Bash (Русский)
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Bash (Bourne-again Shell) is a command-line shell/programming language by the GNU Project. Its name is a homaging reference to its predecessor: the long-deprecated Bourne shell. Bash can be run on most UNIX-like operating systems, including GNU/Linux.
Invocation
Bash behaviour can be altered depending on how it is invoked. Some descriptions of different modes follow.
If Bash is spawned by login
in a tty, by an SSH daemon, or similar means, it is considered a login shell. This mode can also be engaged using the -l
or --login
command line options.
Bash is considered an interactive shell if it is started neither with the -c
option nor any non-option arguments, and whose standard input and error are connected to terminals.
Legacy mode
In Arch /bin/sh
(which used to be the Bourne shell executable) is symlinked to /bin/bash
. If Bash is invoked with the name sh
, it tries to mimic the startup behavior of historical versions of sh
, including POSIX compability.
A login shell run in legacy mode sources /etc/profile
, then ~/.profile
.
Configuration files
File | When file commands are read and executed (sourced) |
---|---|
/etc/profile
|
An interactive shell that is also a login shell (for example, from /usr/bin/login ). Sources application settings in /etc/profile.d/*.sh , and /etc/bash.bashrc .
|
/etc/bash.bashrc
|
An interactive shell (for example, a terminal emulator). Depends on the -DSYS_BASHRC="/etc/bash.bashrc" compilation flag. Sources /usr/share/bash-completion/bash_completion .
|
~/.bash_profile
|
An interactive shell that is also a login shell. Per-user, after /etc/profile . If this file does not exist, ~/.bash_login and ~/.profile are checked in that order. The skeleton file /etc/skel/.bash_profile also sources ~/.bashrc .
|
~/.bashrc
|
An interactive shell. Per-user, after /etc/bash.bashrc .
|
~/.bash_logout
|
After exit of a login shell. |
In short, all interactive shells source /etc/bash.bashrc
and ~/.bashrc
, while interactive login shells also source /etc/profile
and ~/.bash_profile
.
See the INVOCATION section of man 1 bash
or [2] for the complete sequence.
Shell and environment variables
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[3].
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 ~/.profile
or /etc/profile
so that all bourne-compatible shells can use them.
See Environment variables for more general information.
Command line
Bash command line is managed by the separate library called Readline. Readline provides a lot of shortcuts for interacting with the command line i.e. moving back and forth on the word basis, deleting words etc. It is also Readline's responsibility to manage history of input commands. Last, but not least, it allows you to create macros.
Tab completion
Tab completion is the option to auto-complete partial typed commands by pressing Tab
twice (enabled by default).
Single-tab ability
For single press Tab
results for when a partial or no completion is possible:
~/.inputrc
set show-all-if-ambiguous on
Alternatively, for results when no completion is possible:
~/.inputrc
set show-all-if-unmodified on
Additional programs and options
Bash has native support for for tab completion of: commands, filenames, and variables. This functionality can be extended with the package bash-completion; it extends its functionality by adding a subset of tab completions to popular commands and their options. With bash-completion know that normal completions (such as $ ls file.*<tab><tab>
) will behave different; however, they can be re-enabled with $ compopt -o bashdefault <prog>
(see [4] and [5] for more detail). Also for older systems bash-completion may not be resourcefully convenient.
Additional programs and options manually
For basic completion use lines in the form of complete -cf your_command
(these will conflict with the bash-completion settings):
~/.bashrc
complete -cf sudo complete -cf man
History completion
History completion bound to arrow keys (down, up) (see: Readline#History and Readline Init File Syntax):
~/.bashrc
bind '"\e[A": history-search-backward' bind '"\e[B": history-search-forward'
or:
~/.inputrc
"\e[A": history-search-backward "\e[B": history-search-forward
Fast word movement with Ctrl
Bash allows to quickly move between words with Ctrl+Left
and Ctrl+Right
.
~/.inputrc
"\e[1;5C": forward-word "\e[1;5D": backward-word "\e[5C": forward-word "\e[5D": backward-word "\e\e[C": forward-word "\e\e[D": backward-word
Mimic Zsh run-help ability
Zsh can invoke the manual for the written command pushing Alt+h
.
A similar behaviour is obtained in Bash by appending this line in your inputrc
file:
/etc/inputrc
"\eh": "\C-a\eb\ed\C-y\e#man \C-y\C-m\C-p\C-p\C-a\C-d\C-e"
Псевдонимы
alias is a command, which enables a replacement of a word with another string. It is often used for abbreviating a system command, or for adding default arguments to a regularly used command.
Personal aliases are preferably stored in ~/.bashrc
, and system-wide aliases (which affect all users) belong in /etc/bash.bashrc
. See [6] and Pacman tips#Shortcuts for example aliases.
For functions, see Bash/Functions.
Tips and tricks
Prompt customization
The Bash prompt is governed by the variable $PS1
. To colorize the Bash prompt, use:
~/.bashrc
#PS1='[\u@\h \W]\$ ' # To leave the default one #DO NOT USE RAW ESCAPES, USE TPUT reset=$(tput sgr0) red=$(tput setaf 1) blue=$(tput setaf 4) green=$(tput setaf 2) PS1='\[$red\]\u\[$reset\] \[$blue\]\w\[$reset\] \[$red\]\$ \[$reset\]\[$green\] '
This $PS1
is useful for a root Bash prompt, with red designation and green console text. For more info, see: Color Bash Prompt.
Customize title
The $PROMPT_COMMAND
variable allows you to execute a command before the prompt. For example, this will change the title to your full current working directory:
~/.bashrc
export PROMPT_COMMAND='echo -ne "\033]0;$PWD\007"'
This will change your title to the last command run, and make sure your history file is always up-to-date:
~/.bashrc
export HISTCONTROL=ignoreboth export HISTIGNORE='history*' export PROMPT_COMMAND='history -a;echo -en "\e]2;";history 1|sed "s/^[ \t]*[0-9]\{1,\} //g";echo -en "\e\\";'
Command-not-found (AUR)
pkgfile includes a "command not found" hook that will automatically search the official repositories, when entering an unrecognized command. An alternative "command not found" hook is provided by the AUR package command-not-foundAUR. Usage example:
$ abiword
The command 'abiword' is been provided by the following packages: abiword (2.8.6-7) from extra [ abiword ] abiword (2.8.6-7) from staging [ abiword ] abiword (2.8.6-7) from testing [ abiword ]
To load it automatically:
~/.bashrc or ~/.zshrc
[ -r /etc/profile.d/cnf.sh ] && . /etc/profile.d/cnf.sh
Disable Ctrl+z in terminal
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 adomAUR instead of Shift+z
nothing will happen because Ctrl+z
will be ignored.
Clear the screen after logging out
To clear the screen after logging out on a virtual terminal:
~/.bash_logout
clear reset
ASCII historical calendar
To install calendar files in your ~/.calendar
directory you will need the rpmextract package installed. Then from your home directory, run the following:
$ mkdir -p ~/.calendar $ curl -o calendar.rpm ftp://ftp.univie.ac.at/systems/linux/fedora/epel/5/x86_64/calendar-1.25-4.el5.x86_64.rpm $ rpm2cpio calendar.rpm | bsdtar -C ~/.calendar --strip-components=4 -xf - ./usr/share/c*
This will then print out the calendar items:
$ sed -n "/$(date +%m\\/%d\\\|%b\*\ %d)/p" $(find ~/.calendar /usr/share/calendar -maxdepth 1 -type f -name 'c*' 2>/dev/null);
Auto "cd" when entering just a path
Bash can automatically prepend cd
when entering just a path in the shell. For example:
$ /etc
bash: /etc: Is a directory
But after:
~/.bashrc
shopt -s autocd
You get:
[user@host ~] $ /etc cd /etc [user@host etc]
Troubleshooting
Line wrap on window resize
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 LINES
and COLUMNS
.
~/.bashrc
shopt -s checkwinsize
See also
- Bash Reference
- Bash manual page
- Readline Init File Syntax
- The Bourne-Again Shell - The third chapter of The Architecture of Open Source Applications
- Shellcheck - Check bash scripts for common errors
Tutorials
- BashGuide on Greg's Wiki
- BashFAQ on Greg's Wiki
- Bash Hackers Wiki
- Advanced Bash Scripting Guide
- Bash Scripting by Example
- Quote Tutorial
- Introduction to Bash