The Bash Hackers Wiki
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 (outdated and locked, please use the discussions)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.
Scripting and general information
- Bash v4 - a rough overview (unmaintained, since Bash 4 is more or less standard)
- Scripting with style – an assorted collection of style and optic hints
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:
- Small getopts tutorial (under construction!)
- Dissect a bad oneliner An example of a bad oneliner, breakdown and fix (by
kojoro) - Write tests for ./your-script.sh by using bashtest util
Bash syntax and operations
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 |
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 |
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.
| Declaration commands Commands that set and query attributes/types, and manipulate simple datastructures. | 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 Commands for reading/parsing input, or producing/formatting output of standard streams. | 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 Commands that modify shell behavior, change special options, assist in debugging. | 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 |
| Control flow and data processing Commands that operate on data and/or affect control flow. | 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 Commands related to jobs, signals, process groups, subshells. | 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 | ||
previous alphabetical version
| 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) |
| 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) |
Dictionary
Links
Official Bash links
- Chet Ramey's Bash page and its FAQ.
- Official Bash mailing lists:
- Bug reports: bug-bash@gnu.org (archives)
- General questions: help-bash@gnu.org (archives)
- Official Bash git repository:
- Browse: cgit
- Clone: git: ssh://git.sv.gnu.org/srv/git/bash.git • ssh: ssh://git.sv.gnu.org/srv/git/bash.git • http: http://git.savannah.gnu.org/r/bash.git
Recommended Shell resources
- Greg's wiki - Greg Wooledge's (aka "greycat") wiki – with MASSIVE information about Bash and UNIX® in general.
- Sven Mascheck's pages - A goldmine of information. A must-read.
- #ksh channel page - #ksh Freenode channel page maintains a solid collection of recommended links.
- The Grymoire Unix pages - Good scripting information, especially read the quoting guide.
- Heiner's "Shell Dorado" - Tips, tricks, links - for every situation.
- Advanced Bash-Scripting Guide - last update: 10 Mar 2014, but still very useful guide.
Documentation / Reference
- mksh (pdksh successor)
Assorted interesting links
- History and development of the traditional Bourne shell family - very interesting and nice to read!
- Linux in general, with some shell related stuff: nixCraft: Linux Tips, Hacks, Tutorials and Ideas
- Linux tutorials, guides and how-tos: RoseHosting Blog, bash script for installing WordPress and some basic shell commands
Bash Libraries (needs review)
- An oo-style bash library for bash 4 - provides tools for rapid script development and huge libraries.
- General purpose shell framework for bash 4 - in development.
- General purpose bash library for bash 4 - active development
Most wanted
| Statistics for Month: April 2012 | ||
|---|---|---|
| Rank | Views | Article |
| 1 | 6833 | Small getopts tutorial (March: 11663) |
| 2 | 4025 | The printf command (March: 7079) |
| 3 | 2861 | Quotes and escaping (March: 5730) |
| 4 | 2854 | The classic test command (March: 6145) |
| 5 | 2222 | Parameter expansion (March: 4540) |
| 6 | 1760 | Handling positional parameters (March: 3591) |
| 7 | 1249 | Bash 4 - a rough overview (March: –) |
| 8 | 1212 | Editing files via scripts with ed (March: 2727) |
| 9 | 1205 | The read builtin command (March: –) |
| 10 | 1182 | Lock your script (against parallel execution) (March: –) |
- "Total visits": 35144
- The overall "start" page is not counted
Contact
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
