---
hide: [navigation]
tags:
  - bash
  - shell
  - linux
  - scripting
---

# 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/](http://www.gnu.org/licenses/).

[What would YOU like to see here?](wishes) (outdated and locked, please use the discussions)

**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.

## Scripting and general information

- [Bash v4 - a rough overview](bash4) (unmaintained, since Bash 4 is more or less standard)
- [style](/scripting/style) – an assorted collection of style and optic hints
- [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)

## Code snippets

There is a [section that holds small code snippets](/snipplets/start).

See also [some Bash source code excerpts](/misc/readthesourceluke).

## How to

[Doing specific tasks: concepts, methods, ideas](/howto/start):

- [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

## Bash syntax and operations

- [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)        |

## 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

!!! 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         |

## Dictionary

A list of expressions, words, and their meanings is [here](/dict/index).

## Links

### Official Bash links

- [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`

### Recommended Shell resources

- [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.

#### Documentation / Reference

- **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)

### Assorted interesting links

- [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/)

### Bash Libraries (needs review)

- [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

## Contact

Visit us in [ircs://irc.libera.chat:6697](ircs://irc.libera.chat:6697), 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](/user/thebonsai/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.