Editing Bash (Unix shell) (section)

==== Shell and Session Startup Files (a.k.a., "Dot Files") ====
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When Bash starts, it executes the commands in a variety of [[Hidden file and hidden directory#Unix and Unix-like environments|dot files]].<ref>{{Cite web |title=I Almost Get a Linux Editor and Compiler     |url=http://www.drdobbs.com/i-almost-get-a-linux-editor-and-compiler/184404693     |url-status=live     |archive-url=https://web.archive.org/web/20210302212410/https://www.drdobbs.com/i-almost-get-a-linux-editor-and-compiler/184404693     |archive-date=March 2, 2021     |access-date=2020-09-12     |website=Dr. Dobb's   |quote=But virtually all the configure and install scripts that come with open-source programs are written for bash, and if you want to understand those scripts, you have to know bash.    }}</ref> Unlike Bash shell scripts, dot files do typically have neither the execute permission enabled nor an [[interpreter directive]] like <code>#!/bin/bash</code>.

===== Legacy-compatible Bash startup example =====
The example <code>~/.bash_profile</code> below is compatible with the Bourne shell and gives semantics similar to csh for the <code>~/.bashrc</code> and <code>~/.bash_login</code>. The <code>[ -r ''filename'' ] && cmd</code> is a [[short-circuit evaluation]] that tests if ''filename'' exists and is readable, skipping the part after the <code>&&</code> if it is not.

<syntaxhighlight lang="bash">
[ -r ~/.profile ] &&. ~/.profile             # set up environment, once, Bourne-sh syntax only
if [ -n "$PS1" ]; then                       # are we interactive?
   [ -r ~/.bashrc     ] &&. ~/.bashrc        # tty/prompt/function setup for interactive shells
   [ -r ~/.bash_login ] &&. ~/.bash_login    # any at-login tasks for login shell only
fi                                            # End of "if" block
</syntaxhighlight>

===== Operating system issues in Bash startup =====
Some versions of [[Unix]] and [[Linux]] contain Bash system startup scripts, generally under the <code>/etc</code> directory. Bash executes these files as part of its standard initialization, but other startup files can read them in a different order than the documented Bash startup sequence. The default content of the root user's files may also have issues, as well as the skeleton files the system provides to new user accounts upon setup. The startup scripts that launch the [[X window system]] may also do surprising things with the user's Bash startup scripts in an attempt to set up user-environment variables before launching the [[window manager]]. These issues can often be addressed using a <code>~/.xsession</code> or <code>~/.xprofile</code> file to read the <code>~/.profile</code> — which provides the environment variables that Bash shell windows spawned from the window manager need, such as [[xterm]] or [[Gnome Terminal]].