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~~DISCUSSION:off~~

The Bash Hackers Wiki

![](keywords>bash shell linux scripting)

<WRAP center round box 90%> This wiki is intended to hold documentation of any kind about GNU Bash. The main motivation was to provide human-readable documentation and information so users aren't forced to read every bit of the Bash manpage - which can be difficult to understand. However, the docs here are not meant as a newbie tutorial.

This wiki and any programs found in this wiki are free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This wiki and its programs are distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program. If not, see <http://www.gnu.org/licenses/>.

What would YOU like to see here? (outdated and locked, please use the discussions)

Stranger! Feel free to register and comment or edit the contents. There is a Bash Hackers Wiki needs love page that lists some things to do. The registration is only there to prevent SPAM. </WRAP>

Scripting and general information

Code snippets

There is a section that holds small code snippets.

See also some Bash source code excerpts.

How to....

Doing specific tasks: concepts, methods, ideas:

Bash syntax and operations

<WRAP column 40%> Compound commands

Compound commands overview
Grouping
{ ...; } command grouping
( ... ) command grouping in a subshell
Conditionals
[[ ... ]] conditional expression
if ...; then ...; fi conditional branching
case ... esac pattern-based branching
Loops
for word in ...; do ...; done classic for-loop
for ((x=1; x<=10; x++)); do ...; done C-style for-loop
while ...; do ...; done while loop
until ...; do ...; done until loop
Misc
(( ... )) arithmetic evaluation
select word in ...; do ...; done user selections

</WRAP>

<WRAP column 40%> Expansions and substitutions

Introduction to expansions and substitutions
{A,B,C} {A..C} Brace expansion
~/ ~root/ Tilde expansion
$FOO ${BAR%.mp3} Parameter expansion
`command` $(command) Command substitution
<(command) >(command) Process substitution
$((1 + 2 + 3)) $[4 + 5 + 6] Arithmetic expansion
Hello <---> Word! Word splitting
/data/*-av/*.mp? Pathname expansion

</WRAP> <WRAP clear></WRAP>

Builtin Commands

This is a selection of builtin commands and command-like keywords, loosely arranged by their common uses. These are provided directly by the shell, rather than invoked as standalone external commands.

<WRAP column 46%>

Declaration commands
<wrap center round lo todo box 80%>Commands that set and query attributes/types, and manipulate simple datastructures.</wrap>		 Alt Type
declare Display or set shell variables or functions along with attributes. typeset builtin
export Display or set shell variables, also giving them the export attribute. typeset -x special builtin
eval Evaluate arguments as shell code. - special builtin
local Declare variables as having function local scope. - builtin
readonly Mark variables or functions as read-only. typeset -r special builtin
unset Unset variables and functions. - special builtin
shift Shift positional parameters - special builtin
I/O
<wrap center round lo todo box 80%>Commands for reading/parsing input, or producing/formatting output of standard streams.</wrap>		 Alt Type
coproc Co-processes: Run a command in the background with pipes for reading / writing its standard streams. - keyword
echo Create output from arguments. - builtin
mapfile Read lines of input into an array. readarray builtin
printf "advanced echo." - builtin
read Read input into variables or arrays, or split strings into fields using delimiters. - builtin
Configuration and Debugging
<wrap center round lo todo box 80%>Commands that modify shell behavior, change special options, assist in debugging.</wrap>		 Alt Type
caller Identify/print execution frames. - builtin
set Set the positional parameters and/or set options that affect shell behaviour. - special builtin
shopt set/get some bash-specific shell options. - builtin

</WRAP>

<WRAP column 46%>

Control flow and data processing
<wrap center round lo todo box 80%>Commands that operate on data and/or affect control flow.</wrap>		 Alt Type
colon "true" null command. true special builtin
dot Source external files. source special builtin
false Fail at doing nothing. - builtin
continue / break continue with or break out of loops. - special builtin
let Arithmetic evaluation simple command. - builtin
return Return from a function with a specified exit status. - special builtin
[ The classic test simple command. test builtin
Process and Job control
<wrap center round lo todo box 80%>Commands related to jobs, signals, process groups, subshells.</wrap>		 Alt Type
exec Replace the current shell process or set redirections. - special builtin
exit Exit the shell. - special builtin
kill Send a signal to specified process(es) - builtin
trap Set signal handlers or output the current handlers. - special builtin
times Display process times. - special builtin
wait Wait for background jobs and asynchronous lists. - builtin
Alt Type

</WRAP> <WRAP clear></WRAP> <WRAP hide> previous alphabetical version <WRAP column 40%>

A-G
caller identify/print execution frames (Bash builtin)
coproc Co-processes (Bash keyword)
declare display or set shell variables or functions along with attributes (Bash builtin, synonym: typeset)
exec replace the shell, set redirections (Bash builtin)
I-N
let arithmetic evaluation - an old fashioned way (Bash builtin)
mapfile Mapping lines of input to an array, also named readarray (Bash builtin)

</WRAP>

<WRAP column 40%>

O-T
printf "advanced echo" (Bash builtin)
read getting input from stdin (Bash builtin)
readonly mark variables or functions as read-only (Bash builtin)
set control positional parameters and shell behaviour (Bash builtin)
shopt set/get shell options (Bash builtin)
test the classic test command (Bash builtin)
U-Z
unset unset variables and functions (Bash builtin)

</WRAP> <WRAP clear></WRAP> </WRAP>

Dictionary

💡 A list of expressions, words, and their meanings is here.

Links

Official Bash links

Recommended Shell resources

Documentation / Reference

Assorted interesting links

Bash Libraries (needs review)

<div hide>

Most wanted

Statistics for Month: April 2012
Rank Views Article
1 6833 getopts_tutorial (March: 11663)
2 4025 printf (March: 7079)
3 2861 quoting (March: 5730)
4 2854 classictest (March: 6145)
5 2222 pe (March: 4540)
6 1760 posparams (March: 3591)
7 1249 bash4 (March: --)
8 1212 edit-ed (March: 2727)
9 1205 read (March: --)
10 1182 mutex (March: --)
  • "Total visits": 35144
  • The overall "start" page is not counted

</div>

Contact

<WRAP column 40%> Visit us in irc.freenode.net, channel #bash ;-)

If you have critiques or suggestions, please feel free to send a mail using the contact form on the right. Note that there is a simple discussion option below every article.

Please also see the imprint if you have problems with the site and its contents (legality, ...)!

It also would be nice to drop a line when

  • it helped you
  • it didn't help you (something missing / unclear)
  • you like it
  • you don't like it
  • you found mistakes / bugs

Simply: Reader's feedback </WRAP>

<WRAP column 40%> ![](contact>subj=Wiki reader feedback) </WRAP>