Bash (Unix shell)

Bash, short for Bourne-Again SHell, is a shell program and command language supported by the Free Software Foundation^[2] and first developed for the GNU Project^[3] by Brian Fox.^[4] Designed as a 100%^[5] free software alternative for the Bourne shell,^[6][7][8] it was initially released in 1989.^[9] Its moniker is a play on words, referencing both its predecessor, the Bourne shell,^[10] and the concept of rebirth.^[11][12]

Bash

Screenshot of a Bash session
Original author(s)	Brian Fox
Developer(s)	Chet Ramey
Initial release	8 June 1989; 35 years ago (8 June 1989)
Stable release	5.2.37[1]  / 23 September 2024
Repository	git.savannah.gnu.org/gitweb/?p=bash.git
Written in	C
Operating system	BeOS Haiku macOS ( GPL-2.0-or-later ; GPL-3.0-or-later through 3rd parties) Unix-like Windows ( GPL-3.0-or-later )
Platform	GNU
Available in	Multilingual (gettext)
Type	Shell (computing), Unix shell, command language
License	Since 4.0: GPL-3.0-or-later, 1.11? to 3.2: GPL-2.0-or-later, 0.99? to 1.05?: GPL-1.0-or-later
Website	www.gnu.org/software/bash/

Since its inception, Bash has gained widespread adoption and is commonly used as the default login shell for numerous Linux distributions. It holds historical significance as one of the earliest programs ported to Linux by Linus Torvalds, alongside the GNU Compiler (GCC).^[13] It is available on nearly all modern operating systems, making it a versatile tool in various computing environments.

As a command processor, Bash operates within a text window where users input commands to execute various tasks. It also supports the execution of commands from files, known as shell scripts, facilitating automation. In keeping with Unix shell conventions, Bash incorporates a rich set of features. The keywords, syntax, dynamically scoped variables and other basic features of the language are all copied from the Bourne shell, sh. Other features, e.g., history, are copied from the C shell, csh, and the Korn Shell, ksh. Bash is a POSIX-compliant shell with a number of extensions.

History

While Bash was developed for UNIX and UNIX-like operating systems such as GNU/Linux,^[14] it is also available on Windows, BeOS,^[15][16] and Haiku.^[17]

Brian Fox began coding Bash on January 10, 1988,^[18] after Richard Stallman became dissatisfied with the lack of progress being made by a prior developer.^[7] Stallman and the FSF considered a free shell that could run existing shell scripts so strategic to a completely free system built from BSD and GNU code that this was one of the few projects they funded themselves, with Fox undertaking the work as an employee of FSF.^[7][19] Fox released Bash as a beta, version .99, on June 8, 1989,^[9] and remained the primary maintainer until sometime between mid-1992^[20] and mid-1994,^[21] when he was laid off from FSF^[22] and his responsibility was transitioned to another early contributor, Chet Ramey.^{[23][24][25][26][27]}

Since then, Bash has become by far the most popular shell among users of Linux, becoming the default interactive shell on that operating system's various distributions^[28][29] and on Apple's macOS releases before Catalina in October 2019.^[30][31][32] Bash has also been ported to Microsoft Windows^[33][34] and distributed with Cygwin and MinGW, to DOS by the DJGPP project, to Novell NetWare, to OpenVMS by the GNU project,^[35] to ArcaOS,^[36] and to Android via various terminal emulation applications.

In September 2014, Stéphane Chazelas, a Unix/Linux specialist,^[37] discovered a security bug in the program. The bug, first disclosed on September 24, was named Shellshock and assigned the numbers CVE-2014-6271, CVE-2014-6277 and CVE-2014-7169. The bug was regarded as severe, since CGI scripts using Bash could be vulnerable, enabling arbitrary code execution. The bug was related to how Bash passes function definitions to subshells through environment variables.^[38]

Features

As a command processor, Bash operates within a text window where users input commands to execute various tasks. It also supports the execution of commands from files, known as shell scripts, facilitating automation. In keeping with Unix shell conventions, Bash incorporates a rich set of features, including:

• Invocation as a...
  • Interactive shell,
  • Non-interactive shell, or
  • Login shell;
• A command-line interface;
• Exit status codes;
• Control structures for
  • Condition testing,
    • if, case, select,
    • logical AND (&&) and OR (||), and
  • Iteration
    • for, while, until loops, and
    • Arithmetic C-style loop: for ((;
• Syntaxes for file type, string value and integer value testing
  • Traditional single bracket test: [,
  • Modern double bracket test: [[ ... ]], including
    • Extended regular expression and extglob matching
    • Lexicographic sorting with < and >;
• UNIX-style pipelines: |;
• Subshells: ( ... );
• Signaling as a means of inter-process communication using the trap builtin;
• Asynchronous execution: job_spec &;
• A shell portability mode where commands can be interpreted in conformance with the POSIX standard;
• Command parsing:
  • Comments are ignored:
    • Bourne-style # hashtag comments, and
    • Thompson-style : colon comments;
  • Commands are parsed one line at a time,
    • Control structures are honored, and
    • Backslash \ escapes are also honored at the ends of lines,
  • Split into words (i.e., word splitting) according to quoting rules,
    • Including ANSI-C quoting $'...', and
  • Seven kinds of expansions are performed on the resulting string in the following order:
    • (Step 1) Brace expansion kernel{-headers},
    • (Step 2) Tilde expansion ~,
    • (Step 3) In a left-to-right fashion:
      • Parameter and variable expansion $foo or ${bar}, including
        • Dynamically scoped variables,
        • Indexed arrays of unlimited size,
        • Associative arrays via declare -A, and
        • Expansion syntaxes which can perform some tasks more quickly than external utilities, such as
          • Pattern Substitution
            • ${foo//x/y} for sed 's/x/y/g',
          • Remove Matching Prefix or Suffix Pattern
            • ${bar##[a-zA-Z0-9]*} for cut -c8-,
          • Print Array Keys
            • ${!array[@]}, and
          • Display Error if Null or Unset
            • ${var:?error message}, among others,
      • Command substitution: $( ... ),
      • Process substitution, <() or >(), when a system supports it:
      • Arithmetic expansion, (( ... )) or $(( ... )), including
        • Integer arithmetic in any base from two to sixty-four, although
        • Floating-point arithmetic is not available from within the shell itself (for this functionality, see current versions of bc and awk, among others),
    • (Step 4) Word splitting (again),
    • (Step 5) Pathname expansion,
      • Meaning shell-style globbing and pattern matching using *, ?, [...], and
    • Quote removal;
  • Redirections of Standard Input, Standard Output and Standard Error data streams are performed, including
    • File writing, >, and appending, >>,
    • Here documents, <<,
    • Here strings, <<<, which allow parameters to be used as input, and
    • A redirection operator, >|, which can force overwriting of a file when a shell's "noclobber" setting is enabled;
  • Command name lookup is performed, in the following order:
    • Commands internal to the shell:
      • Shell aliases,
      • Shell reserved words,
      • Shell functions, and
      • Shell built-in commands;
    • Commands external to the shell:
      • Separate UNIX-style programs such as ls or ln, and
      • Shell scripts, which are files containing executable commands. (Shell scripts do not require compilation before execution and, when certain requirements are met, can be invoked as commands by using their filename.)
  • The resulting string is executed as a command.

Bash also offers...

• Configurable execution environment(s):^[39]
  • Shell and session startup files such as ~/.bashrc and ~/.profile (i.e., dotfiles);
• Settings (set built-in) and shell options (shopt built-in) which alter shell behavior;
• With interactive invocation only,
  • Unlimited size command history,
  • Jobs and job control,
  • A directory stack (see pushd and popd built-ins),
  • Tab completion,
  • Configurable prompts, and
  • Command line editing with GNU readline;
• Lightweight logging for debugging purposes (xtrace), and other lightweight debugging options (errexit, noexec, nounset, pipefail, etc.);
• Shell compatibility modes: bash 5.1 can operate as if it were bash 4.2, etc.;
• Documentation:
  • A built-in help command,
  • A man page, and
  • An info page which is the same as the GNU manual;
• Informal avenues of support via:
  • IRC at libera.chat #bash
  • Mailing lists at https://www.gnu.org/software/bash/

The keywords, syntax, dynamically scoped variables and other basic features of the language are all copied from sh. Other features, e.g., history, are copied from csh and ksh.

The Bash command syntax is a superset of the Bourne shell command syntax. Bash supports brace expansion,^[40] command line completion (Programmable Completion),^[41] basic debugging^[42][43] and signal handling (using trap) since bash 2.05a^[44][45] among other features. Bash can execute the vast majority of Bourne shell scripts without modification, with the exception of Bourne shell scripts stumbling into fringe syntax behavior interpreted differently in Bash or attempting to run a system command matching a newer Bash builtin, etc. Bash command syntax includes ideas drawn from the Korn Shell (ksh) and the C shell (csh) such as command line editing, command history (history command),^[46] the directory stack, the $RANDOM and $PPID variables, and POSIX command substitution syntax $(...).

When a user presses the tab key within an interactive command-shell, Bash automatically uses command line completion, since beta version 2.04,^[47] to match partly typed program names, filenames and variable names. The Bash command-line completion system is very flexible and customizable, and is often packaged with functions that complete arguments and filenames for specific programs and tasks.

Bash's syntax has many extensions lacking in the Bourne shell. Bash can perform integer calculations ("arithmetic evaluation") without spawning external processes. It uses the ((...)) command and the $((...)) variable syntax for this purpose. Its syntax simplifies I/O redirection. For example, it can redirect standard output (stdout) and standard error (stderr) at the same time using the &> operator. This is simpler to type than the Bourne shell equivalent 'command > file 2>&1'. Bash supports process substitution using the <(command) and >(command)syntax, which substitutes the output of (or input to) a command where a filename is normally used. (This is implemented through /proc/fd/ unnamed pipes on systems that support that, or via temporary named pipes where necessary).

When using the 'function' keyword, Bash function declarations are not compatible with Bourne/Korn/POSIX scripts (the KornShell has the same problem when using 'function'), but Bash accepts the same function declaration syntax as the Bourne and Korn shells, and is POSIX-conformant. Because of these and other differences, Bash shell scripts are rarely runnable under the Bourne or Korn shell interpreters unless deliberately written with that compatibility in mind, which is becoming less common as Linux becomes more widespread. But in POSIX mode, Bash conforms with POSIX more closely.^[48]

Bash supports here documents. Since version 2.05b Bash can redirect standard input (stdin) from a "here string" using the <<< operator.

Bash 3.0 supports in-process regular expression matching using a syntax reminiscent of Perl.^[49]

In February 2009,^[50] Bash 4.0 introduced support for associative arrays.^[51] Associative array indices are strings, in a manner similar to AWK or Tcl.^[52] They can be used to emulate multidimensional arrays. Bash 4 also switches its license to GPL-3.0-or-later; some users suspect this licensing change is why macOS continues to use older versions.^[53] Zsh became the default shell in macOS with the release of macOS Catalina in 2019.^[54]

Brace expansion

Brace expansion, also called alternation, is a feature copied from the C shell. It generates a set of alternative combinations. Generated results need not exist as files. The results of each expanded string are not sorted and left to right order is preserved:

$ echo a{p,c,d,b}e
ape ace ade abe
$ echo {a,b,c}{d,e,f}
ad ae af bd be bf cd ce cf

Users should not use brace expansions in portable shell scripts, because the Bourne shell does not produce the same output.

$ # bash shell
$/bin/bash -c 'echo a{p,c,d,b}e'
ape ace ade abe
$ # A traditional shell does not produce the same output
$ /bin/sh -c 'echo a{p,c,d,b}e'
a{p,c,d,b}e

When brace expansion is combined with wildcards, the braces are expanded first, and then the resulting wildcards are substituted normally. Hence, a listing of JPEG and PNG images in the current directory could be obtained using:

ls *.{jpg,jpeg,png}    # expands to *.jpg *.jpeg *.png - after which,
                       # the wildcards are processed
echo *.{png,jp{e,}g}   # echo just shows the expansions -
                       # and braces in braces are possible.

In addition to alternation, brace expansion can be used for sequential ranges between two integers or characters separated by double dots. Newer versions of Bash allow a third integer to specify the increment.

$ echo {1..10}
1 2 3 4 5 6 7 8 9 10
$ echo {01..10}
01 02 03 04 05 06 07 08 09 10
$ echo file{1..4}.txt
file1.txt file2.txt file3.txt file4.txt
$ echo {a..e}
a b c d e
$ echo {1..10..3}
1 4 7 10
$ echo {a..j..3}
a d g j

When brace expansion is combined with variable expansion (A.K.A. parameter expansion and parameter substitution) the variable expansion is performed after the brace expansion, which in some cases may necessitate the use of the eval built-in, thus:

$ start=1; end=10
$ echo {$start..$end} # fails to expand due to the evaluation order
{1..10}
$ eval echo {$start..$end} # variable expansion occurs then resulting string is evaluated
1 2 3 4 5 6 7 8 9 10

Startup scripts

When Bash starts, it executes the commands in a variety of dot files. Unlike Bash shell scripts, dot files do typically have neither the execute permission enabled nor an interpreter directive like #!/bin/bash.

Legacy-compatible Bash startup example

The example ~/.bash_profile below is compatible with the Bourne shell and gives semantics similar to csh for the ~/.bashrc and ~/.bash_login. The [ -r filename ] && cmd is a short-circuit evaluation that tests if filename exists and is readable, skipping the part after the && if it is not.

[ -r ~/.profile ] && . ~/.profile             # set up environment, once, Bourne-sh syntax only
if [ -n "$PS1" ] ; then                       # are we interactive?
   [ -r ~/.bashrc     ] && . ~/.bashrc        # tty/prompt/function setup for interactive shells
   [ -r ~/.bash_login ] && . ~/.bash_login    # any at-login tasks for login shell only
fi                                            # End of "if" block

Operating system issues in Bash startup

Some versions of Unix and Linux contain Bash system startup scripts, generally under the /etc directory. Bash executes these files as part of its standard initialization, but other startup files can read them in a different order than the documented Bash startup sequence. The default content of the root user's files may also have issues, as well as the skeleton files the system provides to new user accounts upon setup. The startup scripts that launch the X window system may also do surprising things with the user's Bash startup scripts in an attempt to set up user-environment variables before launching the window manager. These issues can often be addressed using a ~/.xsession or ~/.xprofile file to read the ~/.profile — which provides the environment variables that Bash shell windows spawned from the window manager need, such as xterm or Gnome Terminal.

Portability

Invoking Bash with the --posix option or stating set -o posix in a script causes Bash to conform very closely to the POSIX 1003.2 standard.^[55] Bash shell scripts intended for portability should take into account at least the POSIX shell standard. Some bash features not found in POSIX are:^[55][56]

• Certain extended invocation options
• Brace expansion
• Arrays and associative arrays
• The double bracket [[...]] extended test construct and its regex matching
• The double-parentheses arithmetic-evaluation construct (only (( ... )); $(( ... )) is POSIX)
• Certain string-manipulation operations in parameter expansion
• local for scoped variables
• Process substitution
• Bash-specific builtins
• Coprocesses
• $EPOCHSECONDS and $EPOCHREALTIME variables^[57]

If a piece of code uses such a feature, it is called a "bashism" – a problem for portable use. Debian's checkbashisms and Vidar Holen's shellcheck can be used to make sure that a script does not contain these parts.^[58][59] The list varies depending on the actual target shell: Debian's policy allows some extensions in their scripts (as they are in the dash shell),^[56] while a script intending to support pre-POSIX Bourne shells, like autoconf's configure, are even more limited in the features they can use.^[60]

Keyboard shortcuts

Main article: GNU Readline

Bash uses GNU Readline to provide keyboard shortcuts for command line editing using the default ( Emacs ) key bindings. Vi-bindings can be enabled by running set -o vi.^[61]

Process management (Job control)

The Bash shell has two modes of execution for commands: batch (asynchronous), and concurrent (synchronous).

To execute commands in batch mode (i.e., in sequence) they must be separated by the character ";", or on separate lines:

command1; command2
command3

In this example, when command1 is finished, command2 is executed, and when command2 has completed, command3 will execute.

A background execution of command1 can occur using (symbol &) at the end of an execution command, and process will be executed in background while immediately returning control to the shell and allowing continued execution of commands.

command1 &

Or to have a concurrent execution of command1 and command2, they must be executed in the Bash shell in the following way:

command1 & command2

In this case command1 is executed in the background & symbol, returning immediately control to the shell that executes command2 in the foreground.

A process can be stopped and control returned to bash by typing Ctrl+z while the process is running in the foreground.^[62]

A list of all processes, both in the background and stopped, can be achieved by running jobs:

$ jobs
[1]-  Running                  command1 &
[2]+  Stopped                  command2

In the output, the number in brackets refers to the job id. The plus sign signifies the default process for bg and fg. The text "Running" and "Stopped" refer to the process state. The last string is the command that started the process.

The state of a process can be changed using various commands. The fg command brings a process to the foreground, while bg sets a stopped process running in the background. bg and fg can take a job id as their first argument, to specify the process to act on. Without one, they use the default process, identified by a plus sign in the output of jobs. The kill command can be used to end a process prematurely, by sending it a signal. The job id must be specified after a percent sign:

kill %1

Conditional execution

Bash supplies "conditional execution" command separators that make execution of a command contingent on the exit code set by a precedent command. For example:

cd "$SOMEWHERE" && ./do_something || echo "An error occurred" >&2

Where ./do_something is only executed if the cd (change directory) command was "successful" (returned an exit status of zero) and the echo command would only be executed if either the cd or the ./do_something command return an "error" (non-zero exit status).

For all commands the exit status is stored in the special variable $?. Bash also supports if ...;then ...;else ...;fi and case $VARIABLE in $pattern)...;;$other_pattern)...;; esac forms of conditional command evaluation.

Bug reporting

"bashbug" redirects here. For the widely reported September 2014 bug found in Bash, see Shellshock (software bug).

An external command called bashbug reports Bash shell bugs. When the command is invoked, it brings up the user's default editor with a form to fill in. The form is mailed to the Bash maintainers (or optionally to other email addresses).^[63][64]

Programmable completion

Bash supports programmable completion via built-in complete, compopt, and compgen commands.^[65] The feature has been available since the beta version of 2.04 released in 2000.^[66][67] These commands enable complex and intelligent completion specification for commands (i.e. installed programs), functions, variables, and filenames.^[68]

The complete and compopt two commands specify how arguments of some available commands or options are going to be listed in the readline input. As of version 5.1 completion of the command or the option is usually activated by the Tab ↹ keystroke after typing its name.^[68]

Program name

The program's name is a figure of speech or witticism which begins with an homage to Stephen Bourne, the creator of one of the shell programs which have sometimes been considered superseded by the bash shell. His name is used as a pun on the image of childbirth. With that pun, it would seem, is added an allusion: possibly to the Hindu or Buddhist idea of reincarnation; possibly to the Christian idiom known as "being born again;" or quite possibly just to the more abstract idea of renewal. While numerous English translations of the Christian New Testament, Book of John, chapter 3 do contain the words "born again," Merriam-Webster's dictionary has "born-again" defined as a "...person who has made a renewed or confirmed commitment....^[69]" Whatever the original touchstone may have been, in the end the program received the name, "the Bourne Again SHell."^[70][71]

The acronym of that name then is "bash," a word meaning "to strike violently.^[72]" In the context of computer programming, to "violently hit something," such as a computer keyboard, could be considered a hyperbolic image of some frustration. Such imagery of negative emotionality could be seen as standing in direct juxtaposition to the idea of becoming "born again."

The naming could be considered an instance of verbal irony^[73] or accidental innuendo.^[74] Bash grammar was initially based on the grammars of the most popular Unix shell programs then currently in use, some of which were considered particularly difficult to use or frustrating at that time. As the years progressed, bash development has made its grammar more user-friendly,^{[75][76][77][78][79][80]} so much so that it seems likely that the bash project has been committed to improving its usability. Since then, bash has become the de facto default shell program in most Linux and Unix operating systems.

Documentation

As the standard upon which bash is based, the POSIX, or IEEE Std 1003.1,^[81] et seq, is informative.

The Linux man page^[82][83] is intended to be the authoritative explanatory document for the understanding of how bash operates, while the GNU manual is sometimes considered more user-friendly for reading. "You may also find information about Bash by running info bash ... or by looking at /usr/share/doc/bash/, /usr/local/share/doc/bash/, or similar directories on your system. A brief summary is available by running bash --help.^[70]"

On modern Linuxes, information on shell built-in commands can be found by executing help, help [built-in name]or man builtins at a terminal prompt where bash is installed. Some commands, such as echo, false, kill, printf, test or true, depending on your system and on your locally installed version of bash, can refer to either a shell built-in or a system binary executable file. When one of these command name collisions occurs, bash will by default execute a given command line using the shell built-in. Specifying a binary executable's absolute path (i.e., /bin/printf) is one way of ensuring that the shell uses a system binary. This name collision issue also effects any "help summaries" viewed with kill --help and /bin/kill --help. Shell built-ins and system binary executable files of the same name often have differing options.

"The project maintainer also has a Bash page which includes Frequently Asked Questions",^[84][85][70] this FAQ is current as of bash version 5.1 and is no longer updated.

Vulnerabilities

A security hole in Bash dating from version 1.03 (August 1989),^[86] dubbed Shellshock, was discovered in early September 2014 and quickly led to a range of attacks across the Internet.^[87][88][89] Patches to fix the bugs were made available soon after the bugs were identified.

Licensing

Since 4.0: GPL-3.0-or-later ^[90]

1.11? to 3.2: GPL-2.0-or-later ^[91]

0.99? to 1.05?: GPL-1.0-or-later ^{[92] [51] [93]}

Versions

A version is also available for Windows 10 and Windows 11 via the Windows Subsystem for Linux.^[94][95] It is also the default user shell in Solaris 11.^[96] Bash was also the default shell in BeOS,^[15] and in versions of Apple macOS from 10.3 (originally, the default shell was tcsh) to 10.15 (macOS Catalina), which changed the default shell to zsh,^[32] although Bash remains available as an alternative shell.^[54]

Release history

Version	Release date	Release notes
bash-5.2.15	2022-12-13	NEWS
bash-5.2	2022-09-26
bash-5.1	2020-12-07	github version history NEWS [51]
bash-5.0	2019-01-07	[97][98][99]
bash-5.0-rc1	2018-12-20
bash-5.0-beta2	2018-11-28
bash-5.0-beta	2018-09-17
bash-5.0-alpha	2018-05-22
bash-4.4	2016-09-15	github version history NEWS v4.4
bash-4.4-rc2	2016-08-22
bash-4.4-rc1	2016-02-24
bash-4.4-beta2	2016-07-11
bash-4.4-beta	2015-10-12
bash-4.3	2014-02-26
bash-4.2	2011-02-13
bash-4.1	2009-12-31
bash-4.0	2009-02-20
bash-4.0-rc1	2009-01-12
bash-3.2	2006-10-11
bash-3.1	2005-12-08
bash-3.0	2004-08-03
bash-2.05b	2002-07-17
bash-2.05a	2001-11-16
bash-2.05	2001-04-09
bash-2.04	2000-03-21
bash-2.03	1999-02-19
bash-2.02	1998-04-18
bash-2.01	1997-06-05
bash-2.0	1996-12-31

See also

• Free and open-source software portal

• Comparison of command shells

References

1. https://ftp.gnu.org/gnu/bash/. {{cite web}}: Missing or empty |title= (help)
2. "Free Software Foundation — working together for free software — Front Page". fsf.org. Retrieved 19 May 2024. The Free Software Foundation (FSF) is a nonprofit with a worldwide mission to promote computer user freedom.
3. "GNU in a Nutshell". gnu.org. Retrieved 19 May 2024. The ultimate goal is to provide free software to do all of the jobs computer users want to do—and thus make proprietary software a thing of the past.
4. "GNU's Bulletin, vol. 1 no. 7, June, 1989 :: GNU's Who". gnu.org. Retrieved 19 May 2024. Brian Fox has now completed GNU's version of sh, called BASH, the `Bourne Again SHell'.
5. "GNU Software". gnu.org. Retrieved 19 May 2024. GNU is an operating system which is 100% free software.
6. "Bourne shell". ibm.com. Retrieved 19 May 2024. The Bourne shell is an interactive command interpreter and command programming language.
7. Richard Stallman (forwarded with comments by Chet Ramey) (10 February 1988). "GNU + BSD = ?". Newsgroup: comp.unix.questions. Usenet: [e-mail]. Archived from the original on 28 December 2021. Retrieved 28 December 2021. For a year and a half, the GNU shell was "just about done". The author made repeated promises to deliver what he had done, and never kept them. Finally I could no longer believe he would ever deliver anything. So Foundation staff member Brian Fox is now implementing an imitation of the Bourne shell.
8. Hamilton, Naomi (30 May 2008), "The A-Z of Programming Languages: BASH/Bourne-Again Shell", Computerworld: 2, archived from the original on 6 July 2011, retrieved 21 March 2011, When Richard Stallman decided to create a full replacement for the then-encumbered Unix systems, he knew that he would eventually have to have replacements for all of the common utilities, especially the standard shell, and those replacements would have to have acceptable licensing. NOTE: Original computerworld.com.au link is dead: see also copies of original material at

   • readthedocs.io,
   • computerworld.com.au and
   • the University of South Carolina.
9. Brian Fox (forwarded by Leonard H. Tower Jr.) (8 June 1989). "Bash is in beta release!". Newsgroup: gnu.announce. Archived from the original on 4 May 2013. Retrieved 28 October 2010.
10. "I Almost Get a Linux Editor and Compiler". Dr. Dobb's. Archived from the original on 2 March 2021. Retrieved 12 September 2020.
11. Richard Stallman (12 November 2010). "About the GNU Project". Free Software Foundation. Archived from the original on 24 April 2011. Retrieved 13 March 2011. "Bourne Again Shell" is a play on the name Bourne Shell, which was the usual shell on Unix.
12. Gattol, Markus (13 March 2011), Bourne-again Shell, archived from the original on 9 March 2011, retrieved 13 March 2011, The name is a pun on the name of the Bourne shell (sh), an early and important Unix shell written by Stephen Bourne and distributed with Version 7 Unix circa 1978, and the concept of being "born again".
13. Torvalds, Linus Benedict (August 1991). "comp.os.minix". Retrieved 6 September 2009. I've currently ported bash(1.08) and gcc(1.40), and things seem to work.
14. "Bash FAQ, version 4.14". Archived from the original on September 1, 2018. Retrieved April 9, 2016.
15. "A desktop alternative". Forbes.
16. "Appendix A: Using the BeOS Command Line Shell". testou.free.fr.
17. "Terminal".
18. Brian Fox (29 August 1996), shell.c, Free Software Foundation, archived from the original on 28 September 2018, retrieved 1 November 2010, Birthdate: Sunday, January 10th, 1988. Initial author: Brian Fox
19. Richard Stallman (3 October 2010). "About the GNU Project". Free Software Foundation. Archived from the original on 24 April 2011. Retrieved 21 March 2011. Free Software Foundation employees have written and maintained a number of GNU software packages. Two notable ones are the C library and the shell. ... We funded development of these programs because the GNU Project was not just about tools or a development environment. Our goal was a complete operating system, and these programs were needed for that goal.
20. len ([e-mail]) (20 April 1993). "January 1993 GNU's Bulletin". Newsgroup: gnu.announce. Usenet: [e-mail]. Archived from the original on 2 March 2021. Retrieved 28 October 2010.
21. Ramey, Chet (1 August 1994). "Bash - the GNU shell (Reflections and Lessons Learned)". Linux Journal. Archived from the original on 5 December 2008. Retrieved 13 November 2008.
22. Chet Ramey (31 October 2010), Dates in your Computerworld interview, archived from the original on 20 July 2012, retrieved 31 October 2010
23. Hamilton, Naomi (30 March 2008). "The A-Z of Programming Languages: BASH/Bourne-Again Shell". Computerworld. Archived from the original on 8 November 2016. Retrieved 1 March 2022.
24. Ramey, Chet (20 April 2021). "The GNU Bourne-Again Shell". Technology Infrastructure Services. Case Western Reserve University. Retrieved 1 March 2022.
25. Chet Ramey (12 June 1989). "Bash 0.99 fixes & improvements". Newsgroup: gnu.bash.bug. Archived from the original on 10 November 2012. Retrieved 1 November 2010.
26. Chet Ramey (24 July 1989). "Some bash-1.02 fixes". Newsgroup: gnu.bash.bug. Archived from the original on 10 November 2012. Retrieved 30 October 2010.
27. Brian Fox (2 March 1990). "Availability of bash 1.05". Newsgroup: gnu.bash.bug. Archived from the original on 10 November 2012. Retrieved 30 October 2010.
28. Bresnahan, Christine; Blum, Richard (April 2015). CompTIA Linux+ Powered by Linux Professional Institute Study Guide: Exam LX0-103 and Exam LX0-104 (3rd ed.). John Wiley & Sons, Inc. p. 5. ISBN 978-1-119-02122-3. Archived from the original on 2 March 2021. Retrieved 6 June 2016. In Linux, most users run bash because it is the most popular shell.
29. Danesh, Arman; Jang, Michael (February 2006). Mastering Linux. John Wiley & Sons, Inc. p. 363. ISBN 978-0-7821-5277-7. Archived from the original on 2 March 2021. Retrieved 6 June 2016. The Bourne Again Shell (bash) is the most common shell installed with Linux distributions.
30. Foster-Johnson, Eric; Welch, John C.; Anderson, Micah (April 2005). Beginning Shell Scripting. John Wiley & Sons, Inc. p. 6. ISBN 978-0-7645-9791-6. Archived from the original on 2 March 2021. Retrieved 6 June 2016. Bash is by far the most popular shell and forms the default shell on Linux and Mac OSX systems.
31. "Use zsh as the default shell on your Mac - Apple Support". Archived from the original on 2 December 2019. Retrieved 1 July 2019.
32. Warren, Tom (4 June 2019). "Apple replaces bash with zsh as the default shell in macOS Catalina". The Verge. Archived from the original on 10 June 2019. Retrieved 13 June 2019.
33. "Missing source code - GPL compliance? · Issue #107 · Microsoft/WSL". GitHub. Archived from the original on 24 September 2019. Retrieved 8 July 2016.
34. "GNU Bash". Softpedia. SoftNews. 23 January 2010. Archived from the original on 21 October 2017. Retrieved 9 April 2016.
35. "Installing the new GNU packages". Archived from the original on 3 October 2020. Retrieved 4 September 2020.
36. "Compatibility Subsystems". Archived from the original on 23 September 2020. Retrieved 4 September 2020.
37. Juliana, Cino (10 June 2017). "Linux bash exit status and how to set exit status in bash - Techolac". Archived from the original on 21 June 2019. Retrieved 21 June 2019.
38. Huzaifa Sidhpurwala (24 September 2014). "Bash specially-crafted environment variables code injection attack". Red Hat. Archived from the original on 25 September 2014. Retrieved 25 September 2014.
39. "Command Execution Environment (Bash Reference Manual)". www.gnu.org.
40. "Brace Expansion (Bash Reference Manual)". www.gnu.org. Archived from the original on 15 March 2018. Retrieved 10 January 2024.
41. {{ cite web bash.html#Programmable-Completion | title = Bash Reference Manual | url = https://www.gnu.org/software/bash/manual/ }} | website = www.gnu.org
42. "Debugging Bash scripts". tldp.org. Archived from the original on 4 November 2018. Retrieved 20 November 2018.
43. "The Set Builtin (Bash Reference Manual)". www.gnu.org. Retrieved 10 January 2024.
44. "Bash changes [Bash Hackers Wiki (DEV 20200708T2203)]". wiki-dev.bash-hackers.org. Archived from the original on 23 September 2019. Retrieved 23 September 2019.
45. "Bourne Shell Builtins (Bash Reference Manual)". www.gnu.org. Retrieved 10 January 2024.
46. "Bash Reference Manual". www.gnu.org. Archived from the original on 15 September 2019. Retrieved 15 September 2019.
47. "Working more productively with bash 2.x/3.x". www.caliban.org. Archived from the original on 29 June 2018. Retrieved 21 June 2018.
48. "6.11 Bash POSIX Mode", The GNU Bash Reference Manual, for Bash, Version 4.1, 23 December 2009, archived from the original on 3 December 2010, retrieved 26 October 2010
49. "Advanced Bash-Scripting Guide". www.tldp.org. Section 37.2 (Bash, version 3). Archived from the original on 5 May 2017. Retrieved 5 March 2017.
50. "Bash, version 4". tldp.org. Archived from the original on 1 July 2018. Retrieved 25 June 2018.
51. "BashFAQ/061 - Greg's Wiki". mywiki.wooledge.org. Archived from the original on 2 March 2021. Retrieved 1 March 2021.
52. "Arrays (Bash Reference Manual)". www.gnu.org. Archived from the original on 11 July 2018. Retrieved 4 July 2018.
53. "macos - Update bash to version 4.0 on OSX". Ask Different. Archived from the original on 25 June 2018. Retrieved 25 June 2018.
54. Hughes, Matthew (4 June 2019). "Why does macOS Catalina use Zsh instead of Bash? Licensing". The Next Web. Archived from the original on 31 December 2020. Retrieved 12 January 2021.
55. Mendel Cooper. "Portability Issues". The Linux Documentation Project. ibiblio.org. Archived from the original on 27 January 2012. Retrieved 26 January 2012.
56. "10. Files". Debian Policy Manual v4.5.0.2. Archived from the original on 12 May 2020. Retrieved 11 May 2020.
57. "How To Format Date And Time In Linux, MacOS, And Bash?". Shell Tips!. Archived from the original on 3 June 2020. Retrieved 3 June 2020.
58. checkbashisms(1) – Linux General Commands Manual
59. shellcheck(1) – Linux General Commands Manual
60. "Portable Shell". Autoconf. Archived from the original on 2 March 2021. Retrieved 20 January 2020.
61. "BASH Help - A Bash Tutorial". Hypexr.org. 5 October 2012. Archived from the original on 2 March 2021. Retrieved 21 July 2013.
62. "Bash Reference Manual". www.gnu.org. Archived from the original on 15 March 2018. Retrieved 27 March 2018.
63. bashbug(1) Archived October 2, 2018, at the Wayback Machine, die.net
64. "Linux / Unix Command: bashbug" Archived October 6, 2014, at the Wayback Machine, apple.com
65. "Bash Reference Manual". tiswww.case.edu.
66. "Working more productively with bash 2.x/3.x". www.caliban.org. Archived from the original on 29 June 2018. Retrieved 21 June 2018.
67. "Index of /gnu/bash". ftp.swin.edu.au. Archived from the original on 8 March 2020. Retrieved 15 September 2019.
68. "An Introduction to Programmable Completion". tldp.org. Retrieved 21 January 2022.
69. "Definition of BORN-AGAIN". www.merriam-webster.com. Retrieved 9 January 2024.
70. "Bash - GNU Project - Free Software Foundation". www.gnu.org. Retrieved 10 January 2024.
71. "What is Bash? (Bash Reference Manual)". www.gnu.org. Retrieved 9 January 2024.
72. "Definition of BASH". www.merriam-webster.com. 5 January 2024. Retrieved 9 January 2024.
73. "Irony Definition, Common Examples, and Significance in Literature". 31 August 2020.
74. "Innuendo - Examples and Definition of Innuendo". 2 January 2014.
75. "BashGuide/Arrays - Greg's Wiki". mywiki.wooledge.org. Retrieved 10 January 2024.
76. "CommandSubstitution - Greg's Wiki". mywiki.wooledge.org. Retrieved 10 January 2024.
77. "BashGuide/TestsAndConditionals - Greg's Wiki". mywiki.wooledge.org. Retrieved 10 January 2024.
78. "CHANGES - bash.git - bash". git.savannah.gnu.org. Retrieved 10 January 2024.
79. "Bash changes [Bash Hackers Wiki]". 14 February 2021. Archived from the original on 14 February 2021. Retrieved 10 January 2024.
80. "Obsolete and deprecated syntax [Bash Hackers Wiki]". 11 February 2021. Archived from the original on 11 February 2021. Retrieved 10 January 2024.
81. "The Open Group Base Specifications Issue 7, 2018 edition". pubs.opengroup.org.
82. "BASH(1) Manual Page". tiswww.case.edu.
83. "bash.0\doc - bash.git - bash". git.savannah.gnu.org.
84. "The GNU Bourne-Again Shell". tiswww.case.edu.
85. "Frequently Asked Questions".
86. Chazelas, Stephane (4 October 2014). "oss-sec mailing list archives". Seclists.org. Archived from the original on 6 October 2014. Retrieved 4 October 2014.
87. Leyden, John (24 September 2014). "Patch Bash NOW: 'Shell Shock' bug blasts OS X, Linux systems wide open". The Register. Archived from the original on 16 October 2014. Retrieved 25 September 2014.
88. Perlroth, Nicole (25 September 2014). "Security Experts Expect 'Shellshock' Software Bug in Bash to Be Significant". The New York Times. Archived from the original on 5 April 2019. Retrieved 25 September 2014.
89. Seltzer, Larry (29 September 2014). "Shellshock makes Heartbleed look insignificant". ZDNet. Archived from the original on 14 May 2016.
90. GNU Project. "README file". Archived from the original on 26 April 2019. Retrieved 16 April 2014. Bash is free software, distributed under the terms of the [GNU] General Public License as published by the Free Software Foundation, version 3 of the License (or any later version).
91. "bash-1.11". oldlinux.org. Archived from the original on 15 October 2021. Retrieved 9 June 2021. See test.c for GPL-2.0-or-later
92. "bash-1.05.tar". oldlinux.org.
93. "Is there a way to download the presumably initial bash source bash-0.99?". unix.stackexchange.com.
94. "How to install Bash shell command-line tool on Windows 10". 28 September 2016. Archived from the original on 20 November 2016. Retrieved 20 November 2016.
95. Hoffman, Chris (30 July 2021). "How to Install the Windows Subsystem for Linux on Windows 11". How-To Geek. Retrieved 12 October 2022.
96. "User Environment Feature Changes". Oracle. Archived from the original on 12 June 2018. Retrieved 8 June 2018.
97. "github version history NEWS v5.0". GitHub. Archived from the original on 4 May 2022. Retrieved 1 March 2021.
98. "Bash changes [Bash Hackers Wiki]". Archived from the original on 18 March 2020. Retrieved 25 November 2019.
99. "Bash-5.0 release available". lists.gnu.org. Archived from the original on 8 November 2020. Retrieved 1 March 2021.

Further reading

• Stephenson, Neal (2003). In the Beginning... Was the Command Line. HarperCollins. ISBN 978-0380815937.
• "Evolution of shells in Linux". ibm.com. Retrieved 19 May 2024.
• "Scripting Reference :: Scripting with the Bourne-Again Shell (Bash)". berkeley.edu. Retrieved 19 May 2024.
• "IRIS :: Instructional & Research Information Systems :: FAQ: Unix :: About UNIX Shells". berkeley.edu. Retrieved 19 May 2024.