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The Bash Hackers Wiki
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<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 (outdated and locked, please use the discussions)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
- Bash v4 - a rough overview (unmaintained, since Bash 4 is more or less standard)
- style -- an assorted collection of style and optic hints
- basics
- newbie_traps
- bashbehaviour
- posparams
- processtree
- obsolete
- nonportable
- debuggingtips
- terminalcodes
- tutoriallist
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:
- Simple locking (against parallel run)
- Rudimentary config files for your scripts
- Editing files with ed(1)
- Collapsing Functions
- Illustrated Redirection Tutorial
- Calculate with dc(1)
- Introduction to pax - the POSIX archiver
- getopts_tutorial (under construction!)
- dissectabadoneliner 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
- Bash features overview by version
- Basic grammar rules
- Quoting and character escaping
- Parsing and execution
- Some words about words...
- Patterns and pattern matching
- Arithmetic expressions
- List of shell options
- Redirection
- Special parameters and shell variables
- Arrays
<WRAP column 40%> [Compound commands]{.underline}
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
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<WRAP column 40%> [Expansions and substitutions]{.underline}
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
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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.
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Declaration commands\ Alt Type
\<wrap center round lo todo box 80%\>Commands that set and query attributes/types, and manipulate simple datastructures.\</wrap\>
[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
<wrap center round lo todo box 80%>Commands for reading/parsing input, or producing/formatting output of standard streams.</wrap>
[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
\<wrap center round lo todo box 80%\>Commands that modify shell behavior, change special options, assist in debugging.\</wrap\>
[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
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Control flow and data processing\ Alt Type
\<wrap center round lo todo box 80%\>Commands that operate on data and/or affect control flow.\</wrap\>
[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
<wrap center round lo todo box 80%>Commands related to jobs, signals, process groups, subshells.</wrap>
[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
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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)
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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)
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Dictionary
<note tip>A list of expressions, words, and their meanings is here.</note>
Links
Official Bash links
- Chet Ramey's Bash page and its FAQ.
- GNU Bash software page
- 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(r) 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.
- The Single Unix Specification (version 4, aka POSIX-2008)
- The Austin Group - List archives, Bug tracker
- comp.unix.shell FAQ
- Advanced Bash-Scripting Guide - last update: 10 Mar 2014, but still very useful guide.
Documentation / Reference
- Bash: man page info page
- AT&T ksh: ksh88 ksh93
- mksh (pdksh successor)
- zsh
- dash
- Heirloom Bourne shell
- Thompson shell
Assorted interesting links
- History and development of the traditional Bourne shell family - very interesting and nice to read!
- Interview with Chet Ramey
- Interview with Steve Bourne • Stephen Bourne - BSDCan 2015 keynote
- Interview with David Korn
- Kernighan on the Unix pipeline (computerphile video)
- 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
- Bashphorism list from the Bash IRC channel on Freenode
- Some more or less funny commandline stuff
- How to Enable SSH on Ubuntu Tutorial
- How To Make an Awesome Custom Shell with ZSH
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
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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
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Contact
<WRAP column 40%> Visit us in 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 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
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- you found mistakes / bugs
Simply: Reader's feedback </WRAP>
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