These pages are meant for students new to the SwatCS computers.

After working through the sections in the Table of Contents on the left, you should feel comfortable using some basic unix commands in the terminal window.

And don’t feel like you have to remember it all after one session. Feel free to return to these pages anytime to refresh or learn more. The more comfortable you are with unix commands in the terminal, the more efficient you will be getting your CS labs done!

New users need to set their initial CS account password. If you haven’t already, go to our self-service password app and click the "Click to Request Reset" link near the bottom of the page. From that link you should be able to set your initial CS password (enter your username, click Request Password Reset, check your Swarthmore email, etc).

If you have any trouble setting your password, see our new user help page for detailed instructions and screenshots.

Once you have your CS account password, you can use ssh to access the CS computers. ssh stands for secure shell, and is a program that encrypts all communication between your home computer and the CS computers. It runs from a terminal window and is probably already installed on your computer (if not, see our remote access help page).

On Macs, search for the Terminal application and start it. On Windows, either search for the PowerShell application or install putty and start it. And try to keep the browser window and the terminal window open and side-by-side for the rest of this tutorial, so you can try out commands as we go!

To use ssh, enter the following command in the Terminal or PowerShell/putty window, replacing username with your username (e.g., csmajor1):

Finally, you should be prompted for your CS password, and, if correct, be logged in to one of our CS computers. Here’s an example of what you might see:

In the above example, the user (csmajor1) is logged in to a computer called macaw. You may get a different computer. Many of our computers have bird names (dodo, loon, hawk, etc). And the macaw[~]$ part is the unix terminal prompt. That’s where we will type all unix commands discussed below.

If you have any trouble getting logged in, or any questions about the CS computers, send us an email at sysadmins @ cs.swarthmore.edu and we will be happy to help you.

Your home directory (some people call them folders) is part of a tree-like structure:

Try this example! And the dollar sign ($) below is just the unix prompt (yours might look slightly different). You don’t type the dollar sign, just everything after the dollar sign.

And when we say "run this command", we mean type it in a terminal window.

The above should display /home/username, where username is your actual CS username (like csmajor1, or aturing7). When you first log in, you are always in your home directory (/home/username).

Try this example, too!. Let’s make a sub-directory called testdir, just for testing:

The mkdir command makes a new directory (there’s no output or anything if the command worked).

In the next few sections we’ll see how to view our files and change into different directories, like the test directory we just made.

We use the cd and pwd commands to change directories and display where we are.

Try this!

The first pwd should display your home directory. Then the change directory (cd) command moves you one level down in the tree, to your newly-created testdir. And the last pwd should display /home/username/testdir.

Users new to UNIX are often confused by paths and directories. A full path lists out all directories, from the root, like /home/csmajor1/cs21/labs/00. You can always use a full path, but it’s sometimes quite long.

What does cd .. do? Try it and see if you can figure out where it puts you in the directory tree (hint: use pwd)!

If you use cd .. enough times, you will get to the root of the directory tree (slash or /):

The ls command is short for list. You can use the ls command to see your files and directories (folders). You can also list out files in another directory using the full path (with the slashes in it — see below).

Try these examples!

The first ls above displays a few files and directories in your home directory. You don’t have much at this point (I think it just shows testdir, Desktop, and Documents).

The second ls above displays everything in your testdir directory, which is nothing at this point, since we just made that. In the next section we will add some files to that directory.

Try these, too.

The first ls above lists out the files of user jk. This is something you might do when copying files from your professor. In the output of the first ls command, you should see an inclass/ entry. The slash at the end of inclass indicates it is a directory.

The second ls above lists the files in the /home/jk/inclass directory (~jk is shorthand for /home/jk).

The last example above uses the -l (lower-case L) option, which shows the long format for listing files. This shows extra info on the files and directories, such as the owner (jk) and size of the file, and who has access to read and write the file.

In the next section we will copy the hello.py file into our testdir, so we can view and edit the file.

The cp command is used to copy a file. The format of the command is cp file newfile, and this makes a copy of file called newfile.

For example, to make a backup copy of a file named prog.py, you could run cp prog.py backup-prog.py

Try this! Let’s change into our testdir directory and then copy the hello.py file from user jk:

The above pwd output should show you are in your testdir directory. The ls should now show you have a copy of hello.py in your testdir directory.

Remember: if you’re ever lost, a simple cd command will put you back in your home directory (/home/username).

One more to try! Copy over the unix_commands file from our /scratch/usingunix directory:

Don’t forget the dot (.) at the end of that cp command! Using a dot for the newfile part of the copy command is a shortcut for "name the copy the same as the original file". When you run ls, you should now have a copy of the unix_commands file.

In the next section we will see how to view the contents of a file.

Sometimes we want to edit or change a file, and sometimes we just want to see the contents of the file.

To see the contents of the file there are two unix commands: less and cat.

The cat command (short for concatenate) can be used to just dump the contents of the file to the screen. If the file is large, the contents may scroll off the top of the terminal.

Try the cat command! If you are still in testdir, run the cat command on the two files we now have in there.

To view a file one page at a time, use the less command:

Hit q to quit out of less at any time.

There are a variety of text editors on our computers. This semester, CS21 students will use vscode. Some classes might also use vim or emacs.

Your class web page or instructor may suggest which editor is best for your class.

The mv command is used to move or rename a file. The format of the move command is similar to the copy command: mv file newfile. For example, to rename a file from badname.py to goodname.py: mv badname.py goodname.py

You can also move a file into a different directory with mv file directoryname

The rm command is used to remove a file. For example, to remove a file called oldprog.py: rm oldprog.py

Examples to try!

The above commands should copy a file, then rename it, show the contents of the file, and finally remove it. When you remove the file, it will ask "remove myprog.py?", to which you can answer either 'y' or 'n'.

When you are done for the day you can log out of the terminal window with Ctrl-d (hold down the Ctrl key and then hit the d key).

If you are in one of our labs, logged in at a computer console, please always remember to log out when you are done. Quit any terminals and browsers you have running, then log out of the window manager session. This keeps your files and account safe, and frees up resources for other students to use.