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---
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hide: [navigation]
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tags:
- bash
- shell
- linux
- scripting
---
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# The Bash Hackers Wiki
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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.
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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.
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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.
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You should have received a copy of the GNU General Public License along with this program.
If not, see [http://www.gnu.org/licenses/ ](http://www.gnu.org/licenses/ ).
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[What would YOU like to see here? ](wishes ) (outdated and locked, please use the discussions)
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**Stranger!** Feel free to comment or edit the contents on GitHub.
There is a [Bash Hackers Wiki needs love page ](/meta/need_love ) that lists some things to do.
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## Scripting and general information
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- [Bash v4 - a rough overview ](bash4 ) (unmaintained, since Bash 4 is more or less standard)
- [style ](/scripting/style ) –
- [basics ](/scripting/basics )
- [newbie_traps ](/scripting/newbie_traps )
- [bashbehaviour ](/scripting/bashbehaviour )
- [posparams ](/scripting/posparams )
- [processtree ](/scripting/processtree )
- [obsolete ](/scripting/obsolete )
- [nonportable ](/scripting/nonportable )
- [debuggingtips ](/scripting/debuggingtips )
- [terminalcodes ](/scripting/terminalcodes )
- [tutoriallist ](/scripting/tutoriallist )
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## Code snippets
There is a [section that holds small code snippets ](/snipplets/start ).
See also [some Bash source code excerpts ](/misc/readthesourceluke ).
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## How to
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[Doing specific tasks: concepts, methods, ideas ](/howto/start ):
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- [Simple locking (against parallel run) ](/howto/mutex )
- [Rudimentary config files for your scripts ](/howto/conffile )
- [Editing files with ed ](/howto/edit-ed )
- [Collapsing Functions ](/howto/collapsing_functions )
- [Illustrated Redirection Tutorial ](/howto/redirection_tutorial )
- [Calculate with dc ](/howto/calculate-dc )
- [Introduction to pax - the POSIX archiver ](/howto/pax )
- [getopts_tutorial ](/howto/getopts_tutorial ) (*under construction!*)
- [dissectabadoneliner ](/howto/dissectabadoneliner ) An example of a bad oneliner, breakdown and fix (by `kojoro` )
- [Write tests for ./your-script.sh ](/howto/testing-your-scripts ) by using bashtest util
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## Bash syntax and operations
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- [Bash features overview by version ](/scripting/bashchanges )
- [Basic grammar rules ](/syntax/basicgrammar )
- [Quoting and character escaping ](/syntax/quoting )
- [Parsing and execution ](/syntax/grammar/parser_exec )
- [Some words about words... ](/syntax/words )
- [Patterns and pattern matching ](/syntax/pattern )
- [Arithmetic expressions ](/syntax/arith_expr )
- [List of shell options ](/internals/shell_options )
- [Redirection ](/syntax/redirection )
- [Special parameters and shell variables ](/syntax/shellvars )
- [Arrays ](/syntax/arrays )
## Compound commands
| [Compound commands overview ](/syntax/ccmd/intro ) | |
| ------------------------------------------------ | ---------------------------------------------------------------- |
| **Grouping** | |
| `{ ...; }` | [command grouping ](/syntax/ccmd/grouping_plain ) |
| `( ... )` | [command grouping in a subshell ](/syntax/ccmd/grouping_subshell ) |
| **Conditionals** | |
| `[[ ... ]]` | [conditional expression ](/syntax/ccmd/conditional_expression ) |
| `if ...; then ...; fi` | [conditional branching ](/syntax/ccmd/if_clause ) |
| `case ... esac` | [pattern-based branching ](/syntax/ccmd/case ) |
| **Loops** | |
| `for word in ...; do ...; done` | [classic for-loop ](/syntax/ccmd/classic_for ) |
| `for ((x=1; x<=10; x++)); do ...; done` | [C-style for-loop ](/syntax/ccmd/c_for ) |
| `while ...; do ...; done` | [while loop ](/syntax/ccmd/while_loop ) |
| `until ...; do ...; done` | [until loop ](/syntax/ccmd/until_loop ) |
| **Misc** | |
| `(( ... ))` | [arithmetic evaluation ](/syntax/ccmd/arithmetic_eval ) |
| `select word in ...; do ...; done` | [user selections ](/syntax/ccmd/user_select ) |
## Expansions and substitutions
| [Introduction to expansions and substitutions ](/syntax/expansion/intro ) | |
| ------------------------------------------------------------------------| ---------------------------------------------------- |
| `{A,B,C} {A..C}` | [Brace expansion ](/syntax/expansion/brace ) |
| `~/ ~root/` | [Tilde expansion ](/syntax/expansion/tilde ) |
| `$FOO ${BAR%.mp3}` | [Parameter expansion ](/syntax/pe ) |
| `` `command` $(command) `` | [Command substitution ](/syntax/expansion/cmdsubst ) |
| `<(command) >(command)` | [Process substitution ](/syntax/expansion/proc_subst ) |
| `$((1 + 2 + 3)) $[4 + 5 + 6]` | [Arithmetic expansion ](/syntax/expansion/arith ) |
| `Hello <---> Word!` | [Word splitting ](/syntax/expansion/wordsplit ) |
| `/data/*-av/*.mp?` | [Pathname expansion ](/syntax/expansion/globs ) |
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## Builtin Commands
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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
!!! note
Commands that set and query attributes/types, and manipulate simple datastructures.
| Command | Description | Alt | Type |
| -------------------------------------- | ---------------------------------------------------------------------- | ------------ | --------------- |
| [declare ](/commands/builtin/declare ) | Display or set shell variables or functions along with attributes. | `typeset` | builtin |
| [export ](/commands/builtin/export ) | Display or set shell variables, also giving them the export attribute. | `typeset -x` | special builtin |
| [eval ](/commands/builtin/eval ) | Evaluate arguments as shell code. | | special builtin |
| [local ](/commands/builtin/local ) | Declare variables as having function local scope. | | builtin |
| [readonly ](/commands/builtin/readonly ) | Mark variables or functions as read-only. | `typeset -r` | special builtin |
| [unset ](/commands/builtin/unset ) | Unset variables and functions. | | special builtin |
| [shift ](/commands/builtin/shift ) | Shift positional parameters | | special builtin |
### IO
!!! note
Commands for reading/parsing input, or producing/formatting output of standard streams.
| Command | Description | Alt | Type |
| ------------------------------------ | ---------------------------------------------------------------------- | ----------- | ---------|
| [coproc ](/syntax/keywords/coproc ) | Co-processes: Run a command in the background with pipes for reading / writing its standard streams. | | keyword |
| [echo ](/commands/builtin/echo ) | Create output from arguments. | | builtin |
| [mapfile ](/commands/builtin/mapfile ) | Read lines of input into an array. | `readarray` | builtin |
| [printf ](/commands/builtin/printf ) | "advanced `echo` " | | builtin |
| [read ](/commands/builtin/read ) | Read input into variables or arrays, or split strings into fields using delimiters. | | builtin |
### Configuration and Debugging
!!! note
Commands that modify shell behavior, change special options, assist in debugging.
| Command | Description | Alt | Type |
| ---------------------------------- | ----------------------------------------------------------------------------- | --- | --------------- |
| [caller ](/commands/builtin/caller ) | Identify/print execution frames. | | builtin |
| [set ](/commands/builtin/set ) | Set the positional parameters and/or set options that affect shell behaviour. | | special builtin |
| [shopt ](/commands/builtin/shopt ) | set/get some bash-specific shell options. | | builtin |
### Control flow and data processing
!!! note
Commands that operate on data and/or affect control flow.
| Command | Description | Alt | Type |
| --------------------------------------------------- | ---------------------------------------------------- | -------- | --------------- |
| [colon ](/commands/builtin/true ) | "true" null command. | `true` | special builtin |
| [dot ](/commands/builtin/source ) | Source external files. | `source` | special builtin |
| [false ](/commands/builtin/false ) | Fail at doing nothing. | | builtin |
| [continue / break ](/commands/builtin/continueBreak ) | continue with or break out of loops. | | special builtin |
| [let ](/commands/builtin/let ) | Arithmetic evaluation simple command. | | builtin |
| [return ](/commands/builtin/return ) | Return from a function with a specified exit status. | | special builtin |
| [[]](/commands/classictest) | The classic `test` simple command. | `test` | builtin |
### Process and Job control
!!! note
Commands related to jobs, signals, process groups, subshells.
| Command | Description | Alt | Type |
| -------------------------------- | ------------------------------------------------------ | --- | --------------- |
| [exec ](/commands/builtin/exec ) | Replace the current shell process or set redirections. | | special builtin |
| [exit ](/commands/builtin/exit ) | Exit the shell. | | special builtin |
| [trap ](/commands/builtin/trap ) | Set signal handlers or output the current handlers. | | special builtin |
| [kill ](/commands/builtin/kill ) | Send a signal to specified process(es) | | builtin |
| [times ](/commands/builtin/times ) | Display process times. | | special builtin |
| [wait ](/commands/builtin/wait ) | Wait for background jobs and asynchronous lists. | | builtin |
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## Dictionary
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A list of expressions, words, and their meanings is [here ](/dict/index ).
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## Links
### Official Bash links
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- [Chet Ramey's Bash page ](http://tiswww.case.edu/php/chet/bash/bashtop.html ) and its [FAQ ](http://tiswww.case.edu/php/chet/bash/FAQ ).
- [GNU Bash software page ](http://www.gnu.org/software/bash/ )
- Official Bash mailing lists:
- **Bug reports**: < bug-bash @ gnu . org > ([archives](http://mail.gnu.org/pipermail/bug-bash))
- **General questions**: < help-bash @ gnu . org > ([archives](http://mail.gnu.org/pipermail/help-bash))
- Official Bash git repository:
- **Browse**: [cgit ](http://git.savannah.gnu.org/cgit/bash.git )
- **Clone**: `git clone git.sv.gnu.org/srv/git/bash.git`
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### Recommended Shell resources
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- [Greg's wiki ](http://mywiki.wooledge.org/ ) - Greg Wooledge's (aka "greycat") wiki -- with **MASSIVE** information about Bash and UNIX(r) in general.
- [BashFAQ ](http://mywiki.wooledge.org/BashFAQ ) • [BashGuide ](http://mywiki.wooledge.org/BashGuide ) • [BashPitfalls ](http://mywiki.wooledge.org/BashPitfalls ) • [BashSheet ](http://mywiki.wooledge.org/BashSheet )
- [Sven Mascheck's pages ](http://www.in-ulm.de/~mascheck/ ) - A goldmine of information. A must-read.
- [#ksh channel page ](https://www.mirbsd.org/ksh-chan.htm ) - #ksh Freenode channel page maintains a solid collection of recommended links.
- [The Grymoire Unix pages ](http://www.grymoire.com/Unix/ ) - Good scripting information, especially read the [quoting ](http://www.grymoire.com/Unix/Quote.html ) guide.
- [Heiner's "Shell Dorado" ](http://www.shelldorado.com ) - Tips, tricks, links - for every situation.
- [The Single Unix Specification (version 4, aka POSIX-2008) ](http://pubs.opengroup.org/onlinepubs/9699919799/ )
- [The Austin Group ](http://www.opengroup.org/austin/ ) - [List archives ](http://dir.gmane.org/gmane.comp.standards.posix.austin.general ), [Bug tracker ](http://austingroupbugs.net/main_page.php )
- [comp.unix.shell FAQ ](http://cfajohnson.com/shell/cus-faq.html )
- [Advanced Bash-Scripting Guide ](https://tldp.org/LDP/abs/html/index.html ) - last update: 10 Mar 2014, but still very useful guide.
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#### Documentation / Reference
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- **Bash**: [man page ](http://tiswww.case.edu/php/chet/bash/bash.html ), [info page ](http://tiswww.case.edu/php/chet/bash/bashref.html )
- **AT& T ksh**: [ksh88 ](http://www2.research.att.com/sw/download/man/man1/ksh88.html ), [ksh93 ](http://www2.research.att.com/sw/download/man/man1/ksh.html )
- [mksh ](https://www.mirbsd.org/htman/i386/man1/mksh.htm ) (pdksh successor)
- [zsh ](http://zsh.sourceforge.net/Doc/ )
- [dash ](http://man7.org/linux/man-pages/man1/dash.1.html )
- [Heirloom Bourne shell ](http://heirloom.sourceforge.net/man/sh.1.html )
- [Thompson shell ](http://v6shell.org/man/osh.1.html )
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### Assorted interesting links
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- [History and development of the traditional Bourne shell family ](http://www.in-ulm.de/~mascheck/bourne/ ) - very interesting and nice to read!
- [Interview with Chet Ramey ](http://www.computerworld.com.au/article/222764/-z_programming_languages_bash_bourne-again_shell )
- [Interview with Steve Bourne ](http://www.computerworld.com.au/article/279011/a-z_programming_languages_sh ) • [Stephen Bourne - BSDCan 2015 keynote ](https://www.youtube.com/watch?v=2kEJoWfobpA )
- [Interview with David Korn ](http://news.slashdot.org/story/01/02/06/2030205/david-korn-tells-all )
- [Kernighan on the Unix pipeline (computerphile video) ](https://www.youtube.com/watch?v=bKzonnwoR2I )
- Linux in general, with some shell related stuff: [nixCraft: Linux Tips, Hacks, Tutorials and Ideas ](http://www.cyberciti.biz/ )
- Linux tutorials, guides and how-tos: [RoseHosting Blog ](https://www.rosehosting.com/blog/ ), [bash script for installing WordPress ](https://www.rosehosting.com/blog/script-install-wordpress-on-a-debianubuntu-vps/ ) and some [basic shell commands ](https://www.rosehosting.com/blog/basic-shell-commands-after-putty-ssh-logon/ )
- [Bashphorism list from the Bash IRC channel on Freenode ](/misc/bashphorisms )
- [Some more or less funny commandline stuff ](/misc/shell_humor )
- [How to Enable SSH on Ubuntu Tutorial ](https://thishosting.rocks/how-to-enable-ssh-on-ubuntu/ )
- [How To Make an Awesome Custom Shell with ZSH ](https://linuxstans.com/how-to-make-an-awesome-custom-shell-with-zsh/ )
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### Bash Libraries (needs review)
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- [An oo-style bash library for bash 4 ](http://sourceforge.net/projects/oobash/ ) - provides tools for rapid script development and huge libraries.
- [General purpose shell framework for bash 4 ](https://github.com/hornos/shf3 ) - in development.
- [General purpose bash library for bash 4 ](https://github.com/chilicuil/learn/blob/master/sh/lib ) - active development
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## Contact
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Visit us in [ircs://irc.libera.chat:6697 ](ircs://irc.libera.chat:6697 ), channel `#bash` ;-)
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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.
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Please also see the [imprint ](/user/thebonsai/imprint ) if you have problems with the site and its contents (legality, ...)!
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It also would be nice to drop a line when
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- it helped you
- it didn't help you (something missing / unclear)
- you like it
- you don't like it
- you found mistakes / bugs
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Simply: Reader's feedback.
