16 00 09 0700 Sat 02 May 2009 2 lines updated the changelog You should know two important things about git svn log First it works offline unlike the real svn log command which asks the Subversion server for the data Second it only shows you commits that have been committed up to the Subversion server Local Git commits that you haven t dcommited don t show up neither do commits that people have made to the Subversion server in the meantime It s more like the last known state of the commits on the Subversion server SVN Annotation Much as the git svn log command simulates the svn log command offline you can get the equivalent of svn annotate by running git svn blame FILE The output looks like this git svn blame README txt temporal Protocol Buffers Google s data interchange format temporal Copyright 2008 Google Inc temporal http code google com apis protocolbuffers temporal 22 temporal C Installation Unix 22 temporal 2 temporal 79 schacon Committing in git svn 78 schaco
288. o a branch named featureA and he can look at it now While she waits for feedback from John Jessica decides to start working on featureB with Josie To begin she starts a new feature branch basing it off the server s master branch it Jessica s Machine git fetch origin git checkout b featureB origin master Switched to a new branch featureB Now Jessica makes a couple of commits on the featureB branch vim lib simplegit rb git commit am made the ls tree function recursive featureB e5bOfdc made the ls tree function recursive 1 files changed 1 insertions 1 deletions vim lib simplegit rb git commit am add ls files featureB 8512791 add ls files 1 files changed 5 insertions O deletions 120 CHAPTER 5 DISTRIBUTED GIT Jessica s repository looks like Figure 5 12 ae T 7 apie gu 85127 Figure 5 12 Jessica s initial commit history She s ready to push up her work but she gets an e mail from Josie that a branch with some initial work on it was already pushed to the server as featureBee Jessica first needs to merge those changes in with her own before she can push to the server She can then fetch Josie s changes down with git fetch git fetch origin From jessica githost simplegit new branch featureBee origin featureBee Jessica can now merge this into the work she did with git merge git merge origin featureBee Auto merging lib simplegit rb Merge
289. o add a project Let s use gitserver as the hostname of the server on which you ve set up your git user and repository If you re running it internally and you set up DNS for gitserver to point to that server then you can use the commands pretty much as is on Johns computer cd myproject git init git add git commit m initial commit git remote add origin gitGgitserver opt git project git git push origin master At this point the others can clone it down and push changes back up just as easily git clone git gitserver opt git project git vim README git commit am fix for the README file git push origin master 88 CHAPTER 4 GIT ON THE SERVER With this method you can quickly get a read write Git server up and running for a hand ful of developers As an extra precaution you can easily restrict the git user to only doing Git activities with a limited shell tool called git shell that comes with Git If you set this as your git user s login shell then the git user can t have normal shell access to your server To use this specify git shell instead of bash or csh for your user s login shell To do so you ll likely have to edit your etc passwd file sudo vim etc passwd At the bottom you should find a line that looks something like this git x 1000 1000 home git bin sh Change bin sh to usr bin git shell or run which git shellto see where it s installed The line should l
290. o continue to the next patch fix the file git add ticgit gemspec git am resolved Applying seeing if this helps the gem If you want Git to try a bit more intelligently to resolve the conflict you can pass a 3 option to it which makes Git attempt a three way merge This option isn t on by default because it doesn t work if the commit the patch says it was based on isn t in your repository If you do have that commit if the patch was based on a public commit then the 3 option is generally much smarter about applying a conflicting patch git am 3 0001 seeing if this helps the gem patch Applying seeing if this helps the gem error patch failed ticgit gemspec 1 error ticgit gemspec patch does not apply Using index info to reconstruct a base tree Falling back to patching base and 3 way merge No changes Patch already applied CHAPTER 5 DISTRIBUTED GIT 133 In this case I was trying to apply a patch I had already applied Without the 3 option it looks like a conflict If you re applying a number of patches from an mbox you can also run the am command in interactive mode which stops at each patch it finds and asks if you want to apply it git am 3 i mbox Commit Body is Apply y es n o e dit v iew patch a ccept all This is nice if you have a number of patches saved because you can view the patch first if you don t remember what it is or not apply the patch if you ve already done so W
291. o include in what will be committed README nothing added to commit but untracked files present use git add to track 17 18 CHAPTER 2 GIT BASICS You can see that your new README file is untracked because it s under the Untracked files heading in your status output Untracked basically means that Git sees a file you didn t have in the previous snapshot commit Git won t start including it in your commit snapshots until you explicitly tell it to do so It does this so you don t accidentally begin including gener ated binary files or other files that you didn t mean to include You do want to start including the README file so let s start tracking the file Tracking New Files In order to begin tracking a new file you use the command git add To begin tracking the README file you can run this git add README If you run the status command again you can see that your README file is now tracked and staged git status On branch master Changes to be committed use git reset HEAD lt file gt to unstage new file README Gk ct You can tell that it s staged because it s under the Changes to be committed heading If you commit at this point the version of the file at the time you ran git addis what will be in the historical snapshot You may recall that when you rangit init earlier you then ran git add files that was to begin tracking files in your directory The git add com
292. o main types of tags lightweight and annotated A lightweight tag is very much like a branch that doesn t change it s just a pointer to a specific commit Annotated tags how ever are stored as full objects in the Git database They re check summed contain the tagger name e mail and date have a tagging message and can be signed and verified with GNU Pri vacy Guard GPG It s generally recommended that you create annotated tags so you can have all this information but if you want a temporary tag or for some reason don t want to keep the other information lightweight tags are available too Annotated Tags Creating an annotated tag in Git is simple The easiest way is to specify a when you run the tag command git tag a v1 4 m my version 1 4 git tag v0 1 v1 3 v1 4 The m specifies a tagging message which is stored with the tag If you don t specify a mes sage for an annotated tag Git launches your editor so you can type it in You can see the tag data along with the commit that was tagged by using the git show command git show v1 4 tag v1 4 Tagger Scott Chacon lt schacon gee mail com gt Date Mon Feb 9 14 45 11 2009 0800 40 CHAPTER 2 GIT BASICS my version 1 4 commit 15027957951b64cf874c3557a0f3547bd83b3ff6 Merge 4a447f7 a6b4c97 Author Scott Chacon lt schacon gee mail com gt Date Sun Feb 8 19 02 46 2009 0800 Merge branch experiment That shows the tagger information the d
293. o the corporate environment and help your fellow devel opers become more efficient while you lobby to get the infrastructure changed to support Git fully The Subversion bridge is the gateway drug to the DVCS world git svn The base command in Git for all the Subversion bridging commands is git svn You preface everything with that It takes quite a few commands so you ll learn about the common ones while going through a few small workflows It s important to note that when you re using git svn you re interacting with Subver sion which is a system that is far less sophisticated than Git Although you can easily do local branching and merging it s generally best to keep your history as linear as possible by rebas ing your work and avoiding doing things like simultaneously interacting with a Git remote repository Don t rewrite your history and try to push again and don t push to a parallel Git reposi tory to collaborate with fellow Git developers at the same time Subversion can have only 203 204 CHAPTER 8 GIT AND OTHER SYSTEMS a single linear history and confusing it is very easy If you re working with a team and some are using SVN and others are using Git make sure everyone is using the SVN server to collabo rate doing so will make your life easier Setting Up To demonstrate this functionality you need a typical SVN repository that you have write access to If you want to copy these examples you ll have to make a writea
294. ode which you can download from git kernel org git clone git git kernel org pub scm git git git cd git contrib fast import In this fast import directory you should find an executable Python script named git p4 You must have Python and the p4 tool installed on your machine for this import to work For example you ll import the Jam project from the Perforce Public Depot To set up your client you must export the P4PORT environment variable to point to the Perforce depot export P4PORT public perforce com 1666 Run the git p4 clone command to import the Jam project from the Perforce server sup plying the depot and project path and the path into which you want to import the project CHAPTER 8 GIT AND OTHER SYSTEMS 215 git p4 clone public jam src all opt p4import Importing from public jam src all into opt p4import Reinitialized existing Git repository in opt p4import git Import destination refs remotes p4 master Importing revision 4409 100 If you go to the opt p4import directory and run git log you can see your imported work git log 2 commit 1fd4ec126171790efd2db83548b85b1bbbco7dc2 Author Perforce staff supportGperforce com Date Thu Aug 19 10 18 45 2004 0800 Drop rc3 moniker of jam 2 5 Folded rc2 and rc3 RELNOTES into the main part of the document Built new tar zip balls Only 16 months later git p4 depot paths public jam src change 4409 commit ca8870db541a23ed867f38
295. of Git beginning with ver sion 1 6 1 you can set receive denyDeletes to true git config system receive denyDeletes true This denies branch and tag deletion over a push across the board no user can do it To remove remote branches you must remove the ref files from the server manually There are also more interesting ways to do this on a per user basis via ACLs as you ll learn at the end of this chapter 184 CHAPTER 7 CUSTOMIZING GIT Git Attributes Some of these settings can also be specified for a path so that Git applies those settings only for a subdirectory or subset of files These path specific settings are called Git attributes and are set either in a gitattribute file in one of your directories normally the root of your proj ect or in the git info attributes file if you don t want the attributes file committed with your project Using attributes you can do things like specify separate merge strategies for individual files or directories in your project tell Git how to diff non text files or have Git filter content before you check it into or out of Git In this section you ll learn about some of the attributes you can set on your paths in your Git project and see a few examples of using this feature in practice Binary Files One cool trick for which you can use Git attributes is telling Git which files are binary in cases it otherwise may not be able to figure out and giving Git special instructions about
296. of parallel contributed topic branches If the topics still need work they re merged into pu instead When it s determined that they re totally stable the topics are re merged into master and are then rebuilt from the topics that were in next but didn t yet graduate to master This means master almost always moves forward next is rebased occasionally and pu is rebased even more often see Figure 5 25 Figure 5 25 Merging contributed topic branches into long term integration branches CHAPTER 5 DISTRIBUTED GIT 139 When a topic branch has finally been merged into master it s removed from the reposi tory The Git project also has a maint branch that is forked off from the last release to provide backported patches in case a maintenance release is required Thus when you clone the Git repository you have four branches that you can check out to evaluate the project in different stages of development depending on how cutting edge you want to be or how you want to contribute and the maintainer has a structured workflow to help them vet new contributions Rebasing and Cherry Picking Workflows Other maintainers prefer to rebase or cherry pick contributed work on top of their master branch rather than merging it in to keep a mostly linear history When you have work in a topic branch and have determined that you want to integrate it you move to that branch and run the rebase command to rebuild the changes o
297. oject You then need to add in this new repository URL as a second remote in this case named myfork git remote add myfork url You need to push your work up to it It s easiest to push the remote branch you re working on up to your repository rather than merging into your master branch and pushing that up The reason is that if the work isn t accepted or is cherry picked you don t have to rewind your master branch If the maintainers merge rebase or cherry pick your work you ll eventually get it back via pulling from their repository anyhow git push myfork featureA When your work has been pushed up to your fork you need to notify the maintainer This is often called a pull request and you can either generate it via the website GitHub has a pull request button that automatically messages the maintainer or run the git request pull command and e mail the output to the project maintainer manually The request pull command takes the base branch into which you want your topic branch pulled and the Git repository URL you want them to pull from and outputs a summary of all the changes you re asking to be pulled in For instance if Jessica wants to send John a pull request and she s done two commits on the topic branch she just pushed up she can run this git request pull origin master myfork The following changes since commit 1edee6b1d61823a2de3b09c160d7080b8d1b3a40 John Smith 1 added a new function CHAPTER 5 DISTRIBU
298. ommit refs heads master puts mark mark puts committer author date 0700 export data imported from dir puts from last mark if last mark You hardcode the time zone 0700 because doing so is easy If you re importing from another system you must specify the time zone as an offset The commit message must be expressed in a special format data size n contents The format consists of the word data the size of the data to be read a newline and finally the data Because you need to use the same format to specify the file contents later you create a helper method export data def export data string print data string size n string end All that s left is to specify the file contents for each snapshot This is easy because you have each one in a directory you can print out the deleteall command followed by the con tents of each file in the directory Git will then record each snapshot appropriately puts deleteall Dir glob each do file next if File file file inline data file end Note Because many systems think of their revisions as changes from one commit to another fast import can also take commands with each commit to specify which files have been added removed or modified and what the new contents are You could calculate the differences between snapshots and provide only this data but doing so is more complex you may as well give Git all the data and let it figure i
299. on of infringement of the trademark Lead Editor Duncan Parkes Technical Reviewer Shawn Pearce Editorial Board Clay Andres Steve Anglin Mark Beckner Ewan Buckingham Tony Campbell Gary Cornell Jonathan Gennick Michelle Lowman Matthew Moodie Jeffrey Pepper Frank Pohlmann Ben Renow Clarke Dominic Shakeshaft Matt Wade Tom Welsh Project Managers Beth Christmas Candace English Copy Editor Tiffany Taylor Associate Production Director Kari Brooks Copony Production Editor Liz Berry Compositor Diana Van Winkle Proofreader Dan Shaw Indexer Julie Grady Cover Designer Anna Ishchenko Manufacturing Director Tom Debolski Distributed to the book trade worldwide by Springer Verlag New York Inc 233 Spring Street 6th Floor New York NY 10013 Phone 1 800 SPRINGER fax 201 348 4505 e mail orders ny springer sbm com or visit http www springeronline com For information on translations please contact Apress directly at 233 Spring Street New York New York 10013 e mail info a press com or visit http www apress com Apress and friends of ED books may be purchased in bulk for academic corporate or promotional use eBook versions and licenses are also available for most titles For more information reference our Special Bulk Sales eBook Licensing web page at http www apress com info bulksales The information in this book is distributed on an as is basis without warranty Although every precau tion has b
300. on with previous behavior this is a good guideline to follow It s also a good idea to use the imperative present tense in these messages In other words use commands Instead of I added tests for or Adding tests for use Add tests for Here is a template originally written by Tim Pope at tpope net Short 50 chars or less summary of changes More detailed explanatory text if necessary Wrap it to about 72 characters or so In some contexts the first line is treated as the subject of an email and the rest of the text as the body The blank line separating the summary from the body is critical unless you omit the body entirely tools like rebase can get confused if you run the two together Further paragraphs come after blank lines Bullet points are okay too Typically a hyphen or asterisk is used for the bullet preceded by a single space with blank lines in between but conventions vary here If all your commit messages look like this things will be a lot easier for you and the devel opers you work with The Git project has well formatted commit messages I encourage you torun git log no merges there to see what a nicely formatted project commit history looks like In the following examples and throughout most of this book for the sake of brevity I don t format messages nicely like this instead I use the m option to git commit Do as I say not as I do Private Small Team The simplest setup y
301. ood time to add your public SSH key as well I covered how to generate a new key earlier in the Small Setups section Take the contents of the pub lic key of that pair and paste it into the SSH Public Key text box Clicking the explain ssh keys link takes you to detailed instructions on how to do so on all major operating systems Clicking the I agree sign me up button takes you to your new user dashboard see Figure 4 4 testinguser account profile log o github Search g account profile log out SOCIAL CODING Browse Guides Advanced E0 dashboard gists News Feed Your Repositories create a new one all public private sources forks for you from you git Welcome to GitHub What s next Create a Repository Find a Repository Peruse the GitHub Guides Figure 4 4 The GitHub user dashboard CHAPTER 4 GIT ON THE SERVER 99 Next you can create a new repository Creating a New Repository Start by clicking the create a new one link next to Your Repositories on the user dashboard You re taken to the Create a New Repository form see Figure 4 5 Create a New Repository Create a new empty repository into which you can push your local git repo NOTE If you intend to push a copy of a repository that is already hosted on GitHub then you should fork it instead Project Name iphone_project Description iphone project for our mobile group Homepag
302. ook scripts to enforce or encourage customized policies and using environment configura tion settings so you can work the way you want to You ll also cover building your own set of scripts to enforce a custom committing policy Chapter 8 deals with Git and other VCSs This includes using Git in a Subversion SVN world and converting projects from other VCSs to Git A lot of organizations still use SVN and aren t about to change but by this point you ll have learned the incredible power of Git and this chapter will show you how to cope if you still have to use a SVN server You ll also cover how to import projects from several different systems in case you do convince everyone to make the plunge Now that you know all about Git and can wield it with power and grace you can move on to Chapter 9 which delves into the murky yet beautiful depths of Git internals Here you ll learn how Git stores its objects what the object model is details of packfiles and server pro tocols and more Throughout the book refers to sections of this chapter in case you feel like looking deeper at that point but if you re like me and want to dive right into the technical details you may want to read Chapter 9 first I leave that up to you Let s get started xi CHAPTER 1 Getting Started This chapter is about getting started with Git We ll begin at the beginning by presenting some background about n version control tools then move on to how you get Git run
303. ook something like this git x 1000 1000 home git usr bin git shell Now the git user can only use the SSH connection to push and pull Git repositories and can t shell onto the machine If you try you ll see a login rejection ssh git gitserver fatal What do you think I am A shell Connection to gitserver closed Public Access What if you want anonymous read access to your project Perhaps instead of hosting an inter nal private project you want to host an open source project Or maybe you have a bunch of automated build servers or continuous integration servers that change a lot and you don t want to have to generate SSH keys all the time you just want to add simple anonymous read access Probably the simplest way for smaller setups is to run a static web server with its docu ment root where your Git repositories are and then enable that post update hook I mentioned in the first section of this chapter You ll work from the previous example Say you have your repositories in the opt git directory and an Apache server is running on your machine Again you can use any web server for this but as an example I ll demonstrate some basic Apache configurations that should give you an idea of what you might need First you need to enable the hook cd project git mv hooks post update sample hooks post update chmod a x hooks post update CHAPTER 4 GIT ON THE SERVER 89 If you re using a version of Git earlier than 1
304. oor grit git cho45 git github com cho45 grit git defunkt git github com defunkt grit git koke git github com koke grit git origin git github com mojombo grit git This means I can pull contributions from any of these users pretty easily But notice that only the origin remote is an SSH URL so it s the only one I can push to Ill cover why this is in Chapter 4 36 CHAPTER 2 GIT BASICS Adding Remote Repositories I ve mentioned and given some demonstrations of adding remote repositories in previous sections but here is how to do it explicitly To add a new remote Git repository as a short name you can reference easily run git remote add shortname url git remote origin git remote add pb git github com paulboone ticgit git git remote v origin git github com schacon ticgit git pb git github com paulboone ticgit git Now you can use the string pb on the command line in lieu of the whole URL For exam ple if you want to fetch all the information that Paul has but that you don t yet have in your repository you canrun git fetch pb git fetch pb remote Counting objects 58 done remote Compressing objects 100 41 41 done remote Total 44 delta 24 reused 1 delta 0 Unpacking objects 100 44 44 done From git github com paulboone ticgit new branch master gt pb master new branch ticgit gt pb ticgit Paul s master branch is accessible locally as pb master you can
305. or ignored patterns that you don t want to track in a gitignore file The hooks directory con tains your client or server side hook scripts which are discussed in detail in Chapter 6 This leaves four important entries the HEAD and index files and the objects and refs directories These are the core parts of Git The objects directory stores all the content for your database the refs directory stores pointers into commit objects in that data branches the HEAD file points to the branch you currently have checked out and the index file is where Git stores your staging area information You ll now look at each of these sections in detail to see how Git operates Git Objects Git is a content addressable filesystem Great What does that mean It means that at the core of Git is a simple key value data store You can insert any kind of content into it and it will give you back a key that you can use to retrieve the content again at any time To demonstrate you can use the plumbing command hash object which takes some data stores it in your git directory and gives you back the key the data is stored as First you initialize a new Git repository and verify that there is nothing in the objects direc tory mkdir test cd test git init Initialized empty Git repository in tmp test git find git objects git objects git objects info git objects pack find git objects type f CHAPTER 9 GIT INTERNALS 225 Git h
306. or push access or access to push updates to all the files they re modifying with the push The post receive hook runs after the entire process is completed and can be used to update other services or notify users It takes the same stdin data as the pre receive hook Examples include e mailing a list notifying a continuous integration server or updating a ticket tracking system you can even parse the commit messages to see if any tickets need to be opened modified or closed This script can t stop the push process but the client doesn t disconnect until it has completed so be careful when you try to do anything that may take a long time CHAPTER 7 CUSTOMIZING GIT 193 update The update script is very similar to the pre receive script except that it s run once for each branch the pusher is trying to update If the pusher is trying to push to multiple branches pre receive runs only once whereas update runs once per branch they re pushing to Instead of reading from stdin this script takes three arguments the name of the reference branch the SHA 1 that reference pointed to before the push and the SHA 1 the user is trying to push If the update script exits non zero only that reference is rejected other references can still be updated An Example Git Enforced Policy In this section you ll use what you ve learned to establish a Git workflow that checks for a cus tom commit message format enforces fast forward only pushes an
307. ore spaces instead of tabs and cr at eol which tells Git that carriage returns at the end of lines are OK You can tell Git which of these you want enabled by setting core whitespace to the values you want on or off separated by commas You can disable settings by either leaving them out of the setting string or prepending a in front of the value For example if you want all but cr at eol to be set you can do this git config global core whitespace trailing space space before tab indent with non tab Git will detect these issues when you run agit diff command and try to color them so you can possibly fix them before you commit It will also use these values to help you when you apply patches with git apply When you re applying patches you can ask Git to warn you if it s applying patches with the specified whitespace issues git apply whitespace warn patch Or you can have Git try to automatically fix the issue before applying the patch git apply whitespace fix patch CHAPTER 7 CUSTOMIZING GIT 183 Server Configuration Not nearly as many configuration options are available for the server side of Git but there are a few interesting ones you may want to take note of receive fsckObjects By default Git doesn t check for consistency all the objects it receives during a push Although Git can check to make sure each object still matches its SHA 1 checksum and points to valid objects it doesn t do that by de
308. ost recent version Each version of Git tends to include useful UI enhancements so getting the latest ver sion is often the best route if you feel comfortable compiling software from source It s also the case that many Linux distributions contain old packages so unless you re on a very up to date distribution or are using backports installing from source may be the best bet To install Git you need to have the following libraries that Git depends on curl zlib openssl expat and libiconv For example if you re on a system that has yum such as Fedora or apt get such as a Debian based system you can use one of these commands to install all of the dependencies yum install curl devel expat devel gettext devel openssl devel zlib devel apt get install curl devel expat devel gettext devel openssl devel zlib devel When you have all the necessary dependencies you can go ahead and grab the latest snapshot from the Git web site http git scm com download Then compile and install tar zxf git 1 6 0 5 tar gz cd git 1 6 0 5 make prefix usr local all sudo make prefix usr local install After this is done you can also get Git via Git itself for updates git clone git git kernel org pub scm git git git 9 CHAPTER 1 GETTING STARTED Installing on Linux If you want to install Git on Linux via a binary installer you can generally do so through the basic package management tool that comes with your dis
309. ost value will be imap instead of imaps When that is set up you can use git send email to place the patch series in the Drafts folder of the specified IMAP server git send email patch 0001 added 1limit to log function patch 0002 changed 1log output to 30 from 25 patch Who should the emails appear to be from Jessica Smith jessicagexample com Emails will be sent from Jessica Smith lt jessica example com gt Who should the emails be sent to jessica example com Message ID to be used as In Reply To for the first email y Then Git spits out a bunch oflog information looking something like this for each patch you re sending mbox Adding cc Jessica Smith jessicagexample com from Mine From Jessica Smith lt jessica example com gt OK Log says Sendmail usr sbin sendmail i jessica example com From Jessica Smith lt jessica example com gt To jessica example com Subject PATCH 1 2 added limit to log function Date Sat 30 May 2009 13 29 15 0700 Message Id lt 1243715356 61726 1 git send email jessica example com gt X Mailer git send email 1 6 2 rc1 20 g8c5b dirty In Reply To y References y Result OK At this point you should be able to go to your Drafts folder change the To field to the mailing list you re sending the patch to possibly CC the maintainer or person responsible for that section and send it off Summary This section has covered a number of common workflows
310. ott Chacon 2008 04 06 10 15 08 0700 17 command git log tree 9f6560e4 Scott Chacon 2008 03 17 21 52 20 0700 18 end 9f6560e4 Scott Chacon 2008 03 17 21 52 20 0700 19 42cf2861 Magnus Chacon 2008 04 13 10 45 01 0700 20 def blame path 42cf2861 Magnus Chacon 2008 04 13 10 45 01 0700 21 command git blame path 42cf2861 Magnus Chacon 2008 04 13 10 45 01 0700 22 end Notice that the first field is the partial SHA 1 of the commit that last modified that line The next two fields are values extracted from that commit the author name and the authored date of that commit so you can easily see who modified that line and when After that come the line number and the content of the file Also note the 4832fe2 commit lines which des ignate that those lines were in this file s original commit That commit is when this file was first added to this project and those lines have been unchanged since This is a tad confusing because now you ve seen at least three different ways that Git uses the to modify a commit SHA but that is what it means here Another cool thing about Git is that it doesn t track file renames explicitly It records the snapshots and then tries to figure out what was renamed implicitly after the fact One ofthe interesting features of this is that you can ask it to figure out all sorts of code movement as well If you pass C to git blame Git analyzes the file you re annotating and tries to figure out CHAP
311. ou haven t committed yet but after you commit a snapshot into Git it is very difficult to lose especially if you regularly push your database to another repository This makes using Git a joy because you know you can experiment without the danger of severely screwing things up For a more in depth look at how Git stores its data and how you can recover data that seems lost see Under the Covers in Chapter 9 7 CHAPTER 1 GETTING STARTED The Three States Now pay attention This is the main thing to remember about Git if you want the rest of your learning process to go smoothly Git has three main states that your files can reside in committed modified and staged Committed means that the data is safely stored in your local database Modified means that you have changed the file but have not committed it to your database yet Staged means that you have marked a modified file in its current version to go into your next commit snapshot This leads us to the three main sections of a Git project the Git directory the working directory and the staging area see Figure 1 6 Local Operations Working Staging Directory Area Figure 1 6 Working directory staging area and Git directory The Git directory is where Git stores the metadata and object database for your project This is the most important part of Git and it is what is copied when you clone a repository from another computer The working directory is a
312. ou re likely to encounter is a private project with one or two other devel opers By private I mean closed source not read accessible to the outside world You and the other developers all have push access to the repository In this environment you can follow a workflow similar to what you might do when using Subversion or another centralized system You still get the advantages of things like offline com mitting and vastly simpler branching and merging but the workflow can be very similar the main difference is that merges happen client side rather than on the server at commit time Let s see what it might look like when two developers start to work together with a shared repository The first developer John clones the repository makes a change and commits locally I m replacing the protocol messages with in these examples to shorten them somewhat John s Machine git clone john githost simplegit git Initialized empty Git repository in home john simplegit git CHAPTER 5 DISTRIBUTED GIT 113 cd simplegit vim lib simplegit rb git commit am removed invalid default value master 738ee87 removed invalid default value 1 files changed 1 insertions 1 deletions The second developer Jessica does the same thing clones the repository and commits a change Jessica s Machine git clone jessica githost simplegit git Initialized empty Git repository in home jessica simplegit git cd simplegit
313. our contributors develop The other advantage of this approach is that you get the history of the commits as well Although you may have legitimate merge issues you know where in your history their work is based a proper three way merge is the default rather than having to supply a 3 and hope the patch was generated off a public commit to which you have access If you aren t working with a person consistently but still want to pull from them in this way you can provide the URL of the remote repository to the git pull command This does a one time pull and doesn t save the URL as a remote reference git pull git github com onetimeguy project git From git github com onetimeguy project branch HEAD FETCH HEAD Merge made by recursive 134 CHAPTER 5 DISTRIBUTED GIT Determining What Is Introduced Now you have a topic branch that contains contributed work At this point you can determine what you d like to do with it This section revisits a couple of commands so you can see how you can use them to review exactly what you ll be introducing if you merge this into your main branch It s often helpful to get a review of all the commits that are in this branch but that aren t in your master branch You can exclude commits in the master branch by adding the not option before the branch name For example if your contributor sends you two patches and you cre ate a branch called contrib and applied those patches there you can run thi
314. output but it does happen You should now have a copy of the Git directory data in your my_project git directory This is roughly equivalent to something like cp Rf my_project git my_project git There are a couple of minor differences in the configuration file but for your purpose this is close to the same thing It takes the Git repository by itself without a working directory and creates a directory specifically for it alone Putting the Bare Repository on a Server Now that you have a bare copy of your repository all you need to do is put it on a server and set up your protocols Let s say you ve set up a server called git example com that you have SSH access to and you want to store all your Git repositories under the opt git directory You can set up your new repository by copying your bare repository over scp r my project git userggit example com opt git At this point other users who have SSH access to the same server which has read access to the opt git directory can clone your repository by running git clone userggit example com opt git my project git If a user SSHs into a server and has write access to the opt git my project git directory they also automatically have push access Git automatically adds group write permissions to a repository properly if you run thegit init command with the shared option ssh user git example com cd opt git my project git git init bare shared You see how
315. pany com My Computer origin master CIT co master Figure 3 25 Adding another server as a remote git ourcompany com git team1 ourcompany com git fetch teamone teamone maser oriin master My Computer master Figure 3 26 You get a reference to teamone s master branch position locally 68 CHAPTER 3 GIT BRANCHING Pushing When you want to share a branch with the world you need to push it up to a remote that you have write access to Your local branches aren t automatically synchronized to the remotes you write to you have to explicitly push the branches you want to share That way you can use private branches to do work you don t want to share and push up only the topic branches you want to collaborate on If you have a branch named serverfix that you want to work on with others you can push it up the same way you pushed your first branch Run git push remote branch git push origin serverfix Counting objects 20 done Compressing objects 100 14 14 done Writing objects 100 15 15 1 74 KiB done Total 15 delta 5 reused O delta 0 To git github com schacon simplegit git new branch serverfix gt serverfix This is a bit of a shortcut Git automatically expands the serverfix branch name out to refs heads serverfix refs heads serverfix which means Take my serverfix local branch and push it to update the remote s serverfix branch I ll go over
316. portant because every Git commit uses this information and it s immutably baked into the commits you pass around git config global user name John Doe git config global user email johndoe example com 12 CHAPTER 1 GETTING STARTED Again you need to do this only once if you pass the global option because then Git will always use that information for anything you do on that system If you want to override this with a different name or e mail address for specific projects you can run the command with out the global option when you re in that project Your Editor Now that your identity is set up you can configure the default text editor that will be used when Git needs you to type in a message By default Git uses your system s default editor which is generally Vi or Vim If you want to use a different text editor such as Emacs you can do the following git config global core editor emacs Your Diff Tool Another useful option you may want to configure is the default diff tool to use to resolve merge conflicts Say you want to use vimdiff git config global merge tool vimdiff Git accepts kdiff3 tkdiff meld xxdiff emerge vimdiff gvimdiff ecmerge and opendiff as valid merge tools You can also set up a custom tool see Chapter 7 for more information about doing that Checking Your Settings If you want to check your settings you can use thegit config list command to list all the settings Git
317. powerful this technique can be for customized applications You have to be careful though because the gitattributes file is committed and passed around with the project but the driver in this case dater isn t so it won t automatically work everywhere When you design these filters they should be able to fail gracefully and have the project still work properly Exporting Your Repository Git attribute data also allows you to do some interesting things when exporting an archive of your project export ignore You can tell Git not to export certain files or directories when generating an archive If there is a subdirectory or file that you don t want to include in your archive file but that you do want checked into your project you can determine that file via the export ignore attribute For example say you have some test files in a test subdirectory and it doesn t make sense to include them in the tarball export of your project You can add the following line to your Git attributes file test export ignore Now when you run git archive to create a tarball of your project that directory won t be included in the archive export subst Another thing you can do for your archives is some simple keyword substitution Git lets you put the string Format in any file with any of the pretty format formatting shortcodes many of which you saw in Chapter 2 For instance if you want to include a file named LAST _ COMMIT in your proj
318. pply as an argument to git rebase i the parent of the last commit you want to edit which is HEAD 2 or HEAD 3 It may be easier to remember the 3 because you re trying to edit the last three commits but keep in mind that you re actually des ignating four commits ago the parent of the last commit you want to edit git rebase i HEAD 3 Remember again that this is a rebasing command every commit included in the range HEAD 3 HEAD will be rewritten whether you change the message or not Don t include any commit you ve already pushed to a central server doing so will confuse other developers by providing an alternate version of the same change Running this command gives you a list of commits in your text editor that looks some thing like this pick f7f3f6d changed my name a bit pick 310154e updated README formatting and added blame pick a5f4a0d added cat file Rebase 710f0f8 a5f4a0d onto 710f0f8 Commands p pick use commit e edit use commit but stop for amending s squash use commit but meld into previous commit If you remove a line here THAT COMMIT WILL BE LOST However if you remove everything the rebase will be aborted 158 CHAPTER 6 GIT TOOLS It s important to note that these commits are listed in the opposite order than you normally see them using the log command If you run a log you see something like this git log pretty format h s HEAD 3 HEAD a5f4a0d
319. project to incorporate their changes each party can work at their own pace CHAPTER 5 DISTRIBUTED GIT developer developer blessed public public repository ye a integration manager Figure 5 2 Integration manager workflow developer public Dictator and Lieutenants Workflow This is a variant of a multiple repository workflow It s generally used by huge projects with hundreds of collaborators one famous example is the Linux kernel Various integration managers are in charge of certain parts of the repository they re called lieutenants All the lieutenants have one integration manager known as the benevolent dictator The benevolent dictator s repository serves as the reference repository from which all the collaborators need to pull The process works like this see Figure 5 3 1 Regular developers work on their topic branch and rebase their work on top of master The master branch is that of the dictator 2 Lieutenants merge the developers topic branches into their master branch 3 The dictator merges the lieutenants master branches into the dictator s master branch 4 The dictator pushes their master to the reference repository so the other developers can rebase on it This kind of workflow isn t common but can be useful in very big projects or in highly hierarchical environments because it allows the project leader the dictator to delegate much of the work and collect large subsets of
320. pter you should be able to clone a repository see what has happened in the history of the project modify files and contribute changes If the book spontaneously combusts at this point you should already be pretty useful wielding Git in the time it takes you to go pick up another copy Chapter 3 is about the branching model in Git often described as Git s killer feature Here you ll learn what truly sets Git apart from the pack When you re done you may feel the need to spend a quiet moment pondering how you lived before Git branching was part of your life Chapter 4 will cover Git on the server This chapter is for those of you who want to set up Git inside your organization or on your personal server for collaboration You ll also explore various hosted options if you prefer to let someone else handle that for you Chapter 5 will go over in full detail various distributed workflows and how to accomplish them with Git When you re done with this chapter you should be able to work expertly with multiple remote repositories use Git over e mail and deftly juggle numerous remote branches and contributed patches Chapter 6 is about advanced Git commands You ll learn about topics like binary search ing to identify bugs editing history revision selection in detail and a lot more This chapter will round out your knowledge of Git so that you re truly a master Chapter 7 is about configuring your custom Git environment This includes setting up h
321. ptions for the git log pretty Output Option Description of Output AH Commit hash h Abbreviated commit hash AT Tree hash t Abbreviated tree hash P Parent hashes p Abbreviated parent hashes an Author name ae Author e mail ad Author date format respects the date option ar Author date relative cn Committer name ce Committer e mail cd Committer date cr Committer date relative s Subject Note You may be wondering what the difference is between author and committer The author is the per son who originally wrote the work whereas the committer is the person who last applied the work So if you send in a patch to a project and one of the core members applies the patch both of you get credit you as the author and the core member as the committer I ll cover this distinction a bit more in Chapter 5 30 CHAPTER 2 GIT BASICS The oneline and format options are particularly useful with another log option called graph This option adds a nice little ASCII graph showing your branch and merge history in which you can see your copy of the Grit project repository git log pretty format h s graph 2d3acf9 ignore errors from SIGCHLD on trap 5e3ee11 Merge branch master of git github com dustin grit I 420eac9 Added a method for getting the current branch 30e367c timeout code and tests 5a09431 add timeout protection to grit e1193f8 support for heads with slashes in them
322. pulls down all the data for that repository and checks out a working copy of the latest version If you go into the new grit directory you ll see the project files in there ready to be worked on or used If you want to clone the repository into a directory named something other than grit you can specify that as the next command line option git clone git github com schacon grit git mygrit This command does the same thing as the previous one but the target directory is called mygrit Git has a number of different transfer protocols you can use The previous example uses the git protocol but you may also see http s or user server path git which uses the SSH transfer protocol Chapter 4 will introduce all of the available options the server can set up to access your Git repository and the pros and cons of each Recording Changes to the Repository You have a bona fide Git repository and a checkout or working copy of the files for that project You need to make some changes and commit snapshots of those changes into your repository each time the project reaches a state you want to record Remember that each file in your working directory can be in one of two states tracked or untracked Tracked files are files that were in the last snapshot they can be unmodified modi fied or staged Untracked files are everything else any files in your working directory that weren t in your last snapshot and aren t in your staging area When
323. r 1 6 2 rc1 20 g8c5b dirty You can also edit these patch files to add more information for the e mail list that you don t want to show up in the commit message If you add text between the line and the beginning of the patch the lib simplegit rb line then developers can read it but applying the patch excludes it To e mail this to a mailing list you can either paste the file into your e mail program or send it via a command line program Pasting the text often causes formatting issues especially with smarter clients that don t preserve newlines and other whitespace appropriately Luck ily Git provides a tool to help you send properly formatted patches via IMAP which may be easier for you I ll demonstrate how to send a patch via Gmail which happens to be the e mail agent I use you can read detailed instructions for a number of mail programs at the end of the aforementioned Documentation SubmittingPatches file in the Git source code First you need to set up the imap section in your gitconfig file You can set each value separately with a series ofgit config commands or you can add them manually but in the end your config file should look something like this imap folder Gmail Drafts host imaps imap gmail com CHAPTER 5 DISTRIBUTED GIT 129 user user gmail com pass p4sswOrd port 993 sslverify false If your IMAP server doesn t use SSL the last two lines probably aren t necessary and the h
324. r HEAD to where you were before you started or you ll end up in a weird state git bisect reset This is a powerful tool that can help you check hundreds of commits for an introduced bug in minutes In fact if you have a script that will exit 0 if the project is good or non 0 if the project is bad you can fully automate git bisect First you again tell it the scope of the bisect by providing the known bad and good commits You can do this by listing them with the bisect start command if you want listing the known bad commit first and the known good commit second git bisect start HEAD v1 0 git bisect run test error sh Doing so automatically runs test error sh on each checked out commit until Git finds the first broken commit You can also run something like make or make tests or whatever you have that runs automated tests for you CHAPTER 6 GIT TOOLS 165 Submodules It often happens that while working on one project you need to use another project from within it Perhaps it s a library that a third party developed or that you re developing separately and using in multiple parent projects A common issue arises in these scenarios you want to be able to treat the two projects as separate yet still be able to use one from within the other Here s an example Suppose you re developing a web site and creating Atom feeds Instead of writing your own Atom generating code you decide to use a library You re likely to have to either
325. rb index a0a60ae 47c6340 100644 a lib simplegit rb b lib simplegit rb 18 8 418 3 class SimpleGit end end if 0 FILE 27 28 CHAPTER 2 GIT BASICS git SimpleGit new puts git show end No newline at end of file This option displays the same information but with a diff directly following each entry This is very helpful for code review or to quickly browse what happened during a series of commits that a collaborator has added You can also use a series of summarizing options with git log For example if you want to see some abbreviated stats for each commit you can use the stat option git log stat commit ca82a6dff817ec66f44342007202690a93763949 Author Scott Chacon lt schacon gee mail com gt Date Mon Mar 17 21 52 11 2008 0700 changed the version number Rakefile 2 1 files changed 1 insertions 1 deletions commit 085bb3bcb608e1e8451d4b2432f8ecbe6306e7e7 Author Scott Chacon lt schacon gee mail com gt Date Sat Mar 15 16 40 33 2008 0700 removed unnecessary test code lib simplegit rb Bessie 1 files changed 0 insertions 5 deletions commit a11bef06a3f659402fe7563abf99ad00de2209e6 Author Scott Chacon lt schacon gee mail com gt Date Sat Mar 15 10 31 28 2008 0700 first commit README 6 Rakefile 23 tebe ttt ttt lib simplegit rb 25 3 files changed 54 insertions 0 deletions As you can see the
326. re doing the fetch over SSH fetch pack instead runs something like this n ssh x git github com git upload pack schacon simplegit progit git 244 CHAPTER 9 GIT INTERNALS In either case after fetch pack connects upload pack sends back something like this 0088ca82a6dff817ec66F44342007202690a93763949 HEAD Omulti_ack thin pack side band side band 64k ofs delta shallow no progress include tag 003fca82a6dff817ec66F44342007202690a93763949 refs heads master 003e085bb3bcb608e1e8451d4b2432f8ecbe6306e7e7 refs heads topic 0000 This is very similar to what receive pack responds with but the capabilities are different In addition it sends back the HEAD reference so the client knows what to check out if this is a clone At this point the fetch pack process looks at what objects it has and responds with the objects that it needs by sending want and then the SHA it wants It sends all the objects it already has with have and then the SHA At the end of this list it writes done to initiate the upload pack process to begin sending the packfile of the data it needs 0054want ca82a6dff817ec66f44342007202690a93763949 ofs delta 0032have 085bb3bcb608e1e8451d4b2432f8ecbe6306e7e7 0000 0009done That is a very basic case of the transfer protocols In more complex cases the client sup ports multi ack or side band capabilities but this example shows you the basic back and forth used by the smart protocol processes Maintenance a
327. re on when you merged and the second is the commit on the branch that you merged in git show d921970 commit 1c002dd4b536e7479fe34593e72e6c6c1819e53b Author Scott Chacon lt schacon gmail com gt Date Thu Dec 11 14 58 32 2008 0800 added some blame and merge stuff git show d921970 2 commit 35cfb2b795a55793d7cc56a6cc2060b4bb732548 Author Paul Hedderly lt paul git mjr org gt Date Wed Dec 10 22 22 03 2008 0000 Some rdoc changes The other main ancestry specification is the This also refers to the first parent so HEAD and HEAD are equivalent The difference becomes apparent when you specify a number HEAD 2 means the first parent of the first parent or the grandparent it traverses the first parents the number of times you specify For example in the history listed earlier HEAD 3 would be git show HEAD 3 commit 1c3618887afb5fbcbea25b7c013f4e2114448b8d Author Tom Preston Werner tomgmo jombo com Date Fri Nov 7 13 47 59 2008 0500 ignore gem This can also be written HEAD which again is the first parent of the first parent of the first parent git show HEAD commit 1c3618887afb5fbcbea25b7c013f4e2114448b8d Author Tom Preston Werner tomgmo jombo com Date Fri Nov 7 13 47 59 2008 0500 ignore gem You can also combine these syntaxes you can get the second parent of the previous ref erence assuming it was a merge commit by using HEAD 3 2 and so on Commit Ranges
328. re working on an issue with a partner and they pushed up an iss53 branch you might have your own local iss53 branch but the branch on the server would point to the commit at origin iss53 This may be a bit confusing so let s look at an example Let s say you have a Git server on your network at git ourcompany com If you clone from this Git automatically names it origin CHAPTER 3 GIT BRANCHING for you pulls down all its data creates a pointer to where its master branch is and names it origin master locally and you can t move it Git also gives you your own master branch start ing at the same place as origin s master branch so you have something to work from see Figure 3 22 git ourcompany com master git clone schacon git ourcompany com project git My Computer ees Remote Branch Figure 3 22 A Git clone gives you your own master branch and origin master pointing to origin s master branch If you do some work on your local master branch and in the meantime someone else pushes to git ourcompany com and updates its master branch then your histories move for ward differently Also as long as you stay out of contact with your origin server your origin master pointer doesn t move see Figure 3 23 To synchronize your work you runagit fetch origin command This command looks up which server origin is in this case it s git ourcompany com fetches any data from it that you don t yet have and
329. remote modified Hit return to start merge resolution tool opendiff 60 CHAPTER 3 GIT BRANCHING If you want to use a merge tool other than the default Git chose opendiff for me in this case because I ran the command on a Mac you can see all the supported tools listed at the top after merge tool candidates Type the name of the tool you d rather use In Chapter 7 I ll discuss how you can change this default value for your environment After you exit the merge tool Git asks you if the merge was successful If you tell the script that it was it stages the file to mark it as resolved for you Youcanrungit status again to verify that all conflicts have been resolved git status On branch master Changes to be committed use git reset HEAD lt file gt to unstage modified index html If you re happy with that and you verify that everything that had conflicts has been staged you can type git commit to finalize the merge commit The commit message by default looks something like this Merge branch iss53 Conflicts index html It looks like you may be committing a MERGE If this is not correct please remove the file git MERGE HEAD and try again You can modify that message with details about how you resolved the merge if you think it would be helpful to others looking at this merge in the future why you did what you did if it s not obvious Branch Management Now that you
330. rge CHAPTER 5 DISTRIBUTED GIT aiti dil ruby client nat 3 5 Figure 5 22 After a topic branch merge master develop At Figure 5 23 After a topic branch release ruby client of This way when people clone your project s repository they can either check out master to build the latest stable version and keep up to date on that easily or they can check out develop which is the more cutting edge stuff You can also continue this concept having an integrate branch where all the work is merged together Then when the codebase on that branch is stable and passes tests you merge it into a develop branch and when that has proven itself stable for a while you fast forward your master branch Large Merging Workflows The Git project has four long running branches master next and pu proposed updates for new work and maint for maintenance backports When new work is introduced by contribu tors it s collected into topic branches in the maintainer s repository in a manner similar to what I ve described see Figure 5 24 At this point the topics are evaluated to determine whether they re safe and ready for consumption or whether they need more work If they re safe they re merged into next and that branch is pushed up so everyone can try the topics integrated together 137 138 CHAPTER 5 DISTRIBUTED GIT 0 A O O 3 0 Figure 5 24 Managing a complex series
331. rge her work into so that she can push She runs git log to find out git log no merges origin master issue54 commit 738ee872852dfaa9d6634e0dea7a324040193016 Author John Smith lt jsmith example com gt Date Fri May 29 16 01 27 2009 0700 removed invalid default value Now Jessica can merge her topic work into her master branch merge John s work origin master into her master branch and then push back to the server again First she switches back to her master branch to integrate all this work git checkout master Switched to branch master Your branch is behind origin master by 2 commits and can be fast forwarded She can merge either origin master or issue54 first they re both upstream so the order doesn t matter The end snapshot should be identical no matter which order she chooses only the history will be slightly different She chooses to merge in issue 4 first git merge issue54 Updating fbff5bc 4af4298 Fast forward README 14 lib simplegit rb 6 2 files changed 6 insertions 1 deletions No problems occur as you can see it was a simple fast forward Now Jessica merges in John s work origin master CHAPTER 5 DISTRIBUTED GIT git merge origin master Auto merging lib simplegit rb Merge made by recursive lib simplegit rb 2 1 files changed 1 insertions 1 deletions Everything merges cleanly and Jessica s history looks like Figure 5 9 master origi
332. rom refA or refB but not from refC you can type one of these git log refA refB refC git log refA refB not refC This makes for a very powerful revision query system that should help you figure out what is in your branches Triple Dot The last major range selection syntax is the triple dot syntax which specifies all the commits that are reachable by either of two references but not by both of them Look back at the exam ple commit history in Figure 6 1 If you want to see what is in master or experiment but not any common references you can run git log master experiment F E D C Again this gives you normal log output but shows you only the commit information for those four commits appearing in the traditional commit date ordering A common switch to use with the log command in this case is left right which shows you which side of the range each commit is in This helps make the data more useful git log left right master experiment lt F E gt D gt C With these tools you can much more easily let Git know what commit or commits you want to inspect 150 CHAPTER 6 GIT TOOLS Interactive Staging Git comes with a couple of scripts that make some command line tasks easier Here you ll look at a few interactive commands that can help you easily craft your commits to include only certain combinations and parts of files These tools are very helpful if you modify a bunch of files and then decide
333. rsonal public key If your public key isn t on the server you ll have to copy it there sudo H u git gitosis init tmp id dsa pub Initialized empty Git repository in opt git gitosis admin git Reinitialized existing Git repository in opt git gitosis admin git This lets the user with that key modify the main Git repository that controls the Gitosis setup Next you have to manually set the execute bit on the post update script for your new control repository sudo chmod 755 opt git gitosis admin git hooks post update You re ready to roll If you re set up correctly you can try to SSH into your server as the user for which you added the public key to initialize Gitosis You should see something like this ssh git gitserver PTY allocation request failed on channel O fatal unrecognized command gitosis serve schacongquaternion Connection to gitserver closed CHAPTER 4 GIT ON THE SERVER 93 That means Gitosis recognized you but shut you out because you re not trying to do any Git commands So do an actual Git command and clone the Gitosis control repository on your local computer git clone git gitserver gitosis admin git Now you have a directory named gitosis admin which has two major parts cd gitosis admin find gitosis conf keydir keydir scott pub The gitosis conf file is the control file you use to specify users repositories and permis sions The keydir directory is where you store the pu
334. rstand the way Git does branching you need to take a step back and examine how Git stores its data As you may remember from Chapter 1 Git doesn t store data as a series of changesets or deltas but instead as a series of snapshots When you commit in Git Git stores a commit object that contains a pointer to the snap shot of the content you staged the author and message metadata and zero or more pointers to the commit or commits that were the direct parents of this commit zero parents for the first commit one parent for a normal commit and multiple parents for a commit that results from a merge of two or more branches To visualize this let s assume that you have a directory containing three files and you stage them all and commit Staging the files checksums each one the SHA 1 hash I mentioned in Chapter 1 stores that version of the file in the Git repository Git refers to them as blobs and adds that checksum to the staging area git add README test rb LICENSE2 git commit m initial commit of my project When you create the commit by running git commit Git checksums each subdirectory in this case just the root project directory and stores those tree objects in the Git repository Git then creates a commit object that has the metadata and a pointer to the root project tree so it can re create that snapshot when needed 47 48 CHAPTER 3 GIT BRANCHING Your Git repository now contains five objects one blob for
335. s git log contrib not master commit 5b6235bd297351589efc4d73316f0a68d484f118 Author Scott Chacon lt schacon gmail com gt Date Fri Oct 24 09 53 59 2008 0700 seeing if this helps the gem commit 7482e0d16d04bea79d0dba8988cc78df655f16a0 Author Scott Chacon lt schacon gmail com gt Date Mon Oct 22 19 38 36 2008 0700 updated the gemspec to hopefully work better To see what changes each commit introduces remember that you can pass the p option to git log and it will append the diff introduced to each commit To see a full diff of what would happen if you were to merge this topic branch with another branch you may have to use a weird trick to get the correct results You may think to run this git diff master This command gives you a diff but it may be misleading If your master branch has moved forward since you created the topic branch from it then you ll get seemingly strange results This happens because Git directly compares the snapshots of the last commit of the topic branch you re on and the snapshot of the last commit on the master branch For example if you ve added a line in a file on the master branch a direct comparison of the snapshots will look like the topic branch is going to remove that line If master is a direct ancestor of your topic branch this isn t a problem but if the two his tories have diverged the diff will look like you re adding all the new stuff in your topic branch and removing everyt
336. s generally a good idea to do this in a testing branch and then hard reset your master branch after you ve determined the outcome is what you really want To run filter branch on all your branches you can pass all to the command Making a Subdirectory the New Root Suppose you ve done an import from another source control system and have subdirectories that make no sense trunk tags and so on If you want to make the trunk subdirectory be the new project root for every commit filter branch can help you do that too git filter branch subdirectory filter trunk HEAD Rewrite 856f0bf61e41a27326cdae8f09fe7084d679f596f 12 12 Ref refs heads master was rewritten Now your new project root is what was in the trunk subdirectory each time Git will also automatically remove commits that didn t affect the subdirectory Changing E mail Addresses Globally Another common case is that you forgot to run git config to set your name and e mail address before you started working or perhaps you want to open source a project at work and change all your work e mail addresses to your personal address In any case you can change e mail addresses in multiple commits in a batch with filter branch as well You need to be careful to change only the e mail addresses that are yours so you use commit filter git filter branch commit filter if GIT AUTHOR EMAIL schacon localhost then GIT AUTHOR NAME Scott Chacon GIT AUTHOR EMAIL scha
337. s often helpful especially when you re dealing with very large or complex projects Topic Branches Topic branches however are useful in projects of any size A topic branch is a short lived branch that you create and use for a single particular feature or related work This is some thing you ve likely never done with a VCS before because it s generally too expensive to create and merge branches But in Git it s common to create work on merge and delete branches several times a day You saw this in the last section with the 15553 and hotfix branches you created You did a few commits on them and deleted them directly after merging them into your main branch This technique allows you to context switch quickly and completely because your work is separated into silos where all the changes in that branch have to do with that topic it s easier to see what has happened during code review and such You can keep the changes there for minutes days or months and merge them in when they re ready regardless of the order in which they were created or worked on Consider an example of doing some work on master branching off for an issue 15591 working on it for a bit branching off the second branch to try another way of handling the same thing 1ss91v2 going back to your master branch and working there for a while and then branching off there to do some work that you re not sure is a good idea dumbidea branch Your commit history looks some
338. s to share their code and you re familiar with basic Git commands in a local workflow you ll look at how to utilize some of the distributed workflows that Git affords you In this chapter you ll see how to work with Git in a distributed environment as a contribu tor and an integrator That is you ll learn how to contribute code successfully to a project and make it as easy on you and the project maintainer as possible and also how to maintain a project successfully with a number of developers contributing Distributed Workflows Unlike Centralized Version Control Systems CVCSs the distributed nature of Git allows you to be far more flexible in how developers collaborate on projects In centralized systems every developer is a node working more or less equally on a central hub In Git however every developer is potentially both a node and a hub that is every developer can both contribute code to other repositories and maintain a public repository on which others can base their work and which they can contribute to This opens a vast range of workflow possibilities for your project and or your team so I ll cover a few common paradigms that take advantage of this flexibility I ll go over the strengths and possible weaknesses of each design you can choose a single one to use or you can mix and match features from each Centralized Workflow In centralized systems there is generally a single collaboration model the centralized work
339. ser so you can push to it This way projects don t have to worry about adding users as collaborators to give them push access People can fork a project and push to it and the main project maintainer can pull in those changes by adding them as remotes and merging in their work To fork a project visit the project page in this case mojombo chronic and click the fork button in the header see Figure 4 14 e h b a schacon account profile log out t githuD Browse Guides Advanced E3 182 stafftools dashboard gists Source Commits Network 36 Downloads 0 Wiki 1 Graphs master all branches all tags venero a d watch amp download 4130 38 3 Description Chr PE natural language date parser Homepage http chronic rubyforge org Public Clone URL git github com mojombo chronic git if Added tests for RepeaterMinute commit 180e44763ac36d9ee4cdc350f 90900f1517a05b73 tree Gb88Sfcde0674d685796a209270ef d9f579f 28516a Brian Browning author parent a9ad71d4460c589e92883c06beaeS99b4 f Bf d df November 13 2008 Figure 4 14 Get a writable copy of any repository by clicking the fork button After a few seconds you re taken to your new project page which indicates that this proj ect is a fork of another one see Figure 4 15 CHAPTER 4 GIT ON THE SERVER 105 schacon chronic Cedit C unwatch Fork of mojombo chronic Description Chronic is a pure Ruby natural langua
340. sert information The commit msg hook takes one parameter which again is the path to a temporary file that contains the current commit message If this script exits non zero Git aborts the commit process so you can use it to validate your project state or commit message before allowing a commit to go through In the last section of this chapter I ll demonstrate using this hook to check that your commit message is conformant to a required pattern After the entire commit process is completed the post commit hook runs It doesn t take any parameters but you can easily get the last commit by running git log 1 HEAD Generally this script is used for notification or something similar The committing workflow client side scripts can be used in just about any workflow They re often used to enforce certain policies although it s important to note that these scripts aren t transferred during a clone You can enforce policy on the server side to reject pushes of commits that don t conform to some policy but it s entirely up to the developer to use these scripts on the client side So these are scripts to help developers and they must be set up and maintained by them although they can be overridden or modified by them at any time E mail Workflow Hooks You can set up three client side hooks for an e mail based workflow They re all invoked by the git am command so if you aren t using that command in your workflow you can safely skip to the
341. set Git colors its output if the output goes to a terminal Other possible settings are false which never colors the output and always which sets colors all the time even if you re redirecting Git commands to a file or piping them to another command This setting was added in Git version 1 5 5 if you have an older version you ll have to specify all the color settings individually You ll rarely want color ui always In most scenarios if you want color codes in your redirected output you can instead pass a color flag to the Git command to force it to use color codes The color ui true setting is almost always what you ll want to use color If you want to be more specific about which commands are colored and how or you have an older version Git provides verb specific coloring settings Each of these can be set to true false or always CHAPTER 7 CUSTOMIZING GIT 179 color branch color diff color interactive color status In addition each of these has subsettings you can use to set specific colors for parts of the output if you want to override each color For example to set the meta information in your diff output to blue foreground black background and bold text you can run git config global color diff meta blue black bold You can set the color to any of the following values normal black red green yellow blue magenta cyan or white If you want an attribute like bold in the previous example you can c
342. st unless a request has been made pursuant to Section 4 a keep intact all copyright notices for the Work and provide reasonable to the medium or means You are utilizing i the name of the Original Author or pseudonym if applicable if supplied and or if the Original Author and or Licensor designate another party or parties e g a sponsor institute publishing entity journal for attribution Attribution Parties in Licensor s copyright notice terms of service or by other reasonable means the name of such party or parties ii the title of the Work if supplied iii to the extent reasonably practicable the URI if any that Licensor specifies to be associated with the Work unless such URI does not refer to the copyright notice or licensing information for the Work and iv consistent with Section 3 b in the case of an Adaptation a credit identifying the use of the Work in the Adaptation e g French translation of the Work by Original Author or Screenplay based on original Work by Original Author The credit required by this Section 4 d may be implemented in any reasonable manner provided however that in the case of a Adaptation or Collection at a minimum such credit will appear if a credit for all contributing authors of the Adaptation or Collection appears then as part of these credits and in a manner at least as prominent as the credits for the other contributing authors For the avoidance of doubt You may only use t
343. ster Existing Git Repo cd existing_git_repo git remote add origin git github com testinguser iphone_project git git push origin master Importing a SVN Repo Click here When you re done Continue Figure 4 7 Instructions for a new repository These instructions are similar to what you ve already gone over To initialize a project if it isn t already a Git project you use git init git add git commit m initial commit When you have a Git repository locally add GitHub as a remote and push up your master branch git remote add origin git github com testinguser iphone_project git git push origin master Now your project is hosted on GitHub and you can give the URL to anyone you want to share your project with In this case it s http github com testinguser iphone project You can also see from the header on each of your project s pages that you have two Git URLs see Figure 4 8 CHAPTER 4 GIT ON THE SERVER 101 testinguser iphone project Ce edit C unwatch Description iphone project for our mobile group adit Homepage Click to edit edit Public Clone URL git github com testinguseriphone_project git is Your Clone URL gitigithub com testinguser iphone project git E Figure 4 8 Project header with a public URL and a private URL The Public Clone URL is a public read only Git URL over which anyone can clone the project Feel free to give out that URL and post it on your web site
344. submodule you must be careful or Git will get angry at you Assume that you have the rack files in a subdirectory of your project and you want to switch it to a submodule If you delete the subdirectory and then run submodule add Git yells at you rm Rf rack git submodule add git github com schacon rack git rack rack already exists in the index You have to unstage the rack directory first Then you can add the submodule git rm r rack git submodule add git github com schacon rack git rack Initialized empty Git repository in opt testsub rack git remote Counting objects 3184 done remote Compressing objects 100 1465 1465 done remote Total 3184 delta 1952 reused 2770 delta 1675 Receiving objects 100 3184 3184 677 42 KiB 88 KiB s done Resolving deltas 100 1952 1952 done Now suppose you did that in a branch If you try to switch back to a branch where those files are still in the actual tree rather than a submodule you get this error git checkout master error Untracked working tree file rack AUTHORS would be overwritten by merge You have to move the rack submodule directory out of the way before you can switch to a branch that doesn t have it mv rack tmp git checkout master Switched to branch master Is README rack CHAPTER 6 GIT TOOLS 171 Then when you switch back you get an empty rack directory You can either run git submodule update to reclone or you can
345. symbolic reference I mean that unlike a normal reference it doesn t generally contain a SHA 1 value but rather a pointer to another reference If you look at the file you ll normally see something like this cat git HEAD ref refs heads master Ifyou run git checkout test Git updates the file to look like this cat git HEAD ref refs heads test When you run git commit it creates the commit object specifying the parent of that com mit object to be whatever SHA 1 value the reference in HEAD points to You can also manually edit this file but again a safer command exists to do so symbolic ref You can read the value of your HEAD via this command git symbolic ref HEAD refs heads master 234 CHAPTER 9 GIT INTERNALS You can also set the value of HEAD git symbolic ref HEAD refs heads test cat git HEAD ref refs heads test You can t set a symbolic reference outside of the refs style git symbolic ref HEAD test fatal Refusing to point HEAD outside of refs Tags You ve just gone over Git s three main object types but there is a fourth The tag object is very much like a commit object it contains a tagger a date a message and a pointer The main difference is that a tag object points to a commit rather than a tree It s like a branch reference but it never moves it always points to the same commit but gives it a friendlier name As discussed in Chapter 2 there are two types of tags annotated and li
346. t start on startup stop on shutdown exec usr bin git daemon user git group git reuseaddr V base path opt git opt git respawn For security reasons you re strongly encouraged to have this daemon run as a user with read only permissions to the repositories you can easily do this by creating a new user git ro and running the daemon as that user For the sake of simplicity run it as the same git user that Gitosis is running as 96 CHAPTER 4 GIT ON THE SERVER When you restart your machine your Git daemon starts automatically and respawns if it goes down To get it running without having to reboot you can run this initctl start local git daemon On other systems you may want to use xinetd a script in your sysvinit system or some thing else as long as you get that command daemonized and watched somehow Next you have to tell your Gitosis server which repositories to allow unauthenticated Git server based access to If you add a section for each repository you can specify the ones from which you want your Git daemon to allow reading If you want to allow Git protocol access for your iphone project you add this to the end of the gitosis conf file repo iphone project daemon yes When that is committed and pushed up your running daemon should start serving requests for the project to anyone who has access to port 9418 on your server If you decide not to use Gitosis but you want to set up a Git
347. t and more important for me introduced me to the tool and taught me how to use it back in the pre 1 0 days There is probably no way I would be doing all this if he had not brought Git to my attention and introduced it to the environment in which we both worked Further thanks go to Chris Wanstrath Tom Preston Werner and PJ Hyett for inviting me to join them in working on GitHub very early on allowing me to spend basically all my time thinking about and working on Git related projects It s difficult to imagine a better group of people to work with or a better job to have Last I want to thank my wife Jessica who kept me continually working at this Writing a book of this scope is a heck of a process and when I stalled out from time to time she made sure I got back on track Thanks Magoo xix Introduction Yu about to spend several hours of your life reading about Git Let s take a minute to explain what we have in store for you Here is a quick summary of this book s nine chapters In Chapter 1 you ll cover Version Control Systems VCSs and Git basics no technical stuff just what Git is why it came about in a land full of VCSs what sets it apart and why so many people are using it Then you ll learn how to download Git and set it up for the first time if you don t already have it on your system In Chapter 2 you ll go over basic Git usage how to use Git in the 80 of cases you ll encounter most often After reading this cha
348. t b serverfix origin serverfix Branch serverfix set up to track remote branch refs remotes origin serverfix Switched to a new branch serverfix CHAPTER 3 GIT BRANCHING 69 This gives you a local branch that you can work on that starts where origin serverfix is Tracking Branches Checking out a local branch from a remote branch automatically creates what is called a track ing branch Tracking branches are local branches that have a direct relationship to a remote branch If you re on a tracking branch and type git push Git automatically knows which server and branch to push to Also running git pull while on one of these branches fetches all the remote references and then automatically merges in the corresponding remote branch When you clone a repository it generally automatically creates a master branch that tracks origin master That s why git push and git pull work out of the box with no other argu ments However you can set up other tracking branches if you wish ones that don t track branches on origin and don t track the master branch The simple case is the example you just saw running git checkout b branch remotename branch If you have Git version 1 6 2 or later you can also use the track shorthand git checkout track origin serverfix Branch serverfix set up to track remote branch refs remotes origin serverfix Switched to a new branch serverfix To set up a local branch with a different name than the re
349. t out If this is better suited to your data check the fast import man page for details about how to provide your data in this manner CHAPTER 8 GIT AND OTHER SYSTEMS 219 The format for listing the new file contents or specifying a modified file with the new con tents is as follows M 644 inline path to file data size file contents Here 644 is the mode if you have executable files you need to detect and specify 755 instead and inline says you ll list the contents immediately after this line Your inline data method looks like this def inline data file code M mode 644 content File read file puts code mode inline file export_data content end You reuse the export_data method you defined earlier because it s the same as the way you specified your commit message data The last thing you need to do is to return the current mark so it can be passed to the next iteration return mark That s it If you run this script you ll get content that looks something like this you can download the full script from http github com progit book examples ruby import rb opt import from commit refs heads master mark 1 committer Scott Chacon lt schacon geemail com gt 1230883200 0700 data 29 imported from back 2009 01 O2deleteall M 644 inline file rb data 12 version two commit refs heads master mark 2 committer Scott Chacon schaconggeemail com 1231056000 0700 data 29 imported
350. t output loop through each of those commit SHAs grab the message for it and test that message against a regular expression that looks for a pattern You have to figure out how to get the commit message from each of these commits to test To get the raw commit data you can use another plumbing command called git cat file I ll go over all these plumbing commands in detail in Chapter 9 but for now here s what that command gives you git cat file commit ca82a6 tree cfda3bf379e4f8dba8717dee55aab78aef7f4daf parent 085bb3bcb608e1e8451d4b2432f8ecbe6306e7e7 author Scott Chacon lt schacon gmail com gt 1205815931 0700 committer Scott Chacon schaconggmail com 1240030591 0700 changed the version number A simple way to get the commit message from a commit when you have the SHA 1 value is to go to the first blank line and take everything after that You can do so with the sed command on Unix systems git cat file commit ca82a6 sed 1 d changed the version number You can use that incantation to grab the commit message from each commit that is trying to be pushed and exit if you see anything that doesn t match To exit the script and reject the push exit non zero The whole method looks like this regex N ref d enforced custom commit message format def check message format missed revs git rev list oldrev newrev split n CHAPTER 7 CUSTOMIZING GIT 195 missed revs each do rev message
351. t s tested merge the hotfix branch and push to production 4 Switch back to your original story and continue working Basic Branching First let s say you re working on your project and have a couple of commits already see Figure 3 10 Figure 3 10 A short and simple commit history You ve decided that you re going to work on issue 53 in whatever issue tracking system your company uses To be clear Git isn t tied into any particular issue tracking system but because 53 is a focused topic that you want to work on you ll create a new branch in which to work To create a branch and switch to it at the same time you can run the git checkout com mand with the b switch git checkout b iss53 Switched to a new branch iss53 This is shorthand for git branch iss53 git checkout iss53 54 CHAPTER 3 GIT BRANCHING Figure 3 11 illustrates the result master o c iss53 H E p Figure 3 11 Creating a new branch pointer You work on your web site and do some commits Doing so moves the iss53 branch for ward because you have it checked out that is your HEAD is pointing to it see Figure 3 12 vim index html git commit a m added a new footer issue 53 Figure 3 12 The iss53 branch has moved forward with your work Now you get the call that there is an issue with the web site and you need to fix it imme diately With Git you don t have to deploy your fix alon
352. t shows you that a couple of lines are staged and a couple are unstaged You ve partially staged this file At this point you can exit the interactive adding script and run git commit to commit the partially staged files Finally you don t need to be in interactive add mode to do the partial file staging you can start the same script by using git add porgit add patch on the command line Stashing Often when you ve been working on part of your project things are in a messy state and you want to switch branches for a bit to work on something else The problem is you don t want to do a commit of half done work just so you can get back to this point later The answer to this issue is the git stash command Stashing takes the dirty state of your working directory that is your modified tracked files and staged changes and saves it on a stack of unfinished changes that you can reapply at any time 154 CHAPTER 6 GIT TOOLS Stashing Your Work To demonstrate you ll go into your project and start working on a couple of files and possibly stage one ofthe changes If you run git status you can see your dirty state git status On branch master Changes to be committed use git reset HEAD lt file gt to unstage modified index html Changed but not updated use git add file to update what will be committed modified lib simplegit rb He He ie ito ito it HE HE Now you want to switch branches bu
353. t you don t want to commit what you ve been work ing on yet so you ll stash the changes To push a new stash onto your stack run git stash git stash Saved working directory and index state V WIP on master 049d078 added the index file HEAD is now at 0494078 added the index file To restore them type git stash apply Your working directory is clean git status On branch master nothing to commit working directory clean At this point you can easily switch branches and do work elsewhere your changes are stored on your stack To see which stashes you ve stored you can use git stash list git stash list stash8 0 WIP on master 049d078 added the index file stash 1 WIP on master c264051 Revert added file size stash 2 WIP on master 21d80a5 added number to log In this case two stashes were done previously so you have access to three different stashed works You can reapply the one you just stashed by using the command shown in the help output of the original stash command git stash apply If you want to apply one of the older stashes you can specify it by naming it like this git stash apply stash 2 If you don t specify a stash Git assumes the most recent stash and tries to apply it CHAPTER 6 GIT TOOLS 155 git stash apply On branch master Changed but not updated use git add lt file gt to update what will be committed modified index html modified lib simplegit rb
354. te server info GET objects info packs P pack 816a9b2334da9953e530f27bcac22082a9f5b835 pack There is only one packfile on the server so your object is obviously in there but you ll check the index file to make sure This is also useful if you have multiple packfiles on the server so you can see which packfile contains the object you need gt GET objects pack pack 816a9b2334da9953e530f27bcac22082a9f5b835 idx 4k of binary data 242 CHAPTER 9 GIT INTERNALS Now that you have the packfile index you can see if your object is in it because the index lists the SHAs of the objects contained in the packfile and the offsets to those objects Your object is there so go ahead and get the whole packfile gt GET objects pack pack 816a9b2334da9953e530f27bcac22082a9f5b835 pack 13k of binary data You have your tree object so you continue walking your commits They re all also within the packfile you just downloaded so you don t have to do any more requests to your server Git checks out a working copy of the master branch that was pointed to by the HEAD reference you downloaded at the beginning The entire output of this process looks like this git clone http github com schacon simplegit progit git Initialized empty Git repository in private tmp simplegit progit git got ca82a6dff817ec66f44342007202690a93763949 walk ca82a6dff817ec66f44342007202690a93763949 got 085bb3bcb608e1e8451d4b2432f8ecbe6306e7e7 Getting alter
355. text format that can be compared via the normal diff CHAPTER 7 CUSTOMIZING GIT 185 Because this is a pretty cool and not widely known feature I ll go over a few examples First you ll use this technique to solve one of the most annoying problems known to human ity version controlling Word documents Everyone knows that Word is the most horrific editor around but oddly everyone uses it If you want to version control Word documents you can stick them in a Git repository and commit every once in a while but what good does that do If you run git diff normally you only see something like this git diff diff git a chapter1 doc b chapter1 doc index 88839c4 4afcb7c 100644 Binary files a chapteri doc and b chapteri doc differ You can t directly compare two versions unless you check them out and scan them manu ally right It turns out you can do this fairly well using Git attributes Put the following line in your gitattributes file doc diff word This tells Git that any file that matches this pattern doc should use the word filter when you try to view a diff that contains changes What is the word filter You have to set it up Here you ll configure Git to use the strings program to convert Word documents into readable text files which it will then diff properly git config diff word textconv strings Now Git knows that if it tries to do a diff between two snapshots and any of the files end in doc it shou
356. that you want those changes to be in several focused commits rather than one big messy commit This way you can make sure your commits are logically separate changesets and can be easily reviewed by the developers working with you If you run git add with the i or interactive option Git goes into an interactive shell mode displaying something like this git add i staged unstaged path 1 unchanged 0 1 TODO 2 unchanged 1 1 index html 3 unchanged 5 1 lib simplegit rb Commands 1 status 2 update 3 revert 4 add untracked 5 patch 6 diff 7 quit 8 help What now You can see that this command shows you a much different view of your staging area basically the same information you get with git status but a bit more succinct and informative It lists the changes you ve staged on the left and unstaged changes on the right After this comes a Commands section Here you can do a number of things including stag ing files unstaging files staging parts of files adding untracked files and seeing diffs of what has been staged Staging and Unstaging Files If you type 2 or uat the What now prompt the script prompts you for which files you want to stage What now 2 staged unstaged path 1 unchanged 0 1 TODO 2 unchanged 1 1 index html 3 unchanged 5 1 lib simplegit rb Update To stage the TODO and index html files you can type the numbers Update 1 2 staged unstaged path dt unchanged
357. the contents of each of your three files one tree that lists the contents of the directory and specifies which file names are stored as which blobs and one commit with the pointer to that root tree and all the commit metadata Conceptually the data in your Git repository looks something like Figure 3 1 5bld3 Testing Library This library is used to test Ruby projects 92ec2 911e7 blob 5b1d3 README gt The MIT License blob 911e7 Copyright c year copyright Permission is hereby granted LIUM initial commit of my sari ol 5e te a cba0a require rubygess require pp module Test module Tester Figure 3 1 Single commit repository data If you make some changes and commit again the next commit stores a pointer to the commit that came immediately before it After two more commits your history might look something like Figure 3 2 A branch in Git is simply a lightweight movable pointer to one of these commits The default branch name in Git is master As you initially make commits you re given a master branch that points to the last commit you made Every time you commit it moves forward automatically What happens if you create a new branch Well doing so creates a new pointer for you to move around Let s say you create a new branch called testing You do this with the git branch command git branch testing CHAPTER 3 GIT BRANCHING 49 98c
358. thing like Figure 3 20 C12 C11 4G G master C10 5 G C C3 2 a A 2 a o C co Figure 3 20 Your commit history with multiple topic branches 64 CHAPTER 3 GIT BRANCHING Now let s say you decide you like the second solution to your issue best iss91v2 You showed the dumbidea branch to your coworkers and it turns out to be genius You can throw away the original iss91 branch losing commits C5 and C6 and merge in the other two Your history then looks like Figure 3 21 master a C12 8 C10 ri c 4 e 2 C C Figure 3 21 Your history after merging in dumbidea and iss91v2 It s important to remember when you re doing all this that these branches are completely local When you re branching and merging everything is being done only in your Git reposi tory no server communication is happening Remote Branches Remote branches are references to the state of branches on your remote repositories They re local branches that you can t move they re moved automatically whenever you do any net work communication Remote branches act as bookmarks to remind you where the branches on your remote repositories were the last time you connected to them They take the form remote branch For instance if you wanted to see what the master branch on your origin remote looked like as of the last time you communicated with it you would check the origin master branch If you we
359. this technology and feel more comfortable using Git in more advanced ways APPENDIX Creative Commons Legal Code Attribution NonCommercial ShareAlike 3 0 Unported Reprinted from http creativecommons org licenses by nc sa 3 0 legalcode CREATIVE COMMONS CORPORATION IS NOT A LAW FIRM AND DOES NOT PROVIDE LEGAL SERVICES DISTRIBUTION OF THIS LICENSE DOES NOT CREATE AN ATTORNEY CLIENT RELATIONSHIP CREATIVE COMMONS PROVIDES THIS INFORMATION ON AN AS IS BASIS CREATIVE COMMONS MAKES NO WARRANTIES REGARDING THE INFORMATION PROVIDED AND DISCLAIMS LIABILITY FOR DAMAGES RESULTING FROM ITS USE License THE WORK AS DEFINED BELOW IS PROVIDED UNDER THE TERMS OF THIS CREATIVE COMMONS PUBLIC LICENSE CCPL OR LICENSE THE WORK IS PROTECTED BY COPY RIGHT AND OR OTHER APPLICABLE LAW ANY USE OF THE WORK OTHER THAN AS AUTHORIZED UNDER THIS LICENSE OR COPYRIGHT LAW IS PROHIBITED BY EXERCISING ANY RIGHTS TO THE WORK PROVIDED HERE YOU ACCEPT AND AGREE TO BE BOUND BY THE TERMS OF THIS LICENSE TO THE EXTENT THIS LICENSE MAY BE CONSIDERED TO BE A CONTRACT THE LICENSOR GRANTS YOU THE RIGHTS CONTAINED HERE IN CONSIDERATION OF YOUR ACCEPTANCE OF SUCH TERMS AND CONDITIONS 1 Definitions a Adaptation means a work based upon the Work or upon the Work and other pre existing works such as a translation adaptation derivative work arrangement of music or other alterations of a literary or artistic work or phonogr
360. ting objects 50 done Compressing objects 100 38 38 done Writing objects 100 44 44 4 56 KiB done Total 44 delta 18 reused 8 delta 1 To git github com schacon simplegit git new tag V1 5 gt v1 5 If you have a lot of tags that you want to push up at once you can also use the tags option to the git push command This transfers to the remote server all of your tags that aren t already there git push origin tags Counting objects 50 done Compressing objects 100 38 38 done Writing objects 100 44 44 4 56 KiB done Total 44 delta 18 reused 8 delta 1 To git github com schacon simplegit git new tag v0 1 gt vO 1 new tag v1 2 gt v1 2 new tag v1 4 gt V1 4 new tag v1 4 lw gt v1 4 lw new tag v1 5 gt v1 5 Now when someone else clones or pulls from your repository they will get all your tags as well Tips and Tricks Before I finish this chapter on basic Git a few little tips and tricks may make your Git experi ence a bit simpler easier or more familiar Many people use Git without using any of these tips and I won t refer to them or assume you ve used them later in the book but you should probably know how to do them Auto Completion If you use the Bash shell Git comes with a nice auto completion script you can enable Download the Git source code and look in the contrib completion directory there should be a file called git completion bash
361. to your projects you ll want to move past the HTTP protocol and start using the Git protocol The main reason is speed The Git protocol is far more efficient and thus faster than the HTTP protocol so using it will save your users time Again this is for unauthenticated read only access If you re running this on a server out side your firewall it should only be used for projects that are publicly visible to the world If the server you re running it on is inside your firewall you might use it for projects that a large number of people or computers continuous integration or build servers have read only access to when you don t want to have to add an SSH key for each In any case the Git protocol is relatively easy to set up Basically you need to run this command in a daemonized manner git daemon reuseaddr base path opt git opt git reuseaddr allows the server to restart without waiting for old connections to time out the base path option allows people to clone projects without specifying the entire path and the path at the end tells the Git daemon where to look for repositories to export If you re running a firewall you also need to punch a hole in it at port 9418 on the box you re setting this up on You can daemonize this process a number of ways depending on the operating system you re running On an Ubuntu machine you use an Upstart script So in the following file etc event d local git daemon you put this scrip
362. tribution If you re on Fedora you can use yum yum install git core Or if you re on a Debian based distribution like Ubuntu try apt get apt get install git core Installing on Mac There are two easy ways to install Git on a Mac The easiest is to use the graphical Git installer which you can download from the Google Code page see Figure 1 7 http code google com p git osx installer instal Cit instaler 1 6 0 5 Custom Install on Scotts Computer Package hare Action M or install Amend PATH and MANPATH for git install Soace eases 10 4 ME Remaining 14808 GoBack Continue Figure 1 7 Git Mac OS X installer The other major way is to install Git via MacPorts http www macports org If you have MacPorts installed install Git via sudo port install git core svn doc bash_completion gitweb You don t have to add all the extras but you ll probably want to include svn in case you ever have to use Git with Subversion repositories see Chapter 8 CHAPTER 1 GETTING STARTED 11 Installing on Windows Installing Git on Windows is very easy The msysGit project has one of the easier installation procedures Simply download the installer exe file from the Google Code page and run it http code google com p msysgit After it s installed you have both a command line version including an SSH client that will come in handy later and the standard GUI First Time Git Setup Now
363. true if path begins with access path this ensures that access path is not just in one of the allowed paths but each accessed path begins with an allowed path Now your users can t push any commits with badly formed messages or with modified files outside of their designated paths Enforcing Fast Forward Only Pushes The only thing left is to enforce fast forward only pushes In Git versions 1 6 or newer you can set the receive denyDeletes and receive denyNonFastForwards settings But enforcing this with a hook will work in older versions of Git and you can modify it to do so only for certain users or whatever else you come up with later The logic for checking this is to see if any commits are reachable from the older revision that aren t reachable from the newer one If there are none then it was a fast forward push otherwise you deny it enforces fast forward only pushes def check_fast_forward missed refs git rev list newrev oldrev missed ref count missed _refs split n size if missed ref count gt 0 puts POLICY Cannot push a non fast forward reference exit 1 end end check_fast_forward Everything is set up If yourun chmod u x git hooks update which is the file into which you should have put all this code and then try to push a non fast forwarded reference you get something like this git push f origin master Counting objects 5 done 198 CHAPTER 7 CUSTOMIZING GIT Compressing ob
364. tty oneline ab1afef80fac8e34258ff41fc1b867c702daa24b modified repo a bit 484a59275031909e19aadb7c92262719cfcdf19a added repo rb 1a410efbd13591db07496601ebc7a059dd55cfe9 third commit cac0cab538b970a37ea1e769cbbde608743bc96d second commit fdf4fc3344e67ab0681836878b6c4951e3b15f3d first commit Now move the master branch back to the middle commit git reset hard 1a410efbd13591db07496601ebc7a059dd55cfe9 HEAD is now at 1a410ef third commit git log pretty oneline 1a410efbd13591db07496601ebc7a059dd55cfe9 third commit cac0cab538b970a37ea1e769cbbde608743bc96d second commit fdf4fc3344e67ab068f836878b6c4951e3b15f3d first commit You ve effectively lost the top two commits you have no branch from which those com mits are reachable You need to find the latest commit SHA and then add a branch that points to it The trick is finding that latest commit SHA it s not like you ve memorized it right 246 CHAPTER 9 GIT INTERNALS Often the quickest way is to use a tool called git reflog As you re working Git silently records what your HEAD is every time you change it Each time you commit or change branches the reflog is updated The reflog is also updated by the git update ref command which is another reason to use it instead of just writing the SHA value to your ref files as you learned in the Git References section of this chapter You can see where you ve been at any time by running git reflog git reflog 1a410ef HEAD O 1a410e
365. u change pick to edit on more lines you can repeat these steps for each commit you change to edit Each time Git will stop let you amend the commit and continue when you re finished Reordering Commits You can also use interactive rebases to reorder or remove commits entirely If you want to remove the added cat file commit and change the order in which the other two commits are introduced you can change the rebase script from this CHAPTER 6 GIT TOOLS 159 pick f7f3f6d changed my name a bit pick 310154e updated README formatting and added blame pick a5f4a0d added cat file to this pick 310154e updated README formatting and added blame pick f7f3f6d changed my name a bit When you save and exit the editor Git rewinds your branch to the parent of these com mits applies 310154e and then f7f3f6d and then stops You effectively change the order of those commits and remove the cat file commit completely Squashing a Commit It s also possible to take a series of commits and squash them down into a single commit with the interactive rebasing tool The script puts helpful instructions in the rebase message Commands p pick use commit e edit use commit but stop for amending S squash use commit but meld into previous commit If you remove a line here THAT COMMIT WILL BE LOST However if you remove everything the rebase will be aborted He He it HE HE HE HE HE HE If instead of pick or edit you specify squash G
366. unk 79 4c93b258 373f 11de be05 5f7a86268029 Notice that the SHA checksum that originally started with 97031e5 when you committed now begins with 938b1a5 If you want to push to both a Git server and a Subversion server you have to push dcommit to the Subversion server first because that action changes your com mit data Pulling in New Changes If you re working with other developers then at some point one of you will push and then the other one will try to push a change that conflicts That change will be rejected until you merge in their work In git svn it looks like this git svn dcommit Committing to file tmp test svn trunk Merge conflict during commit Your file or directory README txt is probably out of date resource out of date try updating at Users schacon libexec git core git svn line 482 To resolve this situation you can run git svn rebase which pulls down any changes on the server that you don t have yet and rebases any work you have on top of what is on the server git svn rebase M README txt r80 ff829ab914e8775c7c025d741beb3d523ee30bc4 trunk First rewinding head to replay your work on top of it Applying first user change Now all your work is on top of what is on the Subversion server so you can successfully dcommit git svn dcommit Committing to file tmp test svn trunk M README txt Committed r81 M README txt r81 456cbe6337abe49154db70106d1836bc1332deed trunk
367. up to allow traffic through this port The Cons The downside of serving your repository over HTTP is that it s relatively inefficient for the client It generally takes a lot longer to clone or fetch from the repository and you often have alot more network overhead and transfer volume over HTTP than with any of the other network protocols Because it s not as intelligent about transferring only the data you need there is no dynamic work on the part of the server in these transactions the HTTP protocol is often referred to as a dumb protocol For more information about the differences in efficiency between the HTTP protocol and the other protocols see Chapter 9 Getting Git on a Server In order to initially set up any Git server you have to export an existing repository into a new bare repository a repository that doesn t contain a working directory This is generally straightforward to do In order to clone your repository to create a new bare repository you run the clone com mand with the bare option By convention bare repository directories end in git like so git clone bare my project my project git Initialized empty Git repository in opt projects my project git 84 CHAPTER 4 GIT ON THE SERVER The output for this command is a little confusing Because clone is basically agit init and thenagit fetch you see some output from the git init part which creates an empty directory The actual object transfer gives no
368. updates your local database moving your origin master pointer to its new more up to date position see Figure 3 24 To demonstrate having multiple remote servers and what remote branches for those remote projects look like let s assume you have another internal Git server that is used only for development by one of your sprint teams This server is at git team1 ourcompany com You can add it as a new remote reference to the project you re currently working on by running the git remote add command as I covered in Chapter 2 Name this remote teamone which will be your shortname for that whole URL see Figure 3 25 Now you can run git fetch teamone to fetch everything the server has that you don t have yet Because that server is a subset of the data your origin server has right now Git fetches no data but sets a branch called teamone master to point to the commit that teamone has as its master branch see Figure 3 26 65 66 CHAPTER 3 GIT BRANCHING git ourcompany com master My Computer Someone else pushes Figure 3 23 Working locally and having someone push to your remote server makes each history move forward differently git ourcompany com i git fetch origin My Computer origin master Figure 3 24 The git fetch command updates your remote references CHAPTER 3 GIT BRANCHING 67 git ourcompany com git team1 ourcompany com git remote add teamone git git teami ourcom
369. urce community to find and help you with CHAPTER 4 GIT ON THE SERVER 97 These days you have a huge number of hosting options to choose from each with differ ent advantages and disadvantages To see an up to date list check out the GitHosting page on the main Git wiki http git or cz gitwiki GitHosting Because I can t cover all the hosting sites and because I happen to work at one of them I ll use this section to walk through setting up an account and creating a new project at GitHub This will give you an idea of what is involved GitHub is by far the largest open source Git hosting site and it s also one ofthe very few that offers both public and private hosting options so you can keep your open source and pri vate commercial code in the same place In fact I used GitHub while writing this book GitHub GitHub is slightly different than most code hosting sites in the way that it namespaces proj ects Instead of being primarily based on the project GitHub is user centric That means when you host our grit project on GitHub you won t find it at github com grit but instead at github com schacon grit There is no canonical version of any project which allows a project to move from one user to another seamlessly if the first author abandons the project GitHub is also a commercial company that charges for accounts that maintain private repositories but anyone can quickly get a free account to host as many open source projects as t
370. x created 3a0874c fixed the broken email address 1 files changed 0 insertions 1 deletions master hotfix dt c3 iss53 Figure 3 13 hotfix branch based back at your master branch point You can run your tests make sure the hotfix is what you want and merge it back into your master branch to deploy to production You do this with the git merge command git checkout master git merge hotfix Updating f42c576 3a0874c Fast forward README 1 1 files changed 0 insertions 1 deletions You ll notice the phrase Fast forward in that merge Because the commit pointed to by the branch you merged in was directly upstream of the commit you re on Git moves the pointer forward To phrase that another way when you try to merge one commit with a commit that can be reached by following the first commit s history Git simplifies things by moving the pointer forward because there is no divergent work to merge together this is called a fast forward 56 CHAPTER 3 GIT BRANCHING Your change is now in the snapshot of the commit pointed to by the master branch and you can deploy your change see Figure 3 14 master Figure 3 14 Your master branch points to the same place as your hotfix branch after the merge After your super important fix is deployed you re ready to switch back to the work you were doing before you were interrupted However first you ll delete the hotfix bra
371. y edit the reference files Git provides a safer command to do this if you want to update a reference called update ref git update ref refs heads master 1a410efbd13591db07496601ebc7a059dd55cfe9 That s basically what a branch in Git is a simple pointer or reference to the head of aline of work To create a branch back at the second commit you can do this git update ref refs heads test cacoca Your branch will contain only work from that commit down git log pretty oneline test cac0cab538b970a37ea1e769cbbde608743bc96d second commit fdf4fc3344e67ab068f836878b6c4951e3b15f3d first commit Now your Git database conceptually looks something like Figure 9 4 CHAPTER 9 GIT INTERNALS bak 1a410e 3c4e9c refs heads master third commit tree new txt test txt 1f7a7a version 2 Era test txt refs heads test second commit fdf4fc first commit new txt Figure 9 4 Git directory objects with branch head references included 15Seb tree 83baae test txt version 1 When you run commands like git branch branchname Git basically runs that update ref command to add the SHA 1 of the last commit of the branch you re on into what ever new reference you want to create The HEAD The question now is when you run git branch branchname how does Git know the SHA 1 of the last commit The answer is the HEAD file The HEAD file is a symbolic reference to the branch you re currently on By
372. y specifying the new SHA 1 value that the hash object command gave you git tag a maintainer pgp pub 659ef797d181633c87ec71ac3f9ba29fe5775b92 CHAPTER 5 DISTRIBUTED GIT 141 Ifyou run git push tags the maintainer pgp pub tag will be shared with everyone If anyone wants to verify a tag they can directly import your PGP key by pulling the blob directly out of the database and importing it into GPG git show maintainer pgp pub gpg import They can use that key to verify all your signed tags Also if you include instructions in the tag message running git show lt tag gt will let you give the end user more specific instructions about tag verification Generating a Build Number Because Git doesn t have monotonically increasing numbers like v123 or the equivalent to go with each commit if you want to have a human readable name to go with a commit you can run git describe on that commit Git gives you the name of the nearest tag with the number of commits on top of that tag and a partial SHA 1 value of the commit you re describing git describe master V1 6 2 rc1 20 g8c5b85c This way you can export a snapshot or build and name it something understandable to people In fact if you build Git from source code cloned from the Git repository git version gives you something that looks like this If you re describing a commit that you have directly tagged it gives you the tag name Thegit describe command favors annotat
373. y stable code When you have work in a topic branch that you ve done or that someone has contributed and you ve verified you merge it into your master branch delete the topic branch and then continue the process If you have a repository that looks like Figure 5 19 with work in two branches named ruby client and php client and you merge ruby client first and then php client next your history will end up looking like Figure 5 20 OOO v ruby client php client ito me Figure 5 19 History with several topic branches 136 CHAPTER 5 DISTRIBUTED GIT 6 Gro 9 9 BE php_client Figure 5 20 After a topic branch merge That is probably the simplest workflow but it s problematic if you re dealing with larger repositories or projects If you have more developers or a larger project you ll probably want to use at least a two phase merge cycle In this scenario you have two long running branches master and develop in which you determine that master is updated only when a very stable release is cut and all new code is integrated into the develop branch You regularly push both of these branches to the public repository Each time you have a new topic branch to merge in Figure 5 21 you merge it into develop Figure 5 22 then when you tag a release you fast forward master to wherever the now stable develop branch is Figure 5 23 oe om a Figure 5 21 Before a topic branch me
374. you can specify older commits with this data as well If you want to see the fifth prior value of the HEAD of your repository you can use the n reference that you see in the reflog output git show HEAD 5 You can also use this syntax to see where a branch was some specific amount of time ago For instance to see where your master branch was yesterday you can type git show master yesterday That shows you where the branch tip was yesterday This technique only works for data that s still in your reflog so you can t use it to look for commits older than a few months 146 CHAPTER 6 GIT TOOLS To see reflog information inline with your normal log information you can run git log g git log g master commit 734713bc047d87bf7eac9674765ae793478c50d3 Reflog master 0 Scott Chacon lt schacon gmail com gt Reflog message commit fixed refs handling added gc auto updated Author Scott Chacon lt schacon gmail com gt Date Fri Jan 2 18 32 33 2009 0800 fixed refs handling added gc auto updated tests commit d921970aadf03b3cf0e71becdaab3147ba71cdef Reflog master 1 Scott Chacon lt schacon gmail com gt Reflog message merge phedders rdocs Merge made by recursive Author Scott Chacon lt schacon gmail com gt Date Thu Dec 11 15 08 43 2008 0800 Merge commit phedders rdocs It s important to note that the reflog information is strictly local it s a log of what you ve done in your repository
375. you can t do much when you aren t connected to the server and in Sub version and CVS you can edit files but you can t commit changes to your database because your database is offline This may not seem like a huge deal but you may be surprised what a big difference it can make Git Has Integrity Everything in Git is check summed before it is stored and is then referred to by that checksum This means it s impossible to change the contents of any file or directory without Git knowing about it This functionality is built into Git at the lowest levels and is integral to its philosophy You can t lose information in transit or get file corruption without Git being able to detect it The mechanism that Git uses for this check summing is called a SHA 1 hash This is a 40 character string composed of hexadecimal characters 0 9 and a f and calculated based on the contents of a file or directory structure in Git A SHA 1 hash looks something like this 24b9da6552252987aa493b5218696cd6d3b00373 You ll see these hash values all over the place in Git because it uses them so much In fact Git stores everything not by file name but in the Git database addressable by the hash value of its contents Git Generally Only Adds Data When you do actions in Git nearly all of them only add data to the Git database It is difficult to get the system to do anything that is undoable or to make it erase data As in any VCS you can lose or mess up changes y
376. you can think of should work Generating Your SSH Public Key That being said many Git servers authenticate using SSH public keys In order to provide a public key each user in your system must generate one if they don t already have one This process is similar across all operating systems First you should check to make sure you don t already have a key By default a user s SSH keys are stored in that user s ssh directory You can easily check to see if you have a key already by going to that directory and listing the contents cd ssh Is authorized keys2 id dsa known hosts config id dsa pub 86 CHAPTER 4 GIT ON THE SERVER You re looking for a pair of files named something and something pub where the something is usually id dsa or id_rsa The pub file is your public key and the other file is your private key If you don t have these files or you don t even have a ssh directory you can create them by running a program called ssh keygen which is provided with the SSH package on Linux Mac systems and comes with the MSysGit package on Windows ssh keygen Generating public private rsa key pair Enter file in which to save the key Users schacon ssh id_rsa Enter passphrase empty for no passphrase Enter same passphrase again Your identification has been saved in Users schacon ssh id_rsa Your public key has been saved in Users schacon ssh id rsa pub The key fingerprint is 43 C5 5b 5f b1
377. yright owner and the publisher The purchaser may print the work in full or in part for their own noncommercial use The purchaser may place the eBook title on any of their personal computers for their own personal reading and reference Offer valid through 2 10

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