Introduction to Bash
Contents
1. home aisha pwd home aisha cslabia home aisha Congratulations We ve learned our first shell command 3 More about your file system In order to explore your file system you ll need to know one command in addition to pwd This command is cd or change directory cd will switch your working directory or current directory to whatever you give it as an argument If you give it no argu ments it will take you to your home directory Keep in mind this command can take either relative or absolute paths An absolute path starts with a slash and is the same regardless of your current directory ex home aisha course A relative path does not begin with a slash and describes a location relative to your current directory ex if your working directory is home aisha the relative path course cs015 would evalute to nome aisha course cs015 You can think of the file system almost like the containment diagrams you made in CS15 Your topmost directory is called the root Each other directory has a parent a directory which contains it and any number of children directories which it contains Each directory on the path is succeeded by a slash Lastly you will often notice that people type commands such as cd or cd Single and double dots are used to signify the current directory and parent directory respectively and represents your home directory home lt login gt Note that some people s paths may2. show up as gpfs main home lt login gt instead of home lt login gt If yours looks like this Introduction to Bash 2015 January 25 2015 2 CS 16 Intro to Algorithms and Data Structures Introduction to Bash 2015 just ignore the first two parts of the path We will explore this some in the next example Now let s practice using cd Enter the following commands and check your output against the provided example Take a look at the diagram provided below the commands and try to follow the file system structure as you go You should end up at the blue highlighted box cslabla home aisha cd cslabia home cd cslabla cd course cslabla course cd cs015 cslabla course cs015 cd cslabla course cd cslabla course q the file system s root your home directory home lt login gt home aisha home lt login gt course 4 Commands for manipulating the file system You should now be in your course directory Let s start by making a directory for cs016 To do this you ll use the program mkdir which takes a single argument the path of the directory to make In most cases you ll be using relative paths so you will only need the Introduction to Bash 2015 January 25 2015 3 CS 16 Intro to Algorithms and Data Structures Introduction to Bash 2015 name of the new directory Before we do this let s try out the first command we saw 1s 1s stands for li
3. 1s command So this command runs 1s on the folder home lt login gt with the a flag set which will display the contents of that folder and include all hidden files We ll learn more about 1s later In the next few steps we ll give you an overview of some useful commands as well as how to use them We ll also go over a brief explanation of the file system For some of you parts of this may be review but you will be expected to know and correctly use these commands in CS16 Additionally this lab goes through essential setup for the upcoming Introduction to Python so please pay close attention and execute all of the commands provided Introduction to Bash 2015 January 25 2015 1 CS 16 Intro to Algorithms and Data Structures Introduction to Bash 2015 2 Running your first commands First start by opening your terminal You should see something that looks like cslabla home aisha This is called your command line prompt Any commands that you run will go after the You should notice that the first part of this prompt consists of the name of the computer you are on in the Sunlab this is one of cslab 1 9 a h The second part of this prompt shows you which directory you are currently in You can also find your current directory by running pwd which stands for print work ing directory Run this command now Your terminal should look something like this but with your login instead of aisha cslabla
4. CS 16 Intro to Algorithms and Data Structures Introduction to Bash 2015 Introduction to Bash 2015 1 What is Bash Bash or the Bourne Again SHell is a Unix shell which allows users to type commands which are then processed and sent to the operating system This shell is very similar to the one used in Apple computers so if you have a Mac you can most likely run these commands on the terminal on your personal computer as well Commands generally have three parts the name of the program being run flags which change how the program executes or displays information and arguments which can spec ify path of data to work on where to put a result or alter the operation of the program For example in the following command Is a home lt login gt command flag s argument s name we can see all of the parts of a command in action The first thing to note is that all the parts of a command are separated by spaces The shell splits your command into tokens that it can understand almost like how we split a sentence into words 1s is the name of the command a is a flag and home lt login gt is an argument In this example lt login gt would be replaced with your CS department login for example home aisha Flags are generally prefixed by one or two dashes and single character flags can generally be combined for example a 1 becomes al The home lt login gt argument is a file path which is where we want to run the
5. akes two arguments first what to copy and second where to copy it to You ll notice we re using which is a wildcard meaning all In this case using course cs016 asgn intros pythonIntro stencil as our first argument means that we want to copy everything from the stencil directory We use as our second argument because we want to copy everything to our current directory cslabla course cs016 pythonIntro 1s cslabla course cs016 pythonIntro cp course cs016 asgn intros pythonIntro stencil cslabla course cs016 pythonIntro 1s pieCount txt pieCounter py primePrinter py sectionOne py Introduction to Bash 2015 January 25 2015 4 CS 16 Intro to Algorithms and Data Structures Introduction to Bash 2015 We re going to now learn mv which stands for move It is used not only to move files but also to rename files Like cp mv takes two arguments where to move a file or directory from and where to move a file to Now let s move your file test into your pythonIntro folder and then rename it README You are going to need to make a README file for each of your projects which documents design bugs and other things You can learn more about this in the docs and will also hear about them in your project handouts cslabla course cs016 pythonIntro mv test cslabla course cs016 pythonIntro mv test README Last but not least we need to know how to remove any files or directories that we have created b
6. e regular empty file toDelete emptyFile1 y rm remove directory toDelete y cslabla course cs016 pythonIntro You should now be all ready for the Introductoin to Python Please run cs016_bashCheckoff so we know that you ve completed it If you ve set everything up successfully you should get a success message otherwise you should go back through the lab and make sure you have completed all parts of the intro The next few pages include a list of other helpful tips and a detachable bash cheatsheet listing both the commands we have already learned Introduction to Bash 2015 January 25 2015 5 CS 16 Intro to Algorithms and Data Structures Introduction to Bash 2015 as well as some other commands that your TAs thought may be helpful Tip If you ever get confused about a command you can use the man pages effectively a bash user manual by typing man lt command gt where lt command gt is the command you want more information about For example man 1s will tell you about all of the flags you can use to see different sorts of files in a directory Introduction to Bash 2015 January 25 2015 6 CS 16 Intro to Algorithms and Data Structures Introduction to Bash 2015 5 Other helpful tips Adding amp to the end of a command will run it in the background This will mean that your terminal will still be usable when you re running a program ex sublime amp If you forget to add an amp but want
7. st segments but really what it means is show me what is in my working directory Let s try this in our course directory now You should see a folder for each CS course you ve taken you will most likely see something like this cslabia course ls cs015 cslabia course Now let s make our directory cslabla course mkdir cs016 cslabia course We have now made an empty cs016 directory Next we re going to try to give it some children files and or directories to prepare us for the first lab Checkpoint Try moving into your newly made cs016 directory Remember there are two different ways to do this using relative and absolute paths For practice try moving in both ways Now that we re in our cs016 directory let s try making a file We know already that we use mkdir to make a directory To make a file we use the command touch which also takes an argument specifying the path or in most cases the name Let s call this file test Try making the file and then using 1s to make sure that we ve made it correctly cslabia course cs016 touch test cslabla course cs016 1s test cslabla course cs016 Checkpoint Try making a directory called pythonIntro within your cs016 directory and the move into that directory We will use this directory in the Introduction to Python lab Now we ll need to copy the stencil for the python lab into this directory To copy we will use the command cp which t
8. to add it afterwards type ctrl z in your terminal which will pause your program and then type bg to start running it in the background instead Add amp disown to the end of a command makes it so when you close your terminal the program isn t automatically closed ex google chrome amp disown If you re not sure where in a path you re going next or what a file name is as you are typing you can use the tab key to autocomplete or be given a list of possible completions to your command To open a new tab in your terminal type ctrl shift t Introduction to Bash 2015 January 25 2015 7
9. ut no longer want Please DO NOT try any of these until you have read the whole section To do this we use a command called rm or rmdir for directories rm and rmdir take a single argument the file folder to remove There are two flags that are important with rm r and f r means recursive so if you want to remove a directory as well as everything in it you can use rm r lt directory gt Note that you cannot remove a directory that has files subdirectories in it using rmdir which is why we use rm r instead You will also notice once you try these that it will ask you for each file whether you re sure you want to remove the file or directory You will have to type y or yes in order to give it permission to delete In order to override this behavior you can add the f flag to rm for example rm f or rm rf Use this with caution It is really easy to delete everything using these commands and while sunlab consultants can restore your files from 2 hours previous using something called snapshots this can sometimes mean quite a bit of work lost Let s try this out without the f flag to see how it works cslabla course cs016 pythonIntro rm README rm remove regular empty file README y cslabla course cs016 pythonIntro mkdir toDelete cslabla course cs016 pythonIntro touch toDelete emptyFilel cslabla course cs016 pythonIntro rm r toDelete rm descend into directory toDelete y rm remov
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