Bash

Bash will attempt to execute a set of startup files depending on how it was invoked. See the Bash Startup Files section of the GNU Bash manual for a complete description.

The behavior of Bash and programs run by it can be influenced by a number of environment variables. Environment variables are used to store useful values such as command search directories, or which browser to use. When a new shell or script is launched it inherits its parent's variables, thus starting with an internal set of shell variables.

These shell variables in Bash can be exported in order to become environment variables:

VARIABLE=content
export VARIABLE

or with a shortcut

export VARIABLE=content

Environment variables are conventionally placed in or /etc/profile so that other Bourne-compatible shells can use them.

See Environment variables for more general information.

Tab completion is the option to auto-complete typed commands by pressing (enabled by default).

It may require up to three tab-presses to show all possible completions for a command. To reduce the needed number of tab-presses, see Readline#Faster completion.

By default, Bash only tab-completes commands, filenames, and variables. The package extends this by adding more specialized tab completions for common commands and their options, which can be enabled by sourcing (which has been already sourced in Arch's ). With , normal completions (such as ) will behave differently; however, they can be re-enabled with (see and for more detail).

By default, Bash only tab-completes file names following a command. You can change it to complete command names using complete -c:

~/.bashrc

complete -c man which

or complete command names and file names with : See the Bash man page for more completion options.

You can bind the up and down arrow keys to search through Bash's history (see: Readline#History and Readline Init File Syntax):

or to affect all readline programs:

The variable can prevent certain commands from being logged to the history.

To stop logging of consecutive identical commands:

To remove all but the last identical command:

To avoid saving commands that start with a space:

To avoid saving consecutive identical commands, and commands that start with a space:

~/.bashrc

export HISTCONTROL=ignoreboth

To remove all but the last identical command, and commands that start with a space:

See for details.

To disable the bash history only temporarily:

$ set +o history

The commands entered now are not logged to the .

For example, now you can hash passwords with printf secret | sha256sum, or hide GPG usage like and your secret is not written to disk.

To enable history:

$ set -o history

To disable all bash history:

... and just to make sure, destroy your old histfile forever:

$ wipe -i -l2 -x4 -p4 "$HISTFILE"
$ ln -sv /dev/null "$HISTFILE"

Zsh can invoke the manual for the command preceding the cursor by pressing . A similar behaviour is obtained in Bash using this Readline bind:

This assumes are you using the (default) Emacs editing mode.

See Bash/Prompt customization.

is a command line editor written in pure Bash which replaces Readline. It has many enhanced features like syntax highlighting, autosuggestions, menu-completion, abbreviations, Vim editing mode, hook functions, and more.

After installing it, source it in an interactive session. Configurations are explained in depth in the ~/.blerc file and at the wiki. The stable package is also available.

pkgfile includes a "command not found" hook that will automatically search the official repositories, when entering an unrecognized command.

You need to source the hook to enable it, for example:

~/.bashrc

source /usr/share/doc/pkgfile/command-not-found.bash

Then attempting to run an unavailable command will show the following info:

You can disable the Ctrl+z feature (pauses/closes your application) by wrapping your command like this:

#!/bin/bash
trap "" 20
adom

Now, when you accidentally press Ctrl+z in instead of , nothing will happen because Ctrl+z will be ignored.

To clear the screen after logging out on a virtual terminal:

Bash can automatically prepend when entering just a path in the shell. For example:

But after adding one line into file:

~/.bashrc

...
shopt -s autocd
...

You get:

[user@host ~]$ /etc
cd /etc
[user@host etc]$

is a python script which allows navigating the file system by searching for strings in a database with the user's most-visited paths.

is an alternative which has additional features and performance improvements compared to the original  and can serve as a drop-in replacement for autojump.

For the current session, to disallow existing regular files to be overwritten by redirection of shell output:

$ set -o noclobber

This is identical to .

To make the changes persistent for your user:

To manually overwrite a file while noclobber is set:

$ echo "output" >| file.txt

and  can be used to push or pop directories to a stack while switching to them. This can be useful for "replaying" your navigation history.

[user@host ~] pushd /tmp/dir1
[user@host /tmp/dir1] pushd /var/lib
[user@host/var/lib] popd
[user@host/tmp/dir1] popd
[user@host ~]

See .

When resizing a terminal emulator, Bash may not receive the resize signal. This will cause typed text to not wrap correctly and overlap the prompt. The checkwinsize shell option checks the window size after each command and, if necessary, updates the values of and .

If you have set the option and you find that repeatedly hitting causes the shell to exit, it is because this option only allows 10 consecutive invocations of this keybinding (or 10 consecutive EOF characters, to be precise), before exiting the shell.

To allow higher values, you have to use the IGNOREEOF variable.

For example:

export IGNOREEOF=100

The package analyzes bash (and other shell) scripts, prints possible errors, and suggests better coding.

There is also the web site shellcheck.net of the same purpose, based on this program.

• Greg's Wiki
• GregsWiki:BashGuide
• GregsWiki:BashFAQ
• Bash Hackers Wiki
• Bash Hackers Wiki: List of Bash online tutorials
• Quote Tutorial

• An active and friendly IRC channel for Bash

• How to change the title of an xterm