Unix shell initialization

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Page Contents

• Unix shell initialization
  • Shell modes
  • Shell init files
    • bash
    • zsh
    • dash
    • fish
  • Practical guide to which files get sourced when
  • Misc. things that affect $PATH
  • Final notes

Shell initialization files are ways to persist common shell configurations:

• $PATH and other environment variables
• shell prompt
• shell tab-completion
• aliases, functions
• key bindings

Shell modes

Which initialization files get sourced by the shell is dependent on the combination of modes in which a particular shell process runs. There are two main, non-exclusive modes:

• login - e.g. when user logs in to a system with non-graphical interface or via SSH;
• interactive - shell that has a prompt and whose standard input and error are both connected to terminals.

These modes can be manually activated with the following flags to bash/zsh:

• -l, --login
• -i

Here are some common operations and shell modes they result in:

• log in to a remote system via SSH: login + interactive
• execute a script remotely, e.g. ssh user@host 'echo $PWD' or with Capistrano: non‑login, non‑interactive
• execute a script remotely and request a terminal, e.g. ssh user@host -t 'echo $PWD': non-login, interactive
• start a new shell process, e.g. bash: non‑login, interactive
• run a script, bash myscript.sh: non‑login, non‑interactive
• run an executable with #!/usr/bin/env bash shebang: non‑login, non‑interactive
• open a new graphical terminal window/tab:
  • on Mac OS X: login, interactive
  • on Linux: non‑login, interactive

Shell init files

In order of activation:

bash

1. login mode:
   1. /etc/profile
   2. ~/.bash_profile, ~/.bash_login, ~/.profile (only first one that exists)
2. interactive non-login:
   1. /etc/bash.bashrc (some Linux; not on Mac OS X)
   2. ~/.bashrc
3. non-interactive:
   1. source file in $BASH_ENV

zsh

1. /etc/zshenv
2. ~/.zshenv
3. login mode:
   1. /etc/zprofile
   2. ~/.zprofile
4. interactive:
   1. /etc/zshrc
   2. ~/.zshrc
5. login mode:
   1. /etc/zlogin
   2. ~/.zlogin

dash

1. login mode:
   1. /etc/profile
   2. ~/.profile
2. interactive:
   1. source file in $ENV

fish

1. <install-prefix>/config.fish
2. /etc/fish/config.fish
3. ~/.config/fish/config.fish

Practical guide to which files get sourced when

• Opening a new Terminal window/tab:
  • bash
    • OS X: .bash_profile or .profile (1st found)
    • Linux: .profile (Ubuntu, once per desktop login session) + .bashrc
  • Zsh
    • OS X: .zshenv + .zprofile + .zshrc
    • Linux: .profile (Ubuntu, once per desktop login session) + .zshenv + .zshrc
• Logging into a system via SSH:
  • bash: .bash_profile or .profile (1st found)
  • Zsh: .zshenv + .zprofile + .zshrc
• Executing a command remotely with ssh or Capistrano:
  • bash: source file in $BASH_ENV
  • Zsh: .zshenv
• Remote git hook triggered by push over SSH:
  • no init files get sourced, since hooks are running within a restricted shell
  • PATH will be roughly: /usr/libexec/git-core:/usr/bin:/usr/bin:/bin:/usr/sbin:/sbin

Misc. things that affect $PATH

• OS X:
  • /etc/paths, /etc/paths.d/*
  • ~/.MacOSX/environment.plist - affects all graphical programs
  • /etc/launchd.conf
  • TextMate: Preferences -> Advanced -> Shell Variables
• Linux:
  • /etc/environment

Final notes

This guide was tested with:

• bash 4.2.37, 4.2.39
• Zsh 4.3.11, 5.0

On these operating systems/apps:

• Mac OS X 10.8 (Mountain Lion): Terminal.app, iTerm2
• Ubuntu 12.10: Terminal

See also:

• Environment Variables
• path_helper(8)
• launchd.conf(5)
• pam_env(8)