[](bash4) \~\~DISCUSSION:off\~\~ # The Bash Hackers Wiki ![](keywords>bash shell linux scripting) Come visit us at #bash ! \~ormaaj \ 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 \<\>. [What would YOU like to see here?](wishes) (outdated and locked, please use the discussions) **Stranger!** [Feel free to register](http://wiki.bash-hackers.org/start&do=register) and comment or edit the contents. There is a [Bash Hackers Wiki needs love page](/meta/need_love) that lists some things to do. The registration is only there to prevent SPAM. \ ## 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(1)](/howto/edit-ed) - [Collapsing Functions](/howto/collapsing_functions) - [Illustrated Redirection Tutorial](/howto/redirection_tutorial) - [Calculate with dc(1)](/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]{.underline}*** **[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]{.underline}*** **[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\ Alt Type \Commands that set and query attributes/types, and manipulate simple datastructures.\ --------------------------------------------------------------------------------------------------------------------------------------- ------------------------------------------------------------------------------------------------------ -------------- ----------------- [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 I/O\ Alt Type \Commands for reading/parsing input, or producing/formatting output of standard streams.\ [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\ Alt Type \Commands that modify shell behavior, change special options, assist in debugging.\ [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\ Alt Type \Commands that operate on data and/or affect control flow.\ ------------------------------------------------------------------------------------------------------------- -------------------------------------------------------- -------- ----------------- [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\ Alt Type \Commands related to jobs, signals, process groups, subshells.\ [exec](/commands/builtin/exec) Replace the current shell process or set redirections. \- special builtin [exit](/commands/builtin/exit) Exit the shell. \- special builtin [kill](/commands/builtin/kill) Send a signal to specified process(es) \- builtin [trap](/commands/builtin/trap) Set signal handlers or output the current handlers. \- special builtin [times](/commands/builtin/times) Display process times. \- special builtin [wait](/commands/builtin/wait) Wait for background jobs and asynchronous lists. \- builtin Alt Type ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- \ \\ \ previous alphabetical version \ A-G -------------------------------------- ------------------------------------------------------------------------------------------------------ [caller](/commands/builtin/caller) identify/print execution frames (Bash builtin) [coproc](/syntax/keywords/coproc) Co-processes (Bash keyword) [declare](/commands/builtin/declare) display or set shell variables or functions along with attributes (Bash builtin, synonym: `typeset`) [exec](/commands/builtin/exec) replace the shell, set redirections (Bash builtin) I-N [let](/commands/builtin/let) arithmetic evaluation - an old fashioned way (Bash builtin) [mapfile](/commands/builtin/mapfile) Mapping lines of input to an array, also named `readarray` (Bash builtin) \ \ O-T ---------------------------------------- ------------------------------------------------------------------ [printf](/commands/builtin/printf) \"advanced `echo`\" (Bash builtin) [read](/commands/builtin/read) getting input from `stdin` (Bash builtin) [readonly](/commands/builtin/readonly) mark variables or functions as read-only (Bash builtin) [set](/commands/builtin/set) control positional parameters and shell behaviour (Bash builtin) [shopt](/commands/builtin/shopt) set/get shell options (Bash builtin) [test](/commands/classictest) the classic `test` command (Bash builtin) U-Z [unset](/commands/builtin/unset) unset variables and functions (Bash 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**: ([archives](http://mail.gnu.org/pipermail/bug-bash)) - **General questions**: ([archives](http://mail.gnu.org/pipermail/help-bash)) - Official Bash git repository: - **Browse**: [cgit](http://git.savannah.gnu.org/cgit/bash.git) - **Clone**: // ssh://git.sv.gnu.org/srv/git/bash.git • // ssh://git.sv.gnu.org/srv/git/bash.git • // http://git.savannah.gnu.org/r/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 \
## Most wanted Statistics for Month: **April 2012** -------------------------------------- ------- ------------------------------------------------------------ Rank Views Article 1 6833 [getopts_tutorial](/howto/getopts_tutorial) (March: 11663) 2 4025 [printf](/commands/builtin/printf) (March: 7079) 3 2861 [quoting](/syntax/quoting) (March: 5730) 4 2854 [classictest](/commands/classictest) (March: 6145) 5 2222 [pe](/syntax/pe) (March: 4540) 6 1760 [posparams](/scripting/posparams) (March: 3591) 7 1249 [bash4](bash4) (March: \--) 8 1212 [edit-ed](/howto/edit-ed) (March: 2727) 9 1205 [read](/commands/builtin/read) (March: \--) 10 1182 [mutex](/howto/mutex) (March: \--) - \"Total visits\": 35144 - The overall \"start\" page is not counted \ ## Contact \ Visit us in , 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 \ \ ![](contact>subj=Wiki reader feedback) \ \\