1. What is the difference between .bashrc and .bash_profile?

    Solutions

    The difference concerns the difference between a “login shell” and a “non-login shell”. A shell is a login shell the first time you log in (i.e., when you first ssh). You can create non-login shells by running the bash command from an existing shell.

    With that background, we can now appreciate the difference between the two files.

    • .bash_profile gets run when you start a *login shell
    • .bashrc gets run when you start a non-login shell

    For most people, you don’t care about the difference so a common procedure is to have all of your configuratin in your .bashrc and source ~/.bashrc from your .bash_profile.

  2. Say I have a python script (you can run a python script as a bash command by doing python script.py).

    • a) I want to be able to run it as a command from any directory, what do I need to do to accomplish this?
    • b) Now I want it to run every time I login to Attu, how would I do this??
    Solutions
    • a) alias randomnumber="python script.py" (note you would likely want to use an absolute path to make sure you can run it from any directory)
    • b) Add it to your .bash_profile

  3. How could I make it so if I type attu in a shell on my local machine it will ssh into attu?

    Solutions

    alias attu="ssh username@attu.cs.washington.edu"

  4. How could I print all the files in my current directory that belong to the cse391 group?

    Solutions

    The first solution works generally, but fails in some minor edge cases such as a file named cse391. The second solution works more generally:

    ls -l | grep "cse391"
find . -group cse391

  5. I have the file run.sh, it currently has unknown permissions. Say I want the owner to have read, write, and execute permissions, the group to have only execute permissions, and others to have only execute and read permissions.

    • a) How can I accomplish this using letter codes?
    • b) What is an equivalent command using octal syntax?
    Solutions
    • a) chmod u+rwx,g+x,g-rw,o+rx,o-w run.sh
    • b) chmod 715 run.sh