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Shell Customization

CS155 Customization

Automatic scripts

• When your shell starts up, it reads commands, just as if you’d typed them, from a special file.
• Which file? It depends on which shell you’re using:
  • csh reads from ~/.cshrc
  • bash reads from ~/.bashrc
  • ksh reads from ~/.kshrc
  • zsh reads from ~/.zshrc
• Do you see a pattern?

What’s the syntax?

• What’s the syntax for one of these rc files?
• It depends on the shell.
• ~/.cshrc contains C-shell syntax, ~/.bashrc contains commands in the style of bash, etc.
• From now on, we will devote ourselves to bash.

Environment Variables

Customization usually means setting environment variables.

    export var="value"
    export TZ="America/Denver"

Remember, all examples from now on are bash only.

Inheritance

• Environment variables are inherited, so your children see the changes.
• By “children”, we mean sub-processes, or commands. date is often spawned by the shell, so it’s a “child” of the shell.
• If you were mutated by a gamma bomb, and became the Incredible Hulk, your future children would inherit your mutation, but your existing children and your parents would be unaffected.

Changing your PATH

To help the shell find programs directory /newbin, add it to the beginning of the environment variable PATH:

    export PATH="/newbin:$PATH"

Why did we use "double quotes" as opposed to 'single quotes'?

Changing your prompt

To change your interactive prompt, set the appropriate variable:

    PS1="$USER> "

Why didn’t we use export? That’s because this variable is private to the shell, and not for the user of other programs.

Creating new commands

To create a new command, use alias:

    alias hi="echo Howdy!"
    unalias hi
    alias h="history"
    alias mkx="chmod u+x"

umask

% rm -f x y
% umask ugo=rwx
% touch x
% umask u=rwx,g=r,o=
% touch y
% ls -l x y
-rw-rw-rw- 1 cs155 class 0 Feb 14 20:45 x
-rw-r----- 1 cs155 class 0 Feb 14 20:45 y

• umask sets the default permissions for new files.
• A umask of ugo=rwx is very trusting
• A umask of u=rwx,go= is paranoid.
• Put the appropriate umask in ~/.bashrc file.