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1. 0 1 1 s author Scott Chacon s email schacon gmail com s summary A simple gem for using Git in Ruby code SHOWING TREES Instead of the git show command it s generally more useful to use the lower level git ls tree command to view trees because it gives you the SHA 1s of all the blobs and trees that it points to git ls tree master tree 100644 blob 569b350811e7bfcb2cc781956641c3 README 100644 blob 8f94139338f9404f26296befa88755 Rakefile 040000 tree ae850bd698b2b5dfbaclab5fd95a48 lib You can also run this command recursively so you can see all the subtrees as well This is a great way to get the SHA 1 of any blob anywhere in the tree without having to walk it one node at a time git ls tree r t master tree 66 100644 blob 569b350811e7bfcb2cc781956641c README 100644 blob 8f94139338f9404f26296befa8875 Rakefile 040000 tree ae850bd698b2b5dfbaclab5fd95a4 lib 100644 blob 7e92ed361869246dc76f0cd0e526e lib simplegit rb The t makes it also show the SHA 1s of the subtrees themselves rather than just all the blobs SHOWING BLOBS Lastly you may want to extract the contents of individual blobs The cat file command is an easy way to do that and can also serve to let you know what type of object a SHA 1 is if you don t know It is sort of a catch all command that you can use to inspect objects git cat file t ae850bd698b2b5dfbac tree git cat file p ae850bd698b2b5dfbac 10064
2. or on yum based systems you can often run yum install git core Installing on Mac You are likely going to want to install Git without the asciidoc depen dency because it is a pain to install Other than that what you basically need is Curl and Expat With the exception of the Leopard binary OS X installer you will also need the Developer Tools installed If you don t have the OS x install discs anymore you can get the tools from the Apple Website http developer apple com tools Mac 10 4 Tiger There are some requirements you ll have to install before you can compile Git Expat can be installed roughly like this curl 0 http surfnet dl sourceforge net sourceforge expat expat 2 0 1 tar gz tar zxvf expat 2 0 1 tar gz cd expat 2 0 1 configure prefix usr local make make check sudo make install cd Then download and compile Git as per the Linux instructions However if you want an easier path you can use the excellent Mac Ports software To install MacPorts simply follow the instructions on the MacPorts Homepage http www macports org and then just run sudo port install git core For an in depth tutorial on installing on 10 4 see this article http blog kineticweb com articles 2007 08 26 compiling git for mac os x 10 4 10 intel If you hope to use Git with an existing Subversion repository pass the svn flag to port This will build Subversion and the necessary Perl interfaces for S
3. Author Scott Chacon Author Scott Chacon schacon gmail com You can also use git diff to show you some spiffy stats for a diff rather than a patch file if you want to see a wider overview of what changed then drill down into specific files later Here are some examples getting stats the first for the differences between two com mits and the second a summary between a commit and the current HEAD git diff numstat allbef06a3f65 cf25cc3bfbO 73 3 1 README 1 Rakefile 4 5 lib simplegit rb git diff stat 0576fac35 README 4 Rakefile 2 Llib simplegit rb 4 3 files changed If you want to see what the specific difference is in one of those files 8 insertions 2 deletions you can just add a path limiter to the diff command git diff allbefo diff git a Rakef 6a3f65 cf25cc3bfb0 Rakefile ile b Rakefile index a874b73 8f94139 100644 a Rakefile b Rakefile 5 7 5 7 require rake gempackagetask spec Gem Speci platform name version version author email summary NNN x code fication new do s Gem Platform RUBY simplegit HQ 0 QO 1 1 Scott Chacon schacon gmail com A simple gem for using Git in Ruby You can use this command to detect changes between your index and any tree or your working directory and any tree your working directory and your index etc Generating
4. Git Peepcode Screencast http peepcode com products git RailsCasts Git Screencast http railscasts com episodes 96 Using Git to Manage and Deploy Rails Apps http www jointheconversa tion org railsgit 120
5. In the end there is really no single right way to do it being a decentralized system you can have a model with all of these aspects to it or any combination you can think of You can also have sub groups using different models on the same codebase For example if your company might have an internal fork of the Linux kernel that is managed by the Integration Manager model in addition to pulling in changes occasionally from Linus s branch In the end you and your team will have to think about what will work best for you 104 Sharing Repositories Over Git Git provides its own special protocol which is basically just a really thin wrapper over the git upload pack command that will tell you what is available then you tell it what you have and it gives you a packfile of the difference To start it up manually run something like the following command git daemon detach export all base path opt git opt git ambition Though for long term running you ll likely want to add this to your inet d configuration See the git daemon http www kernel org pub soft ware scm git docs git daemon html docs for specific information on how to set that up The git protocol has no built in authentication so generally you cannot push over it although some people have open push policies and so allow that would not recommend setting that up so you ll have to look up how to do that If you want your users to have push access
6. a a60ae62dd2244a68d78151331067c5fb5d6b3e al Ibef06a3f659402 fe7563abf99ad00de2209e6 a8 74b732e12a5c04b5a73d7f1123c249997b0b2d a9 06cb2a4a904a152e80877d4088654daad0c859 el bBececbOcbaf2320ca3eebb8aa2beb1bb45c66 fe 897108953cc224f417551031beacc396b11fb0 info pack z refs heads l master tags z v0 1 o For more in depth information on the Git directory layout see the git repository layout docs http www kernel org pub software scm git docs repository layout html For now let s go over some of the more important contents of this directory git config This is the main Git configuration file It keeps your project specific Git options such as your remotes push configurations tracking branches and more Your configuration will be loaded first from this file then from a gitconfig file and then from an etc gitconfig file if they exist Here is an example of what a config file might look like core repositoryformatversion 0 filemode true bare false logallrefupdates true remote origin url git github com username myproject git fetch refs heads refs remotes origin branch master remote origin merge refs heads master See the git config http www kernel org pub software scm git docs git config html docs for
7. can con tinue the rebase This gives us some options since the rebase can do this at any point say you have 8 commits to move onto the new branch each one could cause a conflict and you will have to resolve them each manu ally The rebase command will stop at each patch if it needs to and let you do this You have three things you can do here you can either fix the file run a git add on it and then run a git rebase continue which will move on to the next patch until it s done Our second option is to run git rebase abort which will reset us to what our repo looked like before we tried the rebase Or we can run git rebase skip which will leave this one patch out abandoning the change forever Git rebase options for a conflict continue trys to keep going once you ve resolved it abort gives up altogether and returns to the state before the rebase skip skips this patch abandoning it forever 82 In this case we will simply fix the conflict run git add on the file and then run git rebase continue which then makes our history look like this limiting log to 30 added todo options added limit to log function fixed conflict new version 0 2 0 new version 0 1 2 added a new function rakefile and todo file added Then all we have to do is switch to the master branch and merge in story84 which is called a fast forward since master is now a
8. the information manager from hell Linus 4 7 05 When learned Git as many people do learned it in the context of other SCMs had used Subversion or Cvs have come to believe that this is a horrible way to learn Git felt far more comfortable with it when stopped thinking that git add was sort of like svn add but instead understood what it was actually doing Then found could find new and interesting ways to use what is really a very powerful and cool toolset Git l Subversion Magic So let s see what it s doing behind the scenes first What is Git Git is a stupid content tracker That is probably the best description of it don t think of it in a like insert favorite SCM system but context but more like a really interesting file system Git tracks content files and directories It is at its heart a collection of simple tools that implement a tree history storage and directory 10 content management system It is simply used as an SCM not really designed as one In many ways you can just see git as a filesystem it s content addressable and it has a notion of versioning but really really designed it coming at the problem from the viewpoint of a filesystem person hey kernels is what do and actually have absolutely zero interest in creating a traditional SCM system Linus http marc info l linux kernel amp m 111314792424707 When most SCMs store a new vers
9. Patch Files The default output of the git diff command is a valid patch file If you pipe the output into a file and email it to someone they can 74 apply it with the patch command If you ve done some work off of a project in an experiment branch you could create a patch file this way git diff master experiment gt experiment patch You can then email that file to anyone who could apply it with the p1 argument patch p1 lt experiment patch patching file lib simplegit rb e git diff http www kernel org pub software scm git docs git diff html Branching This is the fun part of Git that you ll come to love like a child When you first initialize a git repository or clone one you ll get a master branch by default if you don t specify something else This is really just a git suggestion and you don t have to use it like just about everything in Git it can be overridden Switching Branches However let s say we re working on our project and we want to add a new function to our library so we ll make a new branch called new func and switch to it There are two ways we can do this one is to create the branch and then switch to it git branch newfunc git checkout newfunc The other way is to checkout a branch that doesn t exist yet and tell BRANCHING AND MERGING SCREENCAST In this screencast we take you through a work flow where we branch stash and merge several ti
10. a darker color in this example 34 jen master t R1 co a _ t master At this point you both do work and commit changes and then you fetch and merge from her again Then she does another commit and you fetch and merge once more At this point you ll have a commit history that looks something like this jen master Rl lt R2 lt R3 master Perfectly fine but it can get a little confusing when you litter the history with all those commits that do nothing but merge unshared changes The longer you keep out of sync the worse this can get This is where the rebasing command comes in With rebase Git will checkout the upstream branch in this case Jen s master branch and 35 then replay all the changes you ve done since you forked on top of those files as if you had forked your work off at that point and done all your changes rather than earlier Rebase will literally produce a series of patch files of your work and start applying them to the upstream branch automatically making new commits with the same messages as before and orphaning your older ones These objects can then be removed since nothing points to them when you run the garbage collection tools see The Care and Feeding of Git section eee So let s see what happens if we rebase rather than merge t in the same scenario Here we have our first merge and we can see that it orphans Com ee ee mit 1 and applies t
11. all of this together into how all these objects relate to each other conceptually 21 The Git Data Model In computer science speak the Git object data is a directed acyclic graph That is starting at any commit you can traverse its parents in one direction and there is no chain that begins and ends with the same object All commit objects point to a tree and optionally to previous com mits All trees point to one or many blobs and or trees Given this simple model we can store and retrieve vast histories of complex trees of arbitrarily changing content quickly and efficiently This section is meant to demonstrate how that model looks References In addition to the Git objects which are immutable that is they cannot ever be changed there are references also stored in Git Unlike the objects references can constantly change They are simple pointers to a particular commit something like a tag but eas ily moveable Examples of references are branches and remotes A branch in Git is nothing more than a file in the git refs heads directory that con tains the SHA 1 of the most recent commit of that branch To branch that line of development all Git does is create a new file in that direc tory that points to the same SHA 1 As you continue to commit one of the branches will keep changing to point to the new commit SHA 1s while the other one can stay where it was If this is confusing don t worry We ll go over it ag
12. and remotes added for each one so could work on and contribute to either sr git wiki tork watch 4 download_ this repo is viewable by everyone ript A quick amp dirty git powered Sinatra wiki fomepage http atonie org 2008 02 git wiki Public Clone URL git github com sr git wiki git The git wiki network graph All branches in the network using sr git wiki as the reference point Read our blog post about how it works Show Help elliottcable ta E g adulau willcodeforfoc g bruce schacon talald al3x o e smartkiwi p FIG O Project network visualization 109 Let s say there is a popular feature request that is either not com pleted or not accepted by the main project maintainer You can very easily fork the project and keep your patch or patches up to date with the head on a regular basis and people can pull from yours instead Perhaps enough demand builds up or enough testing is done from all these users that the patch is accepted You can then delete your fork and revert to the original project head This will also really change patch submission for large projects Instead of emailing patches around you can fork the project add your patch and submit a pull request for your branch with the fix to one of the core members or through the ticketing system A mem ber of the core team can add you as a remote easily create a new testing branch merge in or rebase your branch test and acc
13. direct ancestor of story84 to get this limiting log to 30 added todo options added limit to log function fixed conflict new version 0 2 0 new version 0 1 2 added a new function rakefile and todo file added Interactive Rebasing Much like Git provides a nicer way to work with your index before committing with git add interactive there is an interactive rebasing option that can only be fairly described as the bee s knees Assume we have started working on a story to add the git add functionality to our library and so we ve started a new branch called story92 and done the work there Then we decide that the Is tree function needs to be recursive and make that change then we tweak the library again committing each time Meanwhile we ve pulled in 83 a change that implements the same Is tree change differently into our master branch added verbose option to add function made Is tree recursive added git add function made the Is tree function recursive and limiting log to 30 added todo options We can see before we try the merge that the same change is in each branch and can see that the master branch version is better so don t even really want to merge it just want to throw my change away Also don t really need the other two commits to be two com mits because the second one is just a tweak and should be included in the first one Lets use git rebase
14. ence is moved forward Let s also say at this point we tag this commit as a release which adds a new At this point we ll have the following in Git 24 HEAD tag branch Nat commit tree i blob tree Aa blob tree blob Notice how the other two blobs that were not changed were not added again The new trees that were added point to the same blobs in the data store that the previous trees pointed to Now let s say we modify the init rb file at the base of the project The new blob will have to be added which will add a new top tree but all the subtrees will not be modified so Git will reuse those refer ences Again the branch reference will move forward and the new commit will point to its parent 25 HEAD branch commit tree a 4 tree blob fos blob tree blob At this point let s stop to look at the objects we now have in our repository From this we can easily recreate any of the three directo ries we committed by following the graph from the most recent com mit object and having Git expand the trees that are pointed to For instance if we wanted the first tree we could look for the parent of the parent of the HEAD or the parent of the tag If we wanted the second tree we could ask for the commit pointed to by the tag and so on 26 tag i commit A commit tree tree tree blob tree tree blob tree blob blob HEAD branch lt
15. git docs git merge html e git reset http www kernel org pub software scm git docs git reset html e git revert http www kernel org pub software scm git docs git revert html Rebasing To review rebasing is an alternative to merging that takes all the changes you ve done since you branched off and applies those changes as patches to where the branch you are rebasing to is now abandoning your original commit objects For clean merges this is a relatively simple process Say we have been working in a branch called story84 and it s completed and we want to merge it into the master branch 80 added limit to log function limiting log to 30 added todo options fixed conflict new version 0 2 0 new version 0 1 2 added a new function rakefile and todo file added Revert rakefile and todo file added rakefile and todo file added If we do a simple merge our history will look like this fixed conflict limiting log to 30 added todo options added limit to log function fixed conflict But we don t want to mess up our history with a bunch of branches and merges when it can be clearer Instead of running git merge story84 from the master branch we can stay in the story84 branch and run git rebase master git rebase master First rewinding head to replay your work on top of it HEAD is now at 2cQd4d7 added limit to log function Applying added todo options Adds trailing whitespace
16. i to rebase this branch and make those changes When we run the command our editor comes up showing this Rebasing c110d7f c4f10f2 onto c110d7f Commands pick use commit edit use commit but stop for amending squash use commit but meld into previous commit If you remove a line here THAT COMMIT WILL BE LOST pick 2b6ae91 added git add function pick bdfd292 made ls tree recursive pick c4f10f2 added verbose option to add Now we can see all of the commits that we are going to rebase If we remove the made Is tree recursive line it effectively ditches that commit so we ll avoid a conflict and not have to worry about it Changing the action on the last line to squash tells git to just make this and the previous commit into a single commit So if we exit the editor with this as the new text 84 pick 2b6ae91 added git add function squash c4f10f2 added verbose option to add function Then git sees we have squashed two commits and wants us to pick a commit message for it giving us the commit messages of both for us to create a new one for This is a combination of two commits The first commit s message is added git add function This is the 2nd commit message added verbose option to add function Please enter the commit message for your changes Comment lines starting with will not be included Not currently on any branch Changes to be committ
17. identifier of fixed length that uniquely identifies a specific piece of content SHA 1 succeeded SHA O and is the most commonly used algorithm Wikipedia http en wikipedia org wiki SHA1 has more on the topic To demonstrate these examples we will develop a small ruby library that provides very simple bindings to Git keeping the project in a Git repository The basic layout of the project is this Working Directory FIG A Sample project with files and directories Let s take a look at what Git does when this is committed to a reposi tory 14 The Blob In Git the contents of files are stored as blobs Working Directory Git Directory ERNEA ie blob a874b7 EEE gt blob a906cb dT gt blob a0a60a FIG B Files are stored as blobs It is important to note that it is the contents that are stored not the files The names and modes of the files are not stored with the blob just the contents This means that if you have two files anywhere in your project that are exactly the same even if they have different names Git will only store the blob once This also means that during repository transfers such as clones or fetches Git will only transfer the blob once then expand it out into multiple files upon checkout 15 FIG C The contents of a blob uncompressed 16 The Tree Directories in Git basically correspond to trees Working Directory ae gt ne gt gt Gx FIG
18. is in your index the staged column is what will be committed when you run git commit You can also do more complicated things like going through all of your change patches hunk by hunk deciding if each hunk should be applied to the next commit or not This means that if you ve made a bunch of changes to one file you can commit part of those changes in one commit and the rest in a second Try the patch menu option in the Interactive Adding menu to try this out Beware of using interactive adding if you are already used to running git commit a If you run through the whole interactive add process and then run git commit a it will basically ignore everything you just did and just add all modified files REMOVING For removing files from your tree you can simply run git rm lt filename gt 62 This will remove that file from the index and thus from the next com mit as well as from your working directory On your next commit the tree that commit points to will simply not contain that file anymore Log the Commit History So now we have all this history in our Git repository So what What can we do with it How can we see this history The answer is the very powerful git log command The log com mand can show you nearly anything you want to know about your commit history Also since the entire history is stored locally it s really fast compared with most other SCM systems especially if your repository is packed see
19. is that you need to run git update server info each time you commit to the repository git update server info It is generally a good idea to put this in the post commit hook file on any server that you want to be able to fetch from over HTTP Actually you can run this without update server info if you never pack objects and you have a pre defined list of branches you are always fetching All update server info does is put a list of 106 branches into one file git info refs and a list of pack files into another git objects info pack to get around the fact that you cannot reliably list contents of a directory over HTTP it s not built into the protocol So for Git to know what packfiles and branches are available it needs to have one URL it can get those from Hosted Repositories If you don t want to deal with setting up and maintaining your own server for your git repository you can use one of the growing number of public Git hosted servers will focus on some interesting features of a commercial service called GitHub http github com here but there is also an open source project called Gitorious http gitorious com that has many of the same features One of the compelling features of GitHub is the ability to create a private repository and share it with only a few developers However the complete source to Gitorious is available as a Ruby on Rails application It could be modified to run on your company s serv
20. it So if it s not built specifically to be an SCM 49 perhaps it would be useful to see some other examples of things it might be good for This is a simple listing of some other tools that have been built on Git internals to demonstrate that an SCM is the bundled application but Git can also be a useful toolkit for any application needing to track and manage slowly changing distributed trees of content Peer to Peer Content Distribution Network Imagine you are a retail chain or university campus and have a network of digital signage displays that play flash content advertise ments or show campus news etc You have to get new content out to them every day or two which may consist of any combination of XML files images animations text and sound You need to build a content distribution framework that will easily and efficiently transfer all the necessary content to the machines on your network You need to constantly determine what content each machine has and what it needs to have and transfer the difference as efficiently as possible because networking to these units may be spotty It turns out that Git is an excellent solution to this problem You can simply check all the needed content into Git create a branch for each unit and point that branch to the exact subtree of content it needs Then at some interval you have the unit fetch its branch If nothing has changed nothing happens if content has changed somehow
21. merge the changes and delete our experiment branch Our history of commit objects now looks like this T1 master C4 lt C6 i a C2 lt C3 lt C5 co lt Cl 31 Remotes Now lets take a look at remotes Remotes are basically pointers to branches in other peoples copies of the same repository often on other computers If you got your repository by cloning it rather than initializing it you should have a remote branch of where you copied it from automatically added as origin by default Which means the tree that was checked out during your initial clone would be refer enced as origin master which means the master branch of the origin remote Lets say you clone someone s repository and make a few changes You would have two references one to origin master which points to where the master branch was on the person s repository you cloned from when you did so and a master branch that points the most recent local commit origin master master t t cO lt Cl lt C2 Now let s say you run a fetch A fetch pulls all the refs and objects that you don t already have from the remote repository you specify By default it is origin but you can name your remotes anything and you can have more than one Suppose we fetch from the repository that we originally cloned from and they had been doing some work They have now committed a few times on their master branch but they al
22. of a Tag object pointing to that commit Unlike object Tags these can be moved around easily which is generally undesirable 90 Signed Tags At the other end of the tagging spectrum you can sign Tag object with a GPG key to ensure its cryptographic integrity Replacing a with s in the command will create a Tag object and sign it with the current users email address GPG key If you want to specify a key you can run it with u instead git tag u lt key id gt v0 1 m the 0 1 release Then you or others can later verify that signed tag with a v git tag v v0 1 e git tag http www kernel org pub software scm git docs git tag html Exporting Git If you want to create a release of your code or provide some poor non git user with a snapshot of just a specific tree you can use the git archive command git archive used to be called git tar tree in case you ever see that command around in older articles You can create the archive in either tar or zip formats the default being tar You can use the prefix argument to determine what directory if any the files are expanded into To create a gzipped tar ball you ll have to pipe the output through gzip first git archive prefix simplegit v0 1 gzip gt simple git 0 1 tgz 91 Then if you email that tarball to someone they would get this when they opened it tar zxpvf simple git 0 1 tgz simpleg
23. space though so there are ways to limit and format this output differently pretty is a useful option for formatting the output in different ways For example we can list the commit SHA 1s and the first line of the message with pretty oneLine git log pretty oneline cf25cc3bfbOece7dc3609b8dcOc committing all changes Oc8a9ec46029a4e92a428cb98c9 changed the verison number 0576fac355dd17e39fd2671b010 my second commit which is allbef06a3f659402fe7563abf9 first commit With pretty you can choose between oneline short medium full fuller email raw and format string where string is a format you specify with variables ex format an added h on ar will give you a bunch of lines like Scott Chacon added flcc9df 4 days ago 64 Filtering Log Output There are also a number of options for filtering the log output You can specify the maximum number of commits you want to see with n you can limit the range of dates you want to see commits for with since and until you can filter it on the author or committer text in the commit message and more Here is an example showing at most 30 commits between yesterday and a month ago by me git log n 30 since 1 month ago until yesterday author schacon e git log http www kernel org pub software scm git docs git log html Browsing Git Git also gives you access to a number of lower level tools that can be used to browse the repository inspect
24. that branch in your repository yester day This value is relative to your repo your master yesterday will likely be different than someone else s even on the same project whereas the SHA 1 values will a ways point to the same commit in every copy of the repository ORDINAL SPEC master 5 This indicates the 5th prior value of the master branch Like the Date Spec this depends on special files in the git log directory that are written during commits and is specific to your repository CARROT PARENT e65s46 2 master 2 This refers to the Nth parent of that commit This is only really help ful for commits that merged two or more commits it is how you 42 can refer to a commit other than the first parent TILDE SPEC e65s46 5 The tilde character followed by a number refers to the Nth genera tion grandparent of that commit To clarify from the carrot this is the equivalent commit in caret syntax e65s46 master 2 master 2 R1 lt R2 lt _ R3 t 4 t master master 4 master master TREE POINTER e65s46 tree This points to the tree of that commit Any time you add a tree to any commit ish it resolves to its tree BLOB SPEC master path to file 43 This is very helpful for referring to a blob under a particular commit or tree The Git Directory When you initialize a Git repository either by cloning an existing one or creating a new one the first t
25. the Care and Feeding section If you just run git log you will get output like this git log commit cf25cc3bfb0ece7dc3609b8dc0cc4alel19f fbcd4 Author Scott Chacon lt schacon gmail com gt Date Mon Mar 17 21 52 20 2008 0700 committing all changes commit O0c8a9ec46029a4e92a428cb98c9693F09 F69a3 Ff fF Author Scott Chacon lt schacon gmail com gt Date Mon Mar 17 21 52 11 2008 0700 changed the verison number commit 0576fac355dd17e39fd2671b010e36299F713b4d Author Scott Chacon lt schacon gmail com gt Date Sat Mar 15 16 40 33 2008 0700 my second commit which is better than the first GIT LOG OPTIONS SCREENCAST The next screencast is on git log which demonstrates most of the major features and options to the git log command It includes showing the stat short stat and name stat options the pretty options the since and until limiters the path limiter and author field searching 63 commit allbef06a3f659402fe7563abf99ad00de2209e6 Author Scott Chacon lt schacon gmail com gt Date Sat Mar 15 10 31 28 2008 0700 first commit This will show you the SHA 1 of each commit the committer and date of the commit and the full message starting from the last com mit on your current branch and going backward in reverse chrono logical order so if there are multiple parents it just squishes them together interleaving the commits ordered by date Formatting Log Output The default format takes up a lot of
26. the status and contents of any of the objects and are generally helpful for inspection and debug ging Showing Objects The git show command is really useful for presenting any of the objects in a very human readable format Running this command on a file will simply output the contents of the file Running it on a tree will just give you the filenames of the contents of that tree but none of its subtrees Where it s most useful is using it to look at commits SHOWING COMMITS If you call it on a tree ish that is a commit object you will get simple information about the commit the author message date etc and a diff of what changed between that commit and its parents GIT OBJECT BROWSING SCREENCAST In this screencast we show how to browse and inspect raw Git objects The major tools covered are the git cat file and git ls tree com mands to inspect the object contents and then we cover some of the included graphical brows ers gitk and gitweb 65 git show master commit O0c8a9ec46029a4e92a428cb98c9693F09 F69a3 Ff fF Author Scott Chacon lt schacon gmail com gt Date Mon Mar 17 21 52 11 2008 0700 changed the verison number diff git a Rakefile b Rakefile index a874b73 8f94139 100644 a Rakefile b Rakefile 5 7 5 7 require rake gempackagetask spec Gem Specification new do s s platform Gem Platform RUBY s name simplegit s version 0 1 0 s version
27. 3 19 Do git add as a builtin Linus Torvalds lt torvalds osdl org 2006 05 17 09 33 32 Clean up git ls file directory walking library inte Linus Torvalds lt torvalds osdl org 2006 05 16 19 46 16 libify git Is files directory traversal Linus Torvalds lt torvalds osdl org 2006 05 16 19 02 14 Merge branch jc gitlink into next Junio C Hamano lt junkio cox net gt 2006 05 17 03 16 50 read tree reorganize bind_merge code Junio C Hamano lt junkio cox net gt 2006 05 17 03 16 27 Merge branch ew pretty fmt into next Junio C Hamano lt junkio cox net gt 2006 05 17 03 04 14 commit allow pretty args to be abbreviated Eric Wong lt normalperson yhbt ne 2006 05 14 17 20 46 Merge branch jc grep into next Junio C Hamano lt junkio cox net gt 2006 05 17 02 59 46 builtin grep workaround for non GNU grep Junio C Hamano lt junkio cox net gt 2006 05 17 02 48 13 Merge branch master into next Junio C Hamano lt junkio cox net gt 2006 05 16 17 21 35 Remove old git grep sh remnants Linus Torvalds lt torvalds osdl org 2006 05 16 16 46 31 Merge branch maint Junio C Hamano lt junkio cox net gt 2006 05 16 17 21 02 merge base Clarify the comments on post processing Junio C Hamano lt junkio cox net gt 2006 05 16 17 18 22 lindata tha dacnumantatian far alt maraa hana ECradeil Vek dman sferala NAC Aada INC OC 10 99 C0 910 SHAT exes 16s LetaveRe ne Tare 2320226048877 E gt I a Com prev commit containing
28. 4 branch will be the same After we fetch they will be different origin story84 will now point to one of the new commit objects we downloaded during the fetch At this point we may want to merge origin story84 into our local story84 branch That s easy enough but if we want to do it auto matically every time we fetch we can use git pull which is just a fetch and then a merge command So these commands are functionally equivalent git pull origin story84 git fetch origin story84 git merge origin story84 e git fetch http www kernel org pub software scm git docs git fetch html e git pull http www kernel org pub software scm git docs git pull html Pushing Now we can get updates from other repositories but how can we push changes to them If we have commit rights on the repository normally over SSH we can simply run git push 97 git push origin master The origin in that case will be inferred if you leave it out but if you ve used a different name for your remote or you are trying to push one of your other branches you can do that too git push scott public experimental If you don t specify a branch it will infer that you want to push every branch that you and the server have in common So if you have pushed your master branch and your experimental branch to the scott public server at any point running this will update the server to have the newe
29. 4 blob 7e92ed361869246dc76 simplegit rb git cat file t 569b350811 blob git cat file p 5696350811 SimpleGit Ruby Library This library calls git commands and returns the output It is an example for the Git Peepcode book Author Scott Chacon With those basic commands you should be able to explore and inspect any object in any git repository relatively easily 67 Graphical Interfaces There are two major graphical interfaces that come with Git as tools to browse the repository GITK A very popular choice for browsing Git repositories is the Tcl Tk based browser called gitk If you want to see a simple visualization of your repository gitk is a great tool Merge branch It grep into next Junio C Hamano lt junkio cox net gt 2006 05 17 15 52 16 builtin grep workaround for non GNU grep Linus Torvalds lt torvalds osdl org 2006 05 17 11 12 22 Merge branch ew pretty fmt Junio C Hamano lt junkio cox net gt 2006 05 17 15 49 23 Merge branch jc apply Junio C Hamano lt junkio cox net gt 2006 05 17 15 47 33 Merge branch jc grep into next Junio C Hamano lt junkio cox net gt 2006 05 17 15 52 03 Revert builtin grep workaround for non GNU grep Junio C Hamano lt junkio cox net gt 2006 05 17 11 42 14 Merge branch It dirwalk into next Junio C Hamano lt junkio cox net gt 2006 05 17 15 32 45 builtin add warn on unmatched pathspecs Linus Torvalds lt torvalds osdl org 2006 05 17 13 2
30. D Trees are pointers to blobs and other trees Git Directory tree 1a738d blob a874b7 blob a906cb tree fe8971 blob a0a60a A tree is a simple list of trees and blobs that the tree contains along with the names and modes of those trees and blobs The contents section of a tree object consists of a very simple text file that lists the mode type name and sha of each entry SSeSaa gt tree 1a738d Zlib Deflate 100644 blob a906cb README 100644 blob a874b7 Rakefile 040000 tree fe8971 lib FIG E An uncompressed tree 17 The Commit So now that we can store arbitrary trees of content in Git where does the history part of tree history storage system come in The answer is the commit object Working Directory Git Directory gt tree 1a738d EEEE gt blob a874b7 ees ee ere gt blob a906cb gt tree fe8971 gE gt blob a0a60a commit allbef FIG F A commit references a tree The commit is very simple much like the tree It simply points to a tree and keeps an author committer message and any parent com mits that directly preceded it 18 commit content size 0 tree 1a738d author Scott Chacon lt schacon gmail com gt 1205602288 committer Scott Chacon lt schacon gmail com gt 1205602288 y first commit FIG G Uncompressed initial commit Since this was my first commit there are no parents If commit a second time the
31. ain later 22 The Model The basic data model I ve been explaining looks something like this HEAD i remote branch tag a commit blob The cheap references I ve represented as the grey boxes the immu table objects are the colored round cornered boxes An Example Lets look at an example of simple usage of Git and which objects are stored in the Git object database as we go To begin with we commit an initial tree of three files and two sub directories each directory with one file in it Possibly something like this init rb Lib base l base_include rb 23 my_plugin rb When we first commit this tree our Git model may look something like this HEAD Y branch t commit tree a tree blob Tx tree blob blob tag object We have three trees three blobs and a single commit that points to the top of the tree The current branch points to our last commit and the HEAD file points to the branch we re currently on This lets Git know which commit will be the parent for the next commit Now let s assume that we change the lib base base_include rb file and com mit again At this point a new blob is added which changes the tree that points to it which changes the tree that points to that tree and so on to the top of the entire directory Then a new commit object is added which points to its parent and the new tree then the branch refer
32. and packfiles over a number of calls instead of packing them up but it is simple git clone http git gitorious org piston mainline git piston Once you have run one of these commands you will have a copy of the git repository full of all the history basically every blob and tree and commit that project has ever had This is really a full backup of the repository if the main server ever goes down or gets corrupted everyone who has ever cloned it has a fully capable backup that can replace it With Git there is really no single point of failure e git clone http www kernel org pub software scm git docs git clone html Fetching and Pulling So let s say that we re going to hack on TicGit our git based ticket tracking system project After we clone it we look through the source code but don t do anything right away After some time passes we come back to the project but it may not still be up to date changes may have occurred in the meantime So we fetch an update git fetch origin 96 This will contact the server over the same protocol we used to clone it and grab all of the objects and references that have been added since our clone and update our origin branch branches to point to what the server is pointing at now So if we did create a tracking branch on story84 and it was changed on the server someone pushed an update before we fetch our local story84 branch and our remote origin story8
33. apter covers some examples of what you will use in order to collaborate with other developers on a code base Cloning If you want to begin working on an existing project you will need to get an initial version of it copy its repository of objects and refer ences to your machine This is done with a clone Git can clone a 94 repository over several transports including local HTTP HTTPS SSH its own git protocol and rsync The git protocol and SSH are pre ferred because they are more efficient and not difficult to set up When you clone a repository it in essence copies all the git objects to a new directory checks you out a single local branch named the same as the HEAD branch on the cloned repo normally mas ter and stores all the other branches under a remote reference by default named origin That means that if we cloned the repo in the previous examples instead of story84 being a local branch you can switch to it becomes origin story84 that you have to create a local branch to pull into in order to work on eg git checkout track story84 origin story84 The track indicates that you may want to pull from or push to the origin of this branch later so remember where it came from LOCAL CLONES Local clones are the simplest types of clones it is basically the equivalent of copying the git directory and doing a checkout The only major difference is that it adds all the original bran
34. as e git stash http www kernel org pub software scm git docs git stash html Tagging As we previously covered creating a tag in Git is much like making a branch A tag in Git serves is basically a signed branch that never moves it is simply an arbitrary string that points to a specific com mit For example if you wanted to tag your code base every time you released to production or created a new binary to release you would run something like this git tag a v0 1 m this is my v0 1 tag As we recall from section one that command will create a git object that looks something like this 89 SSeS gt tag 0c819c tag content size 0 object 0576fa type commit tag v0 1 tagger Scott Chacon lt schacon gmail com gt 1205624655 this is my v0 1 tag and will store that in the git objects directory and then will create a permanent reference to it in git refs tags vo 1 that contains the SHA 1 of that tag Then you can use that as a reference to that commit at any time in commands like diff or archive see next chapter Lightweight Tags You can also create a tag that doesn t actually add a Tag object to the database but just creates a reference to it in the git refs tags directory If you run the following commana git tag v0 1 Git will create the same file as before git refs tags vo 1 but it will contain the SHA 1 of the current HEAD commit itself not the SHA 1
35. associate a name and email address One of the first things you ll want to do in Git is to set these values You can set them as global configuration values with the git config command git config global user name Scott Chacon git config global user email schacon gmail com This will create a new gitconfig file that will look like this cat gitconfig user name Scott Chacon email schacon gmail com You can change those variables at any time either by editing that SETUP INIT AND CLONING SCREENCAST have produced a series of short screencasts demonstrating the topics of several of the chapters in this book so you can see them in practice on a real command line You should be able to download these movies with this book from the PeepCode website The first in this series is Git Setup Initializa tion and Cloning and shows you how to setup your Git configuration how to initialize a new repository and how to clone an existing reposi tory over both the Git transport and the HTTP transport 54 file or running the git config commands again If you want to set different values for a specific project just leave out the global and it will write the same snippet into your git config file in that repository which will overwrite your global values e git config http www kernel org pub software scm git docs git config htm Getting a Git Repository There are two major ways you will get a Gi
36. atch file for one to apply to the other but what we really want to do next is merge the two e git branch http www kernel org pub software scm git docs git branch html e git checkout http www kernel org pub software scm git docs git checkout html Simple Merging So now we want to move the changes in our newfunc branch back into our master branch and remove it This will require us merging one branch into another Since we re already in our master branch we ll merge in the newfunc branch like this git merge newfunc Easy peasy We can see that the simplegit rb file now has four new lines and the README file was auto merged Now we can get rid of our newfunc branch with a simple git branch d newfunc Deleted branch newfunc Resolving Conflicts That was a fairly simple problem but what if we branch our code and then edit the same place in a file in different ways in each branch 77 In that case we ll get a conflict when we try to merge them back together Git is not too aggressive in trying to resolve conflicts since you don t want it to make assumptions that are not necessarily cor rect so bugs aren t introduced without your knowledge Let s say that we created a versioning branch and then modified the version in the Rakefile to different versions in both the new branch and the master branch then tried to merge them together git merge versioning Auto merged Rakefile CONFLICT content Merge con
37. but is pretty cool when you want to do anything non standard with it Git is less a program and more a toolkit that can be combined and chained to do new and interesting things For a long time Git was just the raw toolkit and the project to wrap those into a user friendly SCM was called Cogito That project has since been abandoned as Git itself became easier to use The tools can be more or less divided into two major camps often referred to as the porcelain and the plumbing The plumbing is not really meant to be used by people on the command line but rather to do simple things flexibly and are combined by programs and scripts into porcelain programs The porcelain programs are largely what we will be focusing on in this book the user oriented interfaces to do SCM type things hiding the low level fun Git Object Types Git objects are the actual data of Git the main thing that the reposi tory is made up of There are four main object types in Git the first three being the most important to really understand the main func tions of Git All of these types of objects are stored in the Git Object Database which is kept in the Git Directory Each object is compressed with 13 Zlib and referenced by the SHA 1 value of its contents plus a small header In the examples will use the first 6 characters of the SHA 1 for simplicity but the actual value is 40 characters long SHA stands for Secure Hash Algorithm A SHA creates an
38. ches in as origin branches Often you will do this when creating a bare reposi tory that is a repository without a working directory for putting on a public server or if you re working with people using a shared reposi tory over NFS or something similar git clone bare simplegit git simplegit bare git SSH AND GIT TRANSPORTS Cloning over SSH requires that you have user credentials on the machine you are cloning from The git transport does not have this authentication and so is normally used for fetching only DISTRIBUTED WORKFLOW SCREENCAST This screencast demonstrates a distributed workflow It takes two personas creating a project in GitHub and pushing to it in the first persona then cloning that project in the sec ond The second sets up a public read only HTTP repository on his own server The first then fetches from that merges changes and pushes back to GitHub It also demonstrates an instance in which the Author and Committer fields can differ for a commit 95 git clone git github com schacon ticgit git ticgit_ directory HTTP AND HTTPS TRANSPORTS Another popular way to clone a repository is over HTTP just because it is so simple You don t need to setup any special service or give out user credentials made easier by services like gitosis you simply scp your bare repository into any web server s static content directory It is not as efficient as the other protocols it will transfer loose objects
39. commit tree a blob So to keep all the information and history on the three versions of this tree Git stores 16 immutable signed compressed objects Traversal So what do all the arrows in these illustrations really mean How does Git actually retrieve these objects in practice Well it gets the initial SHA 1 of the starting commit object by looking in the git refs directory for the branch tag or remote you specify Then it tra verses the objects by walking the trees one by one checking out the 27 blobs under the names listed 1 git checkout v0 1 t 2 git refs tags v0 1 gt 0c819c 3 tag 0c819c a commit allbef Y tree 1a738d Rakefile blob a874b7 README blob a906cb tree fe8971 simplegit rb blob a0a60a Branching and Merging Here we come to one of the real strengths of Git cheap inline branching This is a feature that truly sets it apart and will likely change the way you think about developing code once you get used to it 28 When you are working on code in Git storing trees in any state and keeping pointers to them is very simple as we ve seen In fact in Git the act of creating a new branch is simply writing a file in the git refs heads directory that has the SHA 1 of the last commit for that branch Creating a branch is nothing more than just writing 40 characters to a file Switching to that branch simply means having Git make
40. commit object will look more like this commit content size 0 tree elb3ec parent allbef author Scott Chacon lt schacon gmail com gt 1205624433 committer Scott Chacon lt schacon gmail com gt 1205624433 my second commit which is better than the first FIG H A commit with a parent Notice how the parent in that commit is the same SHA 1 value of the last commit we did Most times a commit will only have a single parent like that but if you merge two branches the next commit will point to both of them commit commit allbef a d991 19 The current record for number of commit parents in the Linux kernel is 12 branches merged in a single commit 20 The Tag The final type of object you will find in a Git database is the tag This is an object that provides a permanent shorthand name for a par ticular commit It contains an object type tag tagger and a mes sage Normally the type is commit and the object is the SHA 1 of the commit you re tagging The tag can also be GPG signed providing cryptographic integrity to a release or version Sonon gt tag 0c819c tag content size 0 object 0576fa type commit tag v0 1 tagger Scott Chacon lt schacon gmail com gt 1205624655 this is my v0 1 tag FIG Uncompressed tag We ll talk a little bit more about tags and how they differ from branches which also point to commits but are not stored as objects in the next section where we ll pull
41. d there which can be over HTTP HTTPS SSH or the special git protocol We will use the public hosted repository of the simple library mentioned at the beginning of the book git clone git github com schacon simplegit git This will by default create a new directory called simplegit and do an initial checkout of the master branch If you want to put it in a different directory than the name of the project you can specify that on the command line too git clone git github com schacon simplegit git my_directory e git clone http www kernel org pub software scm git docs git clone html 56 Normal Workflow Examples Now that we have our repository let s go through some normal work flow examples of a single person developing Ignoring First off we will often want Git to automatically ignore certain files often ones that are automatically generated during our development For example in Rails development we often want to ignore the log files the production specific configuration files etc To do this we can add patterns into the gitignore file to tell Git that we don t want it to track them Here is an example gitignore file tmp log config database yml config environments production rb e gitignore http www kernel org pub software scm git docs gitignore html Adding and Committing Now we ll do some development and periodically commit our changes We have a few options here we can commit indi
42. d to dm core about 6 hours ago 987e2ad5699759cefb45ad 1c0a82cd80156bc671 Code reformatting and refactoring of initialization methods Blake Mizerany committed to sinatra about 14 hours ago MPS 99572b400d406c71 1e7a1d9100887c4b21b07Ide Watched Repositories jamis capistrano tobi delayed_job sam dm core sr dst defunkt facebox al3x git wiki sr git wiki FIG N Custom GitHub home page with your projects More interestingly you can publicly fork a project to get your own copy of it GitHub is unique in concept in thot it is really centered around individuals rather than projects For instance if you want to follow or work on Merb you would follow or fork wycats s Merb There is really no official Merb page in GitHub It s simply that wycats is known to be the blessed repository by the Merb project In fact Rails itself has recently been forked http github com ezmobius 108 rails tree master and significantly enhanced by Ezra Zygmuntowicz In other contexts this would be a bold divisive gesture but with Git it s common practice You could just as easily follow and fork someone else s repository of the project An interesting example of this is the git wiki http github com sr git wiki project which was started by a user named sr then was forked and greatly modified by al3x sr wanted to keep the project simple so now there are two major versions of the project have a checkout of the project
43. dotest patch 12 add warning 1 line adds whitespace errors Wrote tree 2d0bd54dc9e4c398769cdcb59256ca03bb482ccb Committed b669c78acffaafd5ba34449e7 faf88217394864a Applying limiting log to 30 error patch failed lib simplegit rb 14 error lib simplegit rb patch does not apply Using index info to reconstruct a base tree REBASING SCREENCAST This screencast follows roughly the same course as the previous one on branching and merging only we replace merging with rebas ing This screencast also demonstrates the interactive rebase command git rebase i We also demonstrate some slightly more com plex branching by using both interactive and normal rebasing techniques simultaneously on separate branches then choosing one and deleting the other 81 Falling back to patching base and 3 way merge Auto merged lib simplegit rb CONFLICT content Merge conflict in lib simplegit rb Failed to merge in the changes Patch failed at 0002 When you have resolved this problem run git rebase continue If you would prefer to skip this patch instead run git rebase skip To restore the original branch and stop rebasing run git rebase abort Many times this goes very smoothly and you can see all the new commits and trees written in place of the old ones In this case had edited the lib simplegit rb file differently in each branch which caused a conflict will have to resolve this conflict before
44. e contents of it will generally look like this ref refs heads master 47 git hooks This directory contains shell scripts that are invoked after the Git commands they are named after For example after you run a com mit Git will try to execute the post commit script if it has executable permissions See the online hooks documentation http www kernel org pub software scm git docs hooks html for more information on what you can do with hooks Working Directory The working directory is the checkout of the current branch you are working on What is really important to note here is that this code is a working copy it is not really important This is something that developers from most other SCMs have a hard time understanding and tends to scare them mightily If you check out a different branch Git will make your working directory look like that branch removing any checked in content that is cur rently in your working directory that is not in the new tree This is why Git will only let you checkout another branch if everything is checked in there are no uncommitted modified files The reason for this is that Git will remove files that are not necessary in the branch you are checking out it needs to make sure that you can get them back again Most users don t like to see content automatically removed from their directories but that s one of the mental shifts you ll need to make Your working directory is tempora
45. ed use git reset HEAD lt file gt to unstage modified Llib simplegit rb So we stick with the first message save and exit the editor git rebase i master Created commit 8341085 added git add function 1 files changed 4 insertions 0 deletions Successfully rebased and updated refs heads story92 Now we ve rebased and instead of three commits on top of our master and having to reconcile a useless conflict we ve just added a single commit with no resolving neccesary 85 added git add function made the Is tree function recursive limiting log to 30 added todo options The rebase command is one of the most useful and unique in the git workflow To learn more about some spiffy things you can do with it check out the History Manipulation and Advanced Merging sec tions e git rebase http www kernel org pub software scm git docs git rebase html e git reset http www kernel org pub software scm git docs git reset html Stashing Stashing is a pretty simple concept that is incredibly useful and very easy to use If you are working on your code and you need to switch to another branch for some reason and don t want to commit your current state because it is only partially completed you can run git stash which will basically take the changes from your last commit to the current state of your working directory and store it temporarily In the following example have a change t
46. emote you can fetch from again and possibly push to 111 if you have permission git add http www kernel org pub software scm git docs git add html Adds changes in files in your working directory to your index or staging area git rm http www kernel org pub software scm git docs git rm html Removes files from your index and your working directory so they will stopped being tracked git commit http www kernel org pub software scm git docs git commit html Takes all of the changes staged in the index that have been git add ed creates a new commit object pointing to it and advances the branch to point to that new commit git status http www kernel org pub software scm git docs git status html Shows you the status of files in your index versus your working directory It will list out files that are untracked only in your working directory modified tracked but not yet updated in your index and staged added to your index and ready for committing 12 git branch http www kernel org pub software scm git docs git branch html Lists existing branches including remote branches if a is provided Creates a new branch if a branch name is provided Branches can also be created with b option to git checkout git checkout http www kernel org pub software scm git docs git checkout html Checks out a different branch makes your working directory look like the tree of the commi
47. ept or reject If your patch is ignored or the team doesn t have time to deal with it yet it s easy to keep up to date by continually rebasing and re sending the pull requests until it s either rejected or accepted It doesn t just go stale until it s difficult to apply the patch anymore Services like GitHub and an increased adoption of distributed SCM systems will dramatically change open source development work flows on teams of all sizes in addition to changing the way individual developers work 110 Commands Overview This section is meant to be a really quick reference to the commands we have reviewed in Git and a quick description of what they do where we have talked about them and where to find out more infor mation on them Basic Git git config http www kernel org pub software scm git docs git config html Sets configuration values for things like your user name email and gpg key your preferred diff algorithm file formats to use proxies remotes and tons of other stuff For a full list see the git config docs http www kernel org pub software scm git docs git config html git init http www kernel org pub software scm git docs git init html Initializes a git repository creates the initial git directory in a new or existing project git clone http www kernel org pub software scm git docs git clone html Copies a Git repository from another place and adds the original location as a r
48. er if your project needs to remain private GitHub hosts many popular projects featured in the PeepCode series including Ruby on Rails http github com rails rails tree master Merb http github com wycats merb core tree master RSpec http github com dchelimsky rspec tree master and Capistrano http github com jamis capist rano tree master GitHub GitHub is interesting as a source code hosting service because it 107 includes some social networking features which is not what most people imagine when they think of hosting source code You can follow friends other developers or just individual projects You then subscribe to a single Atom feed and are kept up to date on what all those projects and people are doing code wise e hub schacon account I profile guides I log out git mo repositories all search News Feed Your Repositories create a new one all public private sources forks for you I from you git ruby dkubb committed to dm core about 5 hours ago B 8575b5720131d9e3b83cfffb3d5cd689410017bb git source Added argument checking to Association initializers ruby git dkubb committed to dm core about 5 hours ago ticgit B 4e9199b2573bebae2e1 7feee93b43176a3c601a Switched yo using yield instead of block call when possible dkubb committed to dm core about 6 hours ago 946dc8 183159ae5cl6IbOSe6d2522ae81a52594 Removed method accidentally added during merge conflict resolution dkubb committe
49. fie Df exact Al fields gone O Pateh O Tree Ditt Old version QNew version Lines of context e Agnore space change Comments Author Linus Torvalds lt torveldstype 70 osdl org 2005 04 07 15 19 Comitter Linus Torvalds lt torval stype 70 csdl org 2005 04 07 a B n i copy Branahas IINA PIUNE PYS IOP BALTA Tenotes githeo plths remotes itha github sys log rates or Follows Precedes 10 99 Initiol vevisien ef gie the informatica soneger from bell Gitk will also take most of the same arguments that git log will take including since until max count revision ranges and path limit ers One of the most interesting visualizations that regularly use is gitk all which will show all of your branches next to each other rather than just the one you are currently on INSTAWEB If you don t want to fire up Tk you can also browse your repository quickly via the git instaweb command This will basically fire up a web server running the gitweb http git or cz gitwiki Gitweb CGI script using lighttpd apache or webrick It then tries to automatically fire up your default web browser and points it at the new server git instaweb httpd webrick 2008 04 08 20 32 29 INFO WEBrick 1 3 1 2008 04 08 20 32 29 INFO ruby 1 8 4 2005 12 24 i686 darwin8 8 2 69 000 127 0 0 1 Git git summary alejke htp 127 0 0 1 1234 7p git a summary RSS projects git summary m com
50. flict in Rakefile Automatic merge failed fix conflicts and then commit the result It tells us that there was a conflict and so the new commit object was not created We will have to merge the conflicted file manually and then commit it again The output tells us the files that had conflicts in this case it was the Rakefile rakefile rb spec Gem Specification new do s s platform Gem Platform RUBY s name simplegit lt lt lt lt lt lt lt HEAD Rakefile s version 0 1 2 s version 0 2 0 gt gt gt gt gt gt gt versioning Rakefile s author Scott Chacon s email schacon gmail com s summary A simple gem for using Git in Ruby code s files FileList lib to_a s require path lib end 78 We can see that in the master branch the version was changed to 0 1 2 and in the versioning branch the same line was changed to 0 2 0 All we have to do is choose which one is correct and remove the rest of the lines like so rakefile post rb spec Gem Specification new do s s platform Gem Platform RUBY s name simplegit s version 0 2 0 s author Scott Chacon s email schacon gmail com s summary A simple gem for using Git in Ruby code s files FileList lib to_a s require path lib end Now we add and commit that file and we re good git add Rakefile git commit m fixed co
51. g The Treeish The Git Directory Working Directory The Index Non SCM Uses of Git 54 54 55 ST 63 65 1 2 75 ae 80 86 89 91 92 94 Using Git Setting Up Your Profile Getting a Git Repository Normal Workflow Examples Log the Commit History Browsing Git Searching Git Git Diff Branching Simple Merging Rebasing Stashing Tagging Exporting Git The Care and Feeding of Git Distributed Workflow Examples 105 Sharing Repositories 10 7 Hosted Repositories 11 Commands Overview 111 Basic Git 115 Inspecting Repositories 17 Extra Tools 119 References and Endnotes 119 Web Documentation 120 Screencasts About this book It took me a pretty long time to really get Git As I ve continued to use Git more and more where work I ve found myself trying to teach people what it is and why we use it over and over again and the reality is that Git generally has a pretty steep learning curve compared to many other systems I ve seen case after case of devel opers who love Git after they finally understand it but getting to that point is often somewhat painstaking This book is aimed at the developer who does not particularly like Subversion Perforce or whatever SCM system they are currently using has heard good things about Git but doesn t know where to start or why it s so wonderful It is meant to explain Git as simply as possible in a clean concise easily readable volume My goal is to help you unde
52. git grep L v git v1 5 3 8 v1 0 0 v1 5 3 8 contrib fast import git p4 bat v1 5 3 8 contrib p4import README v1 5 3 8 t t5100 patch0007 v1 5 3 8 t t5100 patch0008 v1 5 3 8 templates this description v1 0 0 debian git arch files v1 0 0 debian git cvs files v1 0 0 debian git doc files v1 0 0 debian git email files v1 0 0 debian git svn files v1 0 0 debian git tk files v1 0 0 templates this description e git grep http www kernel org pub software scm git docs git grep html Git Diff Git has a great diff utility built in that can give you statistics or a patch file given any combination of tree objects working directory and index 72 Two common uses of this include seeing what you ve worked on but not committed yet and creating a patch file to send to someone over email though there is a much preferred way to share changes which we will learn about in the distributed workflow section a bit later What has changed If you simply run git diff with no arguments it will show you the dif ferences between your current working directory and your index that is the last time you ran git add on your files For example if add my email to the README file and run it will see this git diff diff git a README b README index 569b350 26c6ac8 100644 a README b README 5 4 5 4 This library calls git commands and returns the output It is an example for the Git Peepcode book
53. hanges are fetched from developers by lieutenants responsible for specific subsystems and merged and tested Lieutenant branches are then fetched by the dictator and merged and pushed into the blessed repository where the cycle starts over again developer developer developer developer FIG L Approved features gradually make their way up the ladder This is a model something like the Linux kernel uses Linus being the benevolent dictator This model is much better for large teams and can be implemented with multiple and varied levels of lieutenants and sub lieutenants in charge of various subsystems At any stage in this process patches or commits can be rejected not merged in and sent up the chain INTEGRATION MANAGER MODEL This is where each developer has a public repository but one is considered the official repository it is used to create the pack 103 ages and binaries A person or core team has commit rights to it but many other developers have public forks of that repository When they have changes they issue a pull request to an integration man ager who adds them as a remote if they haven t already then merges tests accepts and pushes developer developer developer public public public FIG M Private and public repositories driven by read only pull requests This is largely how community based git repositories like GitHub were built to work and how many smaller open source projects oper ate
54. he changes i C2 between Commit o and 2 CONCIS y Commit 1 to the files in i Remote Commit 1 creating a z master new Commit 2 Then as you ll remember you and Jen both commit again You ll notice that now it looks like she cloned you and committed and then you changed that code rather than you both working at the same time and merging 36 At this point instead of merging two more times like we did originally we rebase the next two commits she makes 37 jen master t Rl lt R2 lt R3 a co Soi Mook Scat o Gee master And finally we are left with a commit history that looks like Figure 1 rather than Figure 2 which is what we would have if we had merged instead 1 R1 lt R2 lt R3 ra co C6 lt C7 Rl lt R2 lt e R3 2 ee co ci i You should remember to only do this on local branches before you push or on repositories that nobody has fetch access to if anyone pulls down the objects that will become abandoned during a rebase it gets a bit frustrating 38 Use Cases So why is this helpful exactly It means that you can keep your development cycles loosely coupled Here is an example of a com mon workflow with cheap branches You have a master branch that is always stable you never merge anything into it that you wouldn t put into production Then you have a development branch that you merge any experimental code into bef
55. hing Git does is create a Git directory This is the directory that stores all the object data tags branches hooks and more Everything that Git permanently stores goes in this single directory When you clone someone else s reposi tory it basically just copies the contents of this directory to your computer Without a checkout called a working directory this is called a bare Git repo and moving it to another computer backs up your entire project history It is the soul of Git When you run git init to initialize your repository the Git directory is by default installed in the directory you are currently in as git This can be overridden with the G T_DIR environment variable at any time In fact the Git directory does not need to be in your source tree at all It s perfectly acceptable to keep all your Git directories in a central place ex opt git myproject git and just make sure to set the GIT_DIR variable when you switch projects you are working on ex home username projects myproject The Git directory for our little project looks something like this HEAD config hooks post commit pre commit index info 44 z exclude bjects 05 76fac355dd17e39fd2671b010e36299f713b4d Oc 819c497e4eca8e08422e61ladec781cc91d125d la 738da87a85f2b1c49c1421041cf41d1d90d434 AT 6340d6459e05787f644c2447d2595f5d3a54b 99 fla6d12cb4b6f19c8655fca46c3ecf317074e0
56. hot commit commitdi tree snapshot commit commitgiff tree snapshot commit commitdit tree snapshot commit commitditi tree snapshot commit commitdit tree snapshot commit commitditt tree snapshot commit commitdiff tree snapshot commit commitdiff tree snapshot commit commitait tree snapshot commit commicit tree snapshot commit commitdif tree snapshot commit committi tree snapshot commit commicitt tree snapshot commit commitdift tree snapshot commit commitaitf tree snapshot When you are done you can run the following to shut down the server git instaweb stop This is a quick way to throw up a web interface on your git repository alee 70 for sharing with others or simply browsing it in a different way For a more long term web interface to your repository you can put the gitweb Perl files that come with Git into your cgi bin directory e git show http www kernel org pub software scm git docs git show html e git Is tree http www kernel org pub software scm git docs git Is tree html e git cat file http www kernel org pub software scm git docs git cat file html e gitk http www kernel org pub software scm git docs gitk html e git instaweb http www kernel org pub software scm git docs git instaweb html Searching Git Git has an easy way for searching through trees in your repository withou
57. html Runs a git fetch then a git merge git push http www kernel org pub 114 software scm git docs git push html Pushes all the objects that you have that a remote version does not yet have to that repository and advances its branches git remote http www kernel org pub software scm git docs git remote html Lists all the remote versions of your repository or can be used to add and delete them Inspecting Repositories git log http www kernel org pub software scm git docs git log html Shows a listing of commits on a branch or involving a specific file and optionally details about what changed between it and its par ents git show http www kernel org pub software scm git docs git show html Shows information about a git object normally used to view commit information git Is tree http www kernel org pub software scm git docs git ls tree html 115 Shows a tree object including the mode and name of each node and the SHA 1 value of the blob or tree that it points to Can also be run recursively to see all subtrees as well git cat file htto www kernel org pub software scm git docs git cat file html Used to view the type of an object if you only have the SHA 1 value or used to redirect contents of files or view raw information about any object git grep http www kernel org pub software scm git docs git grep html Lets you search through your trees of content for w
58. ibutors as a remote and try out their branches before deciding to merge them in If it breaks things or is not a good patch you simply delete the merge feature branch and that s it Local uncommitted changes not checked in to index merged alex remotes alex prettier search results page remove dependency on ultraviolet and code highlighting edit in place thanks jQuery massive reorganization no README no line numbers fix up style and layout more to be done Merge git github com schacon git wiki into rubygit Merge git github com schacon git wiki into ruby todo entry textilify README cleaning up and added back in the delete link remotes origi added search through added remote branch support you could fetch s added patch file download you can now add commit messages to each save Merge commit alex master update todo fix route duplication FIG J Project collaboration using multiple branch forks and merges A common problem with open source projects managed with Subversion is that a patch is sent which was made against and older version of the code base With Git it s as easy as applying the outdated patch in a new branch then rebasing from master to bring it up to date with the current code base You branch and rebase or merge several times a day in and out of several different branches some of which last for hours and some are continually there Once you get used to this pattern it complete
59. ile gt ommitted to update what will be modified README modified Lib simplegit rb HHRHHO HHH HHH You can see that if we commit at this point only the Rakefile will show up as changed in the commit 58 acd E git commit o If we want to commit all our changes we can use this shorthand which will automatically run a git add on every modified file to our index then commit the whole thing git commit a m committing all changes If you would like to give a more useful commit message you can leave out the m option That will fire up your EDITOR to add your commit message Give special care to the first line of your commit message it will often be the only thing people see when they are looking through your commit history Now we can continue this loop modifying adding and committing during our development e git status http www kernel org pub software scm git docs git status html 59 Interactive Adding Although that will work for all of your development needs many developers simply use a nearly every time they commit to just automatically add everything to the index there is another way of adding files that makes for a more controlled and thematic set of commits This is called interactive adding and it is a very powerful tool to controlling what goes into each commit Let s say we add a new function to our Lib simplegit rb file add a new task to our Rakefile and the
60. implegit rb 4 1 files changed 4 insertions deletions git stash show stash 2 lib simplegit rb 8 1 files changed 8 insertions deletions 87 can also use any normal git tools that will take a tree on it for instance git diff git diff stash 1 diff git a lib simplegit rb b lib simplegit rb index e939f77 b03bc9c 100644 a lib simplegit rb b lib simplegit rb 21 10 21 6 class SimpleGit command git ls tree r t treeish end def commit message commit message command git commit m message end private def command git_cmd And finally can apply it git stash apply stash 1 On branch master Changed but not updated use git add lt file gt to update what will be committed modified lib simplegit rb no changes added to commit use git add and or git commit a Now we can see that our working directory is back to where it was with one file in an unstaged state Now would have to git add and git commit it if wanted to keep the change Normally it s not even this complicated If you run git stash apply 88 without the actual stash reference it will just apply the last stash you saved on that branch Normally will just use git stash to save something go work elsewhere then come back and run git stash apply to get back to where w
61. ion of a project they store the code delta or diff When Git stores a new version of a project it stores a new tree a bunch of blobs of content and a collection of point ers that can be expanded back out into a full directory of files and subdirectories If you want a diff between two versions it doesn t add up all the deltas it simply looks at the two trees and runs a new diff on them This is what fundamentally allows the system to be easily distributed it doesn t have issues figuring out how to apply a complex series of deltas it simply transfers all the directories and content that one user has and another does not have but is requesting It is efficient about it it only stores identical files and directories once and it can com press and transfer its content using delta compressed packfiles but in concept it is a very simple beast Git is at it s heart very stupid simple Focus and Design There are a number of areas that the developers of Git including and especially Linus have focused on in conceiving and building Git There may be a lot of things that Git is not good at but these things are what Git is very good at 11 Non Linear Development Git is optimized for cheap and efficient branching and merging It is built to be worked on simultaneously by many people having mul tiple branches developed by individual developers being merged branched and re merged constantly Because of this branching is incredib
62. it s recommended to use the SSH protocol Many reposito ries like GitHub have SSH enabled for account owners to push over and git daemon enabled for the public to pull over which is often the most efficient combination e git daemon http www kernel org pub software scm git docs git daemon html Over SSH Git can work entirely over SSH it actually does much the same thing that happens over the git protocol except it implicitly has authentication built in If a user has SSH and write access to the repo 105 and its subdirectories then that user can push over SSH as well git clone bare scp r project bare user host repos project git git clone user host repos project git Git ships with the git shell a slightly more secure shell that restricts the user to performing only Git related actions If you use SSH public keys you won t need to give out any passwords of create user accounts for other developers who need to have write access to the repository However the restricted git user needs to have write access to the files and directories in the repository which can be slightly awkward to setup and maintain Over HTTP This is pretty easy to setup because there is no requirement other than a static web server it is not like SVN which requires a DAV server to run If you want to push over http however you will need DAV setup it s generally a much better idea to use SSH to do so however The only caveat
63. it README simplegit Rakefile simplegit TODO simplegit lib simplegit lib simplegit rb You can also archive parts of your project This command will create a zip file of just the lib directory of the first parent of your master branch that will expand out into the current directory git archive format zip master lib gt simple git lib zip Which will unzip like this unzip simple git lib zip Archive simple git lib zip ce9b0d5551762048735dd67917046b44176317e0 creating lib inflating lib simplegit rb e git archive http www kernel org pub software scm git docs git archive html The Care and Feeding of Git Git requires a bit of tender loving care from time to time It may seem a bit odd but occasionally you should run a few commands on your repositories to make sure they re healthy and running as quickly as possible 92 garbage collection The git gc command is an important one to remember It will pack up your objects into the delta compressed format saving you a lot of space and seriously speeding up several commands git gc Generating pack Done counting 91 objects Deltifying 91 objects 100 91 91 done Writing 91 objects 100 91 91 done Total 91 delta 33 reused 0 delta 0 Pack pack 9ca918b18abca509b2de71439522a62178415ebd created Removing unused objects 100 Done If can turn gc ing automatically on and off by setting a configuration setting to 1 or o git c
64. it gets only the files it does not already have in a delta compressed package and then expands them locally Log and status files could even be transferred back by a push An example of a media company actually using this approach is Reactrix http reactrix com which also happens to be where work 50 Somewhat interestingly Git being a good solution to this problem is what exposed me to the tool in the first place We were using Git for content distribution on our network since the 1 0 release back in 2005 but using Perforce for version control internally It wasn t until nearly a year later that we switched to actually using it to manage our source code Distributed Document Oriented Database Using Git as a backend for a document oriented database could have some interesting applications Git provides a number of features such as replication searching with grep and full versioning history for free DISTRIBUTED WIKI Suppose we wanted to have a wiki for documentation on a project If we create a wiki that works on files we can simply write those files into a Git repository and run a commit after every change This gives us good performance since it s just reading the content off the disk We also get full file version history and easy recently changed data Searching is built in and we can edit the wiki offline The other cool feature we could use is the distributed nature of Git We could add other people on the pro
65. ject as remote repositories and push to and fetch from them merging changes to write a book or documentation collaboratively We could branch to try out a re write and then either merge it in or throw it away if we don t like it We could send a pull request to our colleagues for them to try out the branch to preview it before we decide whether to merge it in or not It s possible the entire wiki project could even live in a bare branch that is a branch with no common ancestors with any existing branch in the same repository as our project so clones can get the documentation as well without it muddying up our code tree See the git wiki http github com al3x git wiki tree master project for an example of this DISTRIBUTED ISSUE TRACKER Another similar project might be a distributed ticketing system where all the tickets bugs and features for a project could be stored in a Git repository worked on offline and transferred with a project Examples of projects trying to do this are Ditz http ditz rubyforge org Kipling http gitorious org projects kipling and my own TicGit http github com schacon ticgit wikis Backup Tool Let s suppose that you want to build something like a distributed Time Machine backup system Apple all rights reserved that efficiently packs up its backups and transfers them to multiple machines l m hoping by now that you could see the benefits of using the Git toolkit to accomplish this b
66. ly changes the way you approach your development and the way you 40 contribute and collaborate The Treeish Besides branch heads there are a number of shorthand ways to refer to particular objects in the Git data store These are often referred to as a treeish Any Git command that takes an object be it a commit tree or blob as an argument can take one of these shorthand versions as well will list here the most common but please read the rev parse com mand http www kernel org pub software scm git docs git rev parse html for full descriptions of all the available syntaxes FULL SHA 1 dae86e1950b1277e545cee180551750029cfe735 You can always list out the entire SHA 1 value of the object to refer ence it This is sometimes easy if you re copying and pasting values from a tree listing or some other command PARTIAL SHA 1 dae86e Just about anything you can reference with the full SHA 1 can be referenced fine with the first 6 or 7 characters Even though the SHA 1 is always 40 characters long it s very uncommon for more than the first few to actually be the same Git is smart enough to figure out a partial SHA 1 as long as it s unique 41 BRANCH OR TAG NAME master Anything in git refs heads or git refs tags can be used to refer to the commit it points to DATE SPEC master yesterday master 1 month ago This example would refer to the value of that branch yesterday Importantly this is the value of
67. ly cheap and merging is incredibly easy Distributed Development Git is built to make distributed development simple No repository is special or central in Git each clone is basically equal and could generally replace any other one at any time It works completely offline or with hundreds of remote repositories that can push to and or fetch from each other over several simple and standard protocols Efficiency Git is very efficient Compared to many popular SCM systems it seems downright unbelievably fast Most operations are local which reduces unnecessary network overhead Repositories are generally packed very efficiently which often leads to surprisingly small repo sizes The Ruby on Rails Git repository download which includes the full history of the project every version of every file weighs in at around 13M which is not even twice the size of a single checkout of the project 9M The Subversion server repository for the same project is about 115M Git also is efficient in its network operations the common Git trans fer protocols transfer only packed versions of only the objects that have changed It also won t try to transfer content twice so if you 12 have the same file under two different names it will only transfer the content once A Toolkit Design Git is not really a single binary but a collection of dozens of small specialized programs which is sometimes annoying to people trying to learn Git
68. mes It demonstrates the branch and show branch commands how to switch branches how to stash changes how to list and apply stashes how to resolve conflicts how to create and delete topic branches and what fast for ward merges are 75 git you want to create it by passing the b flag git checkout b newfunc Now to check which branch we are on we just type git branch git branch master newfunc We can see we are now on our new branch This means that if we modify a file and commit it this branch will include that change but the master branch will not have it yet So we add a new method to our library and commit it vim lib simplegit rb git commit a m added lstree function Created commit la8c32e added lstree function 1 files changed 4 insertions deletions Now we want to change something in the README in the master branch but we haven t tested this function yet so we don t want to merge our new branch in yet That s fine we just switch back and make the change git checkout master vim README add some text git commit a m added more description Created commit d6fad7d added more description 1 files changed 1 insertions 1 deletions Now lets see what the differences in our branches are 76 git diff stat master newfunc README Apes lib simplegit rb 4 2 files changed 6 insertions 2 deletions We could also get a p
69. mit 189 search Ore summary shortlog log commit commitdiff tree description owner last change shortlog tags Unnamed repository edit this file to name it for gitweb Scott Chacon Sat 8 Mar 2008 06 43 46 0000 Junio C Hamano Junio C Hamano Junio C Hamano Junio C Hamano Junio C Hamano Pierre Habouzit Junio C Hamano Uwe Kleine Junio C Hamano Junio C Hamano Junio C Hamano Alex Riesen Christian Couder SZEDER Gabor SZEDER Gabor Charles Bailey Merge branch maint master scott orgivHEAD _criginimaster send email no signed off cc should suppress sob cc Merge branch js reflog delete Merge branch dc format pretty Merge branch cb mergetool unquote_c_style fix off by one origin maint test lib fix TERM to dumb for test repeatability config txt refer to upload pack and receive pack Merge branch ar sgid bsd Merge branch cc run command Merge branch maint of git repo or cz git gui into Do not use GUID on dir in git init shared all on run command Redirect stderr to a pipe before redirecti bash git branch d and m lists only local branches bash add git branch options Add a very basic test script for git mergetool 5 weeks ago gitgui 0 9 3 git gui 0 9 9 18 commit shortlog log 6 weeks ago 1 5 4 3 7 weeks ago v1 5 4 2 GIT 1 5 4 3 189 commit shortlog log GIT 1 5 4 2 189 commi shortlog log commit commitgitf tree snaps
70. more information on available configuration options git index This is the default location of the index file for your Git project This location can be overridden with the GIT_INDEX environment variable which is sometimes useful for temporary tree operations See the chapter on the Git Index for more information on what this file is used for git objects 46 This is the main directory that holds the data of your Git objects that is all the contents of the files you have ever checked in plus your commit tree and tag objects The files are stored by their SHA 1 values The first two characters make up the subdirectory and the last 38 is the filename For exam ple if the SHA 1 for a blob we ve checked in was a576fac355dd17e39fd2671b010e36299f713b4d the file we would find the Zlib compressed contents in is GIT DIR objects a5 76fac355dd17e39fd2671b010e36299F713b4d git refs This directory normally has three subdirectories in it heads remotes and tags Each of these directories will hold files that cor respond to your local branches remote branches and tags respec tively For example if you create a development branch the file git refs heads development will be created and will contain the SHA 1 of the commit that is the latest commit of that branch git HEAD This file holds a reference to the branch you are currently on This basically tells Git what to use as the parent of your next commit Th
71. n add a new TODO file to our proj ect Later we come back and want to commit but we don t remem ber which files had to do with each other and we don t just want to commit them all together because that s confusing for collaborators trying to review our code Interactive mode lets us modify our index interactively before committing To fire it up type git add i git add i staged unstaged path 1 unchanged 5 Rakefile 2 unchanged 4 0 lib simplegit rb Commands 1 status 2 update 3 revert 4 add untracked 5 patch 6 diff 7 quit 8 help What now gt We can see that we have two files that are being tracked have been added at some point in the past that have been modified We can not yet see our new TODO file though To add that type 4 for the add untracked option and hit Enter What now gt 4 1 TODO Add untracked gt gt 1 1 TODO INTERACTIVE ADD SCREENCAST The next screencast is Interactive Add in Git which demonstrates how to use the git add interactive command It covers all of the major features of interactive adding including status update revert add untracked patch and diff 60 Add untracked gt gt added one path Commands 1 status 2 update 3 revert 4 add untracked 5 patch 6 diff 7 quit 8 help What now gt You will see all the untracked files in your working directory Type the numbers of the files you want to add or a range i e 1 5 and hit ente
72. nflict Created commit 47c668a fixed conflict Undoing a Merge Assume we have gone through some massive merge because some one on your team hasn t committed in a while or you have a branch that was created some time ago but hasn t been rebasing and you want to pull it in So you try to git merge old branch it and you get conflict after conflict and it is just too much trouble to deal with and you just want to undo it all This is where git reset comes in To reset your working directory and index back to what it was before you tried the merge simply run 79 git reset hard HEAD The hard makes sure both your index file and working directory are changed to match what it used it be By default it will only reset your index leaving the partially merged files in your working direc tory If you happen to have worked through it all and committed then decided that it was a mistake because all of your tests break or something you can still go back and throw away that commit by running git reset hard ORIG HEAD This is only helpful if you want to undo the latest change or changes If you happen to commit again then decide that you want to keep the latest commit but undo a commit that was added sometime before that you ll need to use git revert which is a bit too danger ous to cover here e git branch http www kernel org pub software scm git docs git branch html e git merge http www kernel org pub software scm
73. ny object in any reachable branch git daemon http www kernel org pub software scm git docs git daemon html Runs a simple unauthenticated wrapper on the git upload pack pro gram used to provide efficient anonymous and unencrypted fetch access to a Git repository 118 References and Endnotes Here are some references that used or that you may use to find out more about Git The example git repository that was working with throughout this book can be cloned from its GitHub repository http github com schacon simplegit For anything you cannot find in this book or these references be sure to ask the fantastic people hanging out at the git channel on irc freenode net Web Documentation Main Git Documentation http www kernel org pub software scm git docs fantastic reference for all the command line programs Git User s Manual http www kernel org pub software scm git docs user manual html Git for Computer Scientists http eagain net articles git for computer scien tists good detail about the DAG object model A Tutorial Introduction to Git http www kernel org pub software scm git docs tutorial html Git Rebase Explained http wincent com knowledge base Git_rebase_explained A Tour of Git the Basics http cworth org hgbook git tour Junio Hamano New Git Maintainer http kerneltrap org node 5496 119 some history on git and Junio becoming the new maintainer Screencasts
74. o my lib simplegit rb file but it s not complete git status On branch master Changed but not updated use git add lt file gt to update what will be committed modified Llib simplegit rb no changes added to commit use git add and or git commit a git stash 86 Saved working directory and index state WIP on master c1l0d7f made the ls tree function recursive and list trees To restore them type git stash apply HEAD is now at c110d7f made the 1ls tree function recursive and list trees git status On branch master nothing to commit working directory clean Now can see that my working directory is clean as if had commit ted but did not Now can switch branches work for a while some where else then switch back So where did that change go How do get it back Well can see my stashes by running git stash list git stash list stash 0 WIP on experiment 89e6d12 trying git archive stash 1 WIP on master c110d7f made the ls tree function recursive stash 2 WIP on master c110d7f made the ls tree function recursive see have two stashes on the master branch both saved off of working from the same commit and have one stashed change off the experiment branch However can t remember which stash was the one want so can use git stash show to figure it out git stash show stash 1 lib s
75. om in this case one for every developer with a public fork of that project that might push changes care to try 99 nick s computer private repo push public fetch origin ssh nickh hengeveld com git ticgit git ssh git github com schacon ticgit git fetch nick push github private repo add amp commit working directory my computer 100 You can also remove remotes at any time which simply removes the lines that contain the URL in your git config file and the references to their remote branches in git refs remote name directory It will not remove any of the git objects so if you decide to add it again and fetch very little will be transferred You can also view useful information about a remote branch by using the remote show command For example if run this on a checkout of the Git source code itself will see this git remote show origin remote origin URL git git kernel org pub scm git git git Remote branch es merged with git pull while on branch master master Stale tracking branches in remotes origin use git remote prune old next Tracked remote branches html maint man master next pu todo git remote http www kernel org pub software scm git docs git remote html Possible Workflows The idea of having multiple remote repositories that you can push to and or pull from is probably new to you and many people have a hard time figuring out what their workflow
76. onfig global gc auto 1 This will make git automatically gc itself occasionally You may want to setup a cron to do this at night however as it can take a while sometimes on really large repositories fsck and prune If you want to check the health of your repository you can run git fsck which will tell you if you have any unreachable or corrupted objects in your database and help you fix them git fsck dangling tree 8276318347b8e971733ca5fab77c8f5018c75261 dangling blob 2302a5a4baec369fb631bb89cfe287cc002dc049 93 dangling blob cb54512d0a989dcfb2d78a7 f3c8909f76ad2326a dangling tree 8e1088elcclbc67e0ef01e018707dcb07a2a562b dangling blob 5e069ed35afae29015b6622fe715c0aeel10112ad Which you can then remove with git prune you can run it with n first to see what it will do git prune n 2302a5a4baec369fb631bb89c fe287cc002dc049 blob 5e069ed35afae29015b6622fe715cOaeel0112ad blob 8276318347b8e971733ca5fab77c8f5018c75261 tree 8e1088elccl1bc67e0ef01e018707dcb07a2a562b tree cb54512d0a989dc fb2d78a7 f3c8909Ff76ad2326a blob git prune git fsck e git gc http www kernel org pub software scm git docs git gc html e git fsck http www kernel org pub software scm git docs git fsck html e git prune http www kernel org pub software scm git docs git prune html Distributed Workflow Examples Now we ve gone over most of the basic commands that you ll use on a day to day basis as a single developer This ch
77. opped providing a free version of its tool to the open source community because they felt some developers had reverse engineered it in violation of the license Since Linus had and still has a passionate dislike of just about all existing source code management systems he decided to write his own Thus in April of 2005 Git was born A few months later in July maintenance was turned over to Junio Hamano who has maintained the project ever since I m an egotistical bastard and name all my projects after myself First Linux now git Linus Git started out as a collection of lower level functions used in various combinations by shell and perl scripts Recently since 1 0 more and more of the scripts have been re written in C referred to as built ins increasing portability and speed Though originally used for just the Linux kernel the Git project spread rapidly and quickly became used to manage a number of other Linux projects such as the X org Mesa3D Wine Fedora and Samba projects Recently it has begun to spread outside the Linux world to manage projects such as Rubinius Merb Ruby on Rails Nu lo and many more major open source projects Understanding Git In this section we will go over what Git was built for and how it works hopefully laying the groundwork to properly understand what it is doing when we run the commands The first commit message for the Git project was initial version of git
78. ords and phrases without having to actually check them out git diff http www kernel org pub software scm git docs git diff html Generates patch files or statistics of differences between paths or files in your git repository or your index or your working directory gitk http www kernel org pub software scm git docs gitk html Graphical Tcl Tk based interface to a local Git repository git instaweb http www kernel org pub 116 software scm git docs git instaweb html Wrapper script to quickly run a web server with an interface into your repository and automatically directs a web browser to it Extra Tools git archive http www kernel org pub software scm git docs git archive html Creates a tar or zip file of the contents of a single tree from your repository Easiest way to export a snapshot of content from your repository git gc http www kernel org pub software scm git docs git gc html Garbage collector for your repository Packs all your loose objects for space and speed efficiency and optionally removes unreachable objects as well Should be run occasionally on each of your repos git fsck http www kernel org pub software scm git docs git fsck html Does an integrity check of the Git filesystem identifying dangling pointers and corrupted objects git prune http www kernel org pub software scm git docs git prune html 117 Removes objects that are no longer pointed to by a
79. ore you imagine pulling it into the master branch It s a common error to think of the master branch as being equivalent to Subversion s trunk However a custom development branch is much closer in practice to the Subversion trunk where experimental work is done You create a new branch each time you begin to work on a story or feature branching it off your current development branch each time so if you get blocked and need to put it on hold it doesn t effect anything else When you do get back to them you rebase them to the current development and it is just like you started from there Often times you merge the branch back into development and delete it the same day that you created it If you get a huge project or idea say refactoring the entire code base to the newest version of your framework or switching database vendors or something you create a long term branch continuously rebase it to keep it in line with other development and once every thing is tested and ready merge it in with your master Working with others is unbelievably easy You ask in an IRC room if someone has implemented a feature in a library you are using Turns out that someone has and you are sent the URL of their public Git repo for that project You add it as a remote fetch it create a new merge feature branch off your development branch merge in the new 39 changes and you re done There s no awkward emailing of patches you can just add contr
80. press vrernals Source code control and beyond by Scott Chacon Git Internals 2008 Scott Chacon Every effort was made to provide accurate information in this document However neither Scott Chacon nor Topfunky Corporation shall have any liability for any errors in the code or descriptions presented in this book This document is available for US 9 at PeepCode com http peepcode com Group discounts and site licenses can also be purchased by sending email to peepcode topfunky com OTHER PEEPCODE PRODUCTS e RSpec http peepcode com products rspec basics A three part series on the popular behavior driven development frame work e Rails from Scratch http peepcode com Learn Rails e RESTful Rails http peepcode com products restful rails Teaches the concepts of application design with REST e Subscription pack of 10 http peepcode com products subscription pack of 10 Save money Buy 10 PeepCode credits e Javascript with Prototype http peepcode com products javascript with prototypejs Code confidently with Javascript e Rails Code Review PDF http peepcode com products draft rails code review pdf Common mistakes in Rails applications and how to fix them oO N WD WO About this book Installing Git Installing on Linux Installing on Mac Windows A Short History of Git Understanding Git What is Git Focus and Design Git Object Types The Git Data Model Branching and Mergin
81. r twice when you re done This will drop you back to the main menu You can then type 1 to see what your index looks like now What now gt 1 staged unstaged path 1 unchanged 5 Rakefile 2 5 0 nothing TODO 3 unchanged 4 0 lib simplegit rb You can see that the TODO file is now staged in the index but the other two are not Let s add the Rakefile but not the Lib simplegit rb file and commit it To do that we hit 2 which lists the files we can update type 1 and enter to add the Rakefile then hit enter again to go back to the main menu Then we hit 7 to exit and run the git commit command What now gt 2 staged unstaged path 1 unchanged 5 Rakefile 2 unchanged 4 0 lib simplegit rb Update gt gt 1 staged unstaged path 1 unchanged 5 0 Rakefile 2 unchanged 4 0 lib simplegit rb Update gt gt updated one path 61 Commands 1 status 2 update 3 revert 4 add untracked 5 patch 6 diff 7 quit 8 help What now gt 7 Bye git commit m rakefile and todo file added Created commit 4b0780c rakefile and todo file added 2 files changed 9 insertions deletions create mode 100644 TODO The interactive shell is pretty simple and very powerful playing with it instead of running git add commands directly may help in under standing what s happening since you can see the status of your files in the index versus the working directory more clearly It helps visualize that what
82. rstand Git internals as well as usage at a fundamental level by the time you finish this book To accomplish this l m starting the book out after the introduction with a section about what Git actually does rather than how to use it found that didn t really understand Git and had many problems using it until understood what it was actually doing at a low level rather than thinking of it as a different weird SVN like system Installing Git Before we can start playing with Git we ll have to install it I ll quickly cover installing Git on Linux Mac and Windows will not get into really fine detail because others have done that much better but will give you an overview and links as to where to find more detailed instructions on each platform For any of these examples you can find a link to the most current Git source code at git or cz http git or cz would recommend compiling from source if possible simply because Git is lately making big strides in usability so more current versions may be a bit easier to use Installing on Linux If you are installing from source it will go something like the stan dard wget http kernel org pub software scm git git 1 5 4 4 tar bz2 tar jxpvf git 1 5 4 4 tar bz2 cd git 1 5 4 4 make prefix usr all doc info sudo make prefix usr install install doc install info If you are running Ubuntu or another Debian based system you can run apt get git core
83. ry everything is stored perma 48 nently in your Git repository Your working directory is just a copy of a tree so you can edit it and commit changes The Index Git has two places that content states are stored The working direc tory stores one state ata time in a human editable format When committed that state becomes permanent and repeatable by being stored in the object database However how do you determine what changes in your working directory will go into your next commit Per haps you have edited three files and you want two to go into the first commit because they are related changes and the other file into a second commit This is where the index file comes in The index was called the cache for a while because that s largely what it does It is a staging area for changes that are made to files or trees that are not committed to your repository yet It acts as sort of a middle ground between your working directory and your repository When you run git commit the resulting tree and commit object will be built based on the contents of the index Early on the index was called the cache or the current directory cache It is also used to speed up some operations It keeps track of the state of all the files in your working directory so you can quickly see what has been modified since the last commit Non SCM Uses of Git keep saying that Git is primarily a content tracking toolkit with SCM tools built on top of
84. should look like especially if they are moving from a centralized SCM system will present a couple of possible workflows that have seen so you can determine what will work best for you and your team Most of these are simply a matter of convention not even configu ration Each of the models can pretty easily change to another with minimal configuration changes maybe some permissions tweaked 101 here or there CENTRAL REPOSITORY MODEL There is a single repository that all developers push to and pull from developer developer developer developer gt developer developer Ze developer developer FIG K All developers push to a single server This model works just like a centralized SCM and Git can work that way just fine If you setup a repository for your team on a server that everyone has SSH or NFS access to Git can very easily function as a centralized repository This may be common on small teams with non public projects where you don t want to worry about a hierarchy the strength of this model is that it forces everyone to stay up to date with each other and it doesn t depend on a single role Even large teams could use this but in general there are a lot of gains to be made in larger teams with a different or hybrid model 102 DICTATOR AND LIEUTENANT MODEL This is a highly hierarchical model where one individual has com mit rights to a blessed repository that everyone else fetches from C
85. so branched off at one point to try an idea and they named the branch idea locally then pushed that branch We now have access to those changes as origin idea 32 origin idea CR2 origin master n i CR1 lt CR3 lt CR4 a co lt CLl lt CL2 A master We look at the idea branch and like where they re going with it but we also want the changes they ve made on their master branch so we do a 3 way merge of their two branches and our master We don t know how well this is going to work so we make a tryidea branch first and then do the merge there 33 origin idea y CR2 origin master M i CR1 lt CR3 lt CR4 co lt CLI lt CL2 lt CL3 4 4 master tryidea Now we can run our tests and merge everything back into our master branch if we want Then we can tell our friend we cloned from to fetch from our repository where we ve merged their two branches for them and integrated some of our changes as well They can choose to accept or reject that patch Rebasing Let s say you and another developer Jen are working on the same project simultaneously She clones from you and works for a while and commits You have committed in the meantime and want to get your work in sync so you add her repository as the remote jen do a fetch and merge her changes in creating a new merge commit All commits that are simply merges are given
86. st versions of both of them git push scott public Whereas this will only update the master branch git push scott public master In Git the opposite of push is not pull but fetch A pull is a fetch and then a merge e git push http www kernel org pub software scm git docs git push html Multiple Remotes Although a bit different in syntax maybe most of that should seem familiar to any users of other SCM systems However this is where the decentralized part comes in In Git there is really no special repository You can add as many remote repositories that are related 98 to your codebase in some way as you want You can add each of your co workers repositories as read only repositories you can have a centralized one you all share one out on your production servers outside the firewall a public one for stable or sanitized pushes on your personal webserver one on your build server etc etc Pushing to and pulling from multiple sources is easy and straightfor ward You simply add remotes git remote add mycap git github com schacon capistrano git git remote add official git github com jamis capistrano git Then if the the project is updated can pull in the changes from one remote merge them locally and then push to another remote git fetch official git merge official master git push mycap master can also add several remotes to pull and merge fr
87. t having to check them out into your working directory to do it manually It is called git grep and works very much like the tradi tional UNIX grep command with the difference that instead of listing the files you want to search as an argument you list the trees you want to search For example if we wanted to search for the string log_syslog in ver sions 1 0 and 1 5 3 8 of the Git source code in the C files only we can find that very easily git grep n log syslog v1 5 3 8 v1 0 0 c vl 5 3 8 daemon c 16 static int log syslog v1 5 3 8 daemon c 92 if log syslog v1 5 3 8 daemon c 768 if log_syslog v1 5 3 8 daemon c 1055 log_ syslog 1 v1 5 3 8 daemon c 1063 log syslog 1 v1 5 3 8 daemon c 1112 log syslog 1 v1 5 3 8 daemon c 1177 if log syslog v1 0 0 daemon c 13 static int log syslog v1 0 0 daemon c 45 if log syslog v1 0 0 daemon c 423 if log_syslog 71 v1 0 0 daemon c 615 log_ syslog 1 v1 0 0 daemon c 623 log_ syslog 1 v1 0 0 daemon c 653 if log syslog git grep n c log syslog v1 5 3 8 v1 0 0 c v1 5 3 8 daemon c 7 v1 0 0 daemon c 6 You can see that you can view the number of lines that match or the actual lines and you can list as many trees in this case used tags to reference them as you want to search Another interesting example is to see which files in these versions do not contain the string git anywhere in them
88. t repository you will either clone an existing project or you will initialize a new one New Repositories To create a new Git repository somewhere simply go to the directory you want to add version control to and type git init This will create a git directory in your current working directory that is entirely empty If you have existing files you want to add to your new repository type git add git commit m my first commit This will add all of your current files into your new repository and index and then create your first commit object pointing your new master branch to it Congratulations you have now added your source code to Git 55 e git init http www kernel org pub software scm git docs git init html e git commit http www kernel org pub software scm git docs git commit html e git add http www kernel org pub software scm git docs git add html Cloning a Repository Many times you will be cloning a repository however This means that you are creating a complete copy of another repo including all of its history and published branches A clone is for all intents and purposes a full backup If the server that you cloned from has a hard disk failure or something equally catastrophic you can basically take any of the clones and stick it back up there when the server is restored without anyone really the worse for wear In order to do this you simply need a URL that has a Git repository hoste
89. t that branch points to and updates your HEAD to point to this branch now so your next commit will modify it git merge http www kernel org pub software scm git docs git merge html Merges one or more branches into your current branch and auto matically creates a new commit if there are no conflicts git reset http www kernel org pub software scm git docs git reset html Resets your index and working directory to the state of your last commit in the event that something screwed up and you just want to go back git rebase http www kernel org pub software scm git docs git rebase html 113 An alternative to merge that rewrites your commit history to move commits since you branched off to apply to the current head instead A bit dangerous as it discards existing commit objects git stash http www kernel org pub software scm git docs git stash html Temporarily saves changes that you don t want to commit immedi ately for later Can re apply the saved changes at any time git tag http www kernel org pub software scm git docs git tag html Tags a specific commit with a simple human readable handle that never moves git fetch http www kernel org pub software scm git docs git fetch html Fetches all the objects that a remote version of your repository has that you do not yet so you can merge them into yours or simply inspect them git pull http www kernel org pub software scm git docs git pull
90. ubversion as well Mac 10 5 Leopard The easiest way to install is most likely the Git OSX Installer http code google com p git osx installer which you can get from Google Code and has just recently been linked to as the official Mac ver sion on the Git homepage Just download and run the DMG from the website If you want to compile from source all the requirements are installed with the developer CD You can just download the Git source and compile pretty easily if the developer tools are installed Finally MacPorts is also an easy option if you have that installed For an in depth tutorial on installations under Leopard see this article http blog kineticweb com articles 2007 10 30 compiling git for mac os x leopard 10 5 Windows There are two options on Windows currently but the popular one is MSysGit http code google com p msysgit which installs easily and can be run on the Windows command line Simply download the exe file from the downloads list http code google com p msysgit downloads list execute it and follow the on screen instructions A Short History of Git The Git project started with Linus Torvalds scratching the very serious itch of needing a fast efficient and massively distributed source code management system for Linux kernel development The kernel team had moved from a patch emailing system to the proprietary BitkKeeper SCM in 2002 That ended in April 2005 when BitMover st
91. ut this particular problem is interesting because of something that Git doesn t do which is per missions Git stores the mode of its content in the tree but it doesn t store any permissions data which means it s not good for backing up directories in which permissions are important A good example would be the etc directory on a Unix machine One project that has tackled this is Gibak http eigenclass org hiki gibak backup system introduction It implements a metastore in OCaml and it s worth a look if this topic interests you If you are interested in using Git in a non standard way and plan to use Ruby you might be interested in my git gem hitp 52 jointheconversation org rubygit which provides an object oriented interface in Ruby to the Git tools including several of the lower level functions 53 Using Git Now that you hopefully understand what Git is designed to do ata fundamental level how it tracks and stores content how it stores branches and merges and tracks remote copies of the repository let s see how to actually use it This next section presents some of the basic commands that you will need to know in order to use Git effectively At the end of each chapter there will be a link to the official Git doc umentation for each of the commands used in that section in case you want to learn more or see all the options for that command Setting Up Your Profile For every commit you do Git will try to
92. vidual files or we can tell the commit command to automatically add all modified files in our working directory to the index then commit it A good way to find out what you re about to commit that is what is in your index is to use the status command git status NORMAL WORKFLOW SCREENCAST The second screencast we ve provided is Nor mal Workflow in Git which demonstrates how to setup your gitignore file how to use and interpret git status output how to add and remove files from your index how to commit and what git does in the object database dur ing these operations 57 On branch master Changed but not updated use git add lt file gt to update what will be committed modified README modified Rakefile modified Llib simplegit rb no changes added to commit use git add and or git commit a In this example can see that I ve modified three files in my working directory but none of them have been added to the index yet they are not staged and ready to be committed If want to make these changes in two separate commits or have completed work on some of them and would like to push that out can specify which files to add individually and then commit git add Rakefile git status On branch master Changes to be committed use git reset HEAD lt file gt to unstage modified Rakefile Changed but not updated use git add lt f
93. your work ing directory look like the tree that SHA 1 points to and updating the HEAD file so each commit from that point on moves that branch pointer forward in other words it changes the 40 characters in git refs heads current_branch_ name be the SHA 1 of your last com mit 29 Simple Case Now let s see how Git handles pious branen branching fetching and merging l operations abstractly For the following illustrations we will commit represent the entire tree and the commit it points to as a single object tree C1 Suppose that we work on a project h for a while then we get an idea for blob something that may not work out but we want to do a quick proof of concept We create a new branch called experiment off of our main branch which is by conven tion called master We then switch to the new branch and create a few commits master experiment Y co Cl AS C2 lt C3 Then our boss comes in and says we need a hot fix to production So we switch back to our master branch make the change push the release and then tag the new commit with the release number Then we go back to our experiment branch continue working and commit again 30 T1 master CO lt Cl lt C4 KS C2 C3 lt C5 1 experiment At this point we show the new branch code to our co workers and everyone likes the new changes We decide we want to merge them back into our main branch so we

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