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Revision as of 04:12, 16 April 2013
zh-CN:Bash Template:Article summary start Template:Article summary text Template:Article summary heading Template:Article summary wiki Template:Article summary wiki Template:Article summary wiki Template:Article summary end Bash (Bourne-again Shell) is a 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.
Contents
- 1 Invocation
- 2 Configuration
- 3 Command line
- 4 Aliases
- 5 Functions
- 6 Tips and tricks
- 6.1 Prompt customization
- 6.2 Tab completion
- 6.3 The "command not found" hook
- 6.4 Display error codes
- 6.5 Disable Ctrl+z in terminal
- 6.6 Clear the screen after logging out
- 6.7 ASCII art, fortunes and cowsay
- 6.8 ASCII Historical Calendar
- 6.9 Customise Title
- 6.10 Fix line wrap on window resize
- 6.11 History completion
- 6.12 Auto "cd" when entering just a path
- 7 See also
Invocation
Bash behaviour can be altered depending on how it is invoked. Some descriptions of different modes follow.
Login shell
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.
Interactive shell
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.
POSIX compliance
Bash can be run with enhanced POSIX compliance by starting Bash with the --posix
command-line option or executing ‘set -o posix
’ while Bash is running.
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
.
Configuration
The following files can be used to configure bash:
-
/etc/profile
-
~/.bash_profile
-
~/.bash_login
-
~/.profile
-
/etc/bash.bashrc
(Non-standard: only some distros, Arch included) -
~/.bashrc
-
~/.bash_logout
These files are commonly used:
-
/etc/profile
is sourced by all Bourne-compatible shells upon login. It sets up an environment upon login and loads application-specific (/etc/profile.d/*.sh
) settings. -
~/.profile
is read and sourced by bash when an interactive login shell is started. -
~/.bashrc
is read and sourced by bash when a non-login interactive shell is started, for example, when you open a virtual console from the desktop environment. This file is useful for setting up a user-specific shell environment.
Configuration file sourcing order at startup
These files are sourced by bash in different circumstances.
- if interactive + login shell →
/etc/profile
then the first readable of~/.bash_profile
,~/.bash_login
, and~/.profile
- Bash will source
~/.bash_logout
upon exit.
- Bash will source
- if interactive + non-login shell →
/etc/bash.bashrc
then~/.bashrc
- if login shell + legacy mode →
/etc/profile
then~/.profile
And by default in Arch:
-
/etc/profile
(indirectly) sources/etc/bash.bashrc
-
/etc/skel/.bash_profile
which users are encouraged to copy to~/.bash_profile
, sources~/.bashrc
which means that /etc/bash.bashrc
and ~/.bashrc
will be executed for all interactive shells, whether they are login shells or not.
Shell and environment variables
The behavior of bash and programs run by it can be influenced by a number of environment variable. 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[1].
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.
Aliases
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
.
An example excerpt from ~/.bashrc
covering several time-saving aliases:
~/.bashrc
# modified commands alias diff='colordiff' # requires colordiff package alias grep='grep --color=auto' alias more='less' alias df='df -h' alias du='du -c -h' alias mkdir='mkdir -p -v' alias nano='nano -w' alias ping='ping -c 5' alias ..='cd ..' # new commands alias da='date "+%A, %B %d, %Y [%T]"' alias du1='du --max-depth=1' alias hist='history | grep' # requires an argument alias openports='ss --all --numeric --processes --ipv4 --ipv6' alias pg='ps -Af | grep $1' # requires an argument (note: /usr/bin/pg is installed by the util-linux package; maybe a different alias name should be used) # privileged access if [ $UID -ne 0 ]; then alias sudo='sudo ' alias scat='sudo cat' alias svim='sudo vim' alias root='sudo su' alias reboot='sudo reboot' alias halt='sudo halt' alias update='sudo pacman -Su' alias netcfg='sudo netcfg2' fi # ls alias ls='ls -hF --color=auto' alias lr='ls -R' # recursive ls alias ll='ls -l' alias la='ll -A' alias lx='ll -BX' # sort by extension alias lz='ll -rS' # sort by size alias lt='ll -rt' # sort by date alias lm='la | more' # safety features alias cp='cp -i' alias mv='mv -i' alias rm='rm -I' # 'rm -i' prompts for every file alias ln='ln -i' alias chown='chown --preserve-root' alias chmod='chmod --preserve-root' alias chgrp='chgrp --preserve-root' # pacman aliases (if necessary, replace 'pacman' with your favorite AUR helper and adapt the commands accordingly) alias pac="sudo /usr/bin/pacman -S" # default action - install one or more packages alias pacu="/usr/bin/pacman -Syu" # '[u]pdate' - upgrade all packages to their newest version alias pacr="sudo /usr/bin/pacman -Rs" # '[r]emove' - uninstall one or more packages alias pacs="/usr/bin/pacman -Ss" # '[s]earch' - search for a package using one or more keywords alias paci="/usr/bin/pacman -Si" # '[i]nfo' - show information about a package alias paclo="/usr/bin/pacman -Qdt" # '[l]ist [o]rphans' - list all packages which are orphaned alias pacc="sudo /usr/bin/pacman -Scc" # '[c]lean cache' - delete all not currently installed package files alias paclf="/usr/bin/pacman -Ql" # '[l]ist [f]iles' - list all files installed by a given package alias pacexpl="/usr/bin/pacman -D --asexp" # 'mark as [expl]icit' - mark one or more packages as explicitly installed alias pacimpl="/usr/bin/pacman -D --asdep" # 'mark as [impl]icit' - mark one or more packages as non explicitly installed # '[r]emove [o]rphans' - recursively remove ALL orphaned packages alias pacro="/usr/bin/pacman -Qtdq > /dev/null && sudo /usr/bin/pacman -Rs \$(/usr/bin/pacman -Qtdq | sed -e ':a;N;$!ba;s/\n/ /g')"
Functions
Bash also supports functions. The following function will extract a wide range of compressed file types. Add the function to ~/.bashrc
and use it with the syntax extract <file1> <file2> ...
~/.bashrc
extract() { local c e i (($#)) || return for i; do c='' e=1 if [[ ! -r $i ]]; then echo "$0: file is unreadable: \`$i'" >&2 continue fi case $i in *.t@(gz|lz|xz|b@(2|z?(2))|a@(z|r?(.@(Z|bz?(2)|gz|lzma|xz))))) c='bsdtar xvf';; *.7z) c='7z x';; *.Z) c='uncompress';; *.bz2) c='bunzip2';; *.exe) c='cabextract';; *.gz) c='gunzip';; *.rar) c='unrar x';; *.xz) c='unxz';; *.zip) c='unzip';; *) echo "$0: unrecognized file extension: \`$i'" >&2 continue;; esac command $c "$i" e=$? done return $e }
shopt -s extglob
, by adding it to the ~/.bashrc
(see: http://mywiki.wooledge.org/glob#Options_which_change_globbing_behavior). It is enabled by default, if using Bash completion.Another way to do this is to install the unpAUR package from the AUR which contains a Perl script.
Very often changing to a directory is followed by the ls
command to list its contents. Therefore it is helpful to have a second function doing both at once.
In this example we will name it cl
and show an error message if the specified directory does not exist.
~/.bashrc
# cd and ls in one cl() { if [ -d "$1" ]; then cd "$1" ls else echo "bash: cl: '$1': Directory not found" fi }
Of course the ls command can be altered to fit your needs, for example $ ls -hall --color=auto
.
More Bash function examples can be found in BBS#30155.
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 PS1='\[\e[0;31m\]\u\[\e[m\] \[\e[1;34m\]\w\[\e[m\] \[\e[0;31m\]\$ \[\e[m\]\[\e[0;32m\] '
This $PS1
is useful for a root bash prompt, with red designation and green console text. For more info, see: Color Bash Prompt.
Tab completion
Tab completion allows for completing partially typed commands by pressing Template:Keypress twice.
Despite Bash's native support for basic file name, command, and variable tab completion the package bash-completion (available in the Official repositories) extends functionality by adding it to a wide range of commands and their options.
Start a new shell and it will be automatically enabled by /etc/bash.bashrc
.
$ ls file.*<tab><tab>
will not work unless you $ compopt -o bashdefault <prog>
for all programs you want to fallback to the normal glob expansions. See https://bbs.archlinux.org/viewtopic.php?id=128471 and https://www.gnu.org/software/bash/manual/html_node/Programmable-Completion-Builtins.htmlFaster completion
For a single press of Template:Keypress to produce a list of all possible completions (both when a partial or no completion is possible):
~/.inputrc
set show-all-if-ambiguous on
Alternatively, to produce such a list only when no completion is possible:
~/.inputrc
set show-all-if-ambiguous on set show-all-if-unmodified on
Manually
For basic completion use lines in the form of complete -cf your_command
:
~/.bashrc
complete -cf sudo complete -cf man
The "command not found" hook
The pkgfile package includes a "command not found" hook that will automatically search the official repositories when you enter an unrecognized command. Then it will display something like this:
An alternative "command not found" hook is also provided by the AUR package command-not-found, which will generate an output like the following:
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 ]
chiri ~/docs $ _Display error codes
To set trap
to intercept the non-zero return code of last program:
~/.bashrc
EC() { echo -e '\e[1;33m'code $?'\e[m\n'; } trap EC ERR
Disable Ctrl+z in terminal
You can disable the Template:Keypress feature (pauses/closes your application) by wrapping your command like this:
#!/bin/bash trap "" 20 adom
Now when you accidentally press Template:Keypress in adomAUR instead of Template:Keypress nothing will happen because Template:Keypress 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 art, fortunes and cowsay
Along with colors, system info and ASCII symbols, Bash can be made to display a piece of ASCII art on login. ASCII images can be found online and pasted into a text file, or generated from scratch. To set the image to display in a terminal on login, use:
~/.bashrc
cat /path/to/text/file
Random poignant, inspirational, silly or snide phrases can be found in fortune-mod.
$ fortune
It is Texas law that when two trains meet each other at a railroad crossing, each shall come to a full stop, and neither shall proceed until the other has gone.
fortune
displays quotes and phrases that are rather innoccuous. However, the package does contain a set of comments some people will find offensive, located in /usr/share/fortune/off/
. See the man page (man fortune
) for more info on these.To have a random phrase displayed when logging into a terminal, use:
~/.bashrc
command fortune
These two features can be combined, using the program cowsay:
command cowsay $(fortune)
The earth is like a tiny grain of sand, only much, much heavier. ----------------------------------------- \ ^__^ \ (oo)\_______ (__)\ )\/\ ||----w | || || (user@host)-(10:10 AM Wed Dec 22) --(~))--->
command cowthink $(fortune)
( The best cure for insomnia is to get a ) ( lot of sleep. -W.C. Fields ) ---------------------------------------- o ^__^ o (oo)\_______ (__)\ )\/\ ||----w | || || (user@host)-(10:10 AM Wed Dec 22) --(~))--->
The ASCII images are generated by .cow
text files located in /usr/share/cows
, and all themes can be listed with the cowsay -l
. These files can be edited to the user's liking; custom images can also be created from scratch or found on the net. The easiest way create a custom cow file is to use an existing one as a template. To test the custom file:
$ cowsay -f /path/to/file $(fortune)
This can produce some nice eye candy, and the commands used can be more complex. For a specialized example, take a look here. Another example, to use a random cow, random facial expression, and nicely wrap the text of long fortunes:
command fortune -a | fmt -80 -s | $(shuf -n 1 -e cowsay cowthink) -$(shuf -n 1 -e b d g p s t w y) -f $(shuf -n 1 -e $(cowsay -l | tail -n +2)) -n
________________________________________ ( Fry: I must be a robot. Why else would ) ( human women refuse to date me? ) ---------------------------------------- o o o ,'``.._ ,'``. :,--._:)\,:,._,.: :`--,''@@@:`...';\ `,'@@@@@@@`---'@@`. /@@@@@@@@@@@@@@@@@: /@@@@@@@@@@@@@@@@@@@\ ,'@@@@@@@@@@@@@@@@@@@@@:\.___,-. `...,---'``````-..._@@@@|:@@@@@@@\ ( )@@@;:@@@@)@@@\ _,-. `. (@@@//@@@@@@@@@@`'@@@@\ : `.//@@)@@@@@@)@@@@@,@; |`. _,'/@@@@@@@)@@@@)@,'@,' :`.`-..____..=:.-':@@@@@.@@@@@_,@@,' ,'\ ``--....-)=' `._,@@\ )@@@'``._ /@_@`. (@) /@@@@@) ; / \ \`-.' (@@@`-:`. `' ___..'@@_,-' |/ `.) `-. `.`.``-----``--,@@.' |/`.\`' ,','); ` (/ (/ (user@host)-(10:10 AM Wed Dec 22) --(~))--->
$ ponysay message
to say something and ponysay -l
for a complete list of ponies.
To create more ponies use util-say-gitAUR and store them in ~/.local/share/ponysay/ponies
and ~/.local/share/ponysay/ttyponies/
for desktop and TTY, respectivelyASCII 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 http://download.fedora.redhat.com/pub/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);
Customise 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\\";'
Fix line wrap on window resize
When you resize your xterm in vi for example, Bash will not get the resize signal, and the text you type will not wrap correctly, overlapping the prompt.
~/.bashrc
# check the window size after each command and, if necessary, # update the values of LINES and COLUMNS. shopt -s checkwinsize
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
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]
See also
- Advanced Bash Scripting Guide - Very good resource regarding shell scripting using bash
- Bash Reference Manual - Official reference (654K)
- Bash Hackers Wiki - Excellent Bash Wiki
- Bashscripts.org - Forum for bash coders.
- Bash Scripting by Example
- Completion Guide
- Greg's Wiki - Highly recommended
- man page
- Quote Tutorial
- irc://irc.freenode.net#bash - Active and friendly Internet Relay Chat channel for Bash.
- http://chakra-project.org/wiki/index.php/Startup_files
- The Bourne-Again Shell - The third chapter of The Architecture of Open Source Applications
- How to change the title of an xterm
- Readline Init File Syntax
- Custom Bash Commands & Functions