Editing Unix shell (section)

===Bourne shell===
The [[Bourne shell]], ''sh'', was a new Unix shell by [[Stephen R. Bourne|Stephen Bourne]] at Bell Labs.<ref>{{cite interview|url=https://www2.computerworld.com.au/article/279011/a-z_programming_languages_bourne_shell_sh/|title=The A-Z of Programming Languages: Bourne shell, or sh|first=Stephen|last=Bourne|subject-link=Stephen R. Bourne|interviewer=Howard Dahdah|date=2009-03-05|publisher=[[Computerworld]]|access-date=2022-08-16}}</ref> Distributed as the shell for UNIX Version 7 in 1979, it introduced the rest of the basic features considered common to all the later Unix shells, including [[here document]]s, [[command substitution]], more generic [[Variable (programming)|variables]] and more extensive builtin [[control flow|control structures]].  The language, including the use of a reversed keyword to mark the end of a block, was influenced by [[ALGOL 68]].<ref>{{cite web|url=http://groups.google.com/group/comp.lang.misc/msg/d58db4799c33e093?hl=en&dmode=source|title=''Re: Late Bloomers Revisited''|access-date=20 September 2014}}</ref>  Traditionally, the Bourne shell program name is {{mono|sh}} and its path in the Unix file system hierarchy is {{mono|/bin/sh}}.  But a number of compatible work-alikes are also available with various improvements and additional features.  On many systems, sh may be a [[symbolic link]] or [[hard link]] to one of these alternatives:

* [[Almquist shell]] (ash): written as a BSD-licensed replacement for the Bourne Shell; often used in resource-constrained environments. The sh of [[FreeBSD]], [[NetBSD]] (and their derivatives) are based on ash that has been enhanced to be [[POSIX]] conformant.
** [[Busybox]]: a set of Unix utilities for small and embedded systems, which includes 2 shells: ash, a derivative of the Almquist shell; and hush, an independent implementation of a Bourne shell.
** [[Debian Almquist shell]] (dash): a modern replacement for ash in [[Debian]] and [[Ubuntu (operating system)|Ubuntu]]
* [[Bash (Unix shell)|Bourne-Again shell]] (bash): written as part of the [[GNU Project]] to provide a superset of Bourne Shell functionality. This shell can be found installed and is the default interactive shell for users on most [[Linux]] systems; it provides both interactive mode (implemented by GNU Readline) or script-mode.
* [[KornShell]] (ksh): written by [[David Korn (computer scientist)|David Korn]] based on the Bourne shell sources<ref>
{{citation
| title = ksh - An Extensible High Level Language
| last = Korn
| first = David G.
| publisher = USENIX Association
| journal = Proceedings of the USENIX 1994 Very High Level Languages Symposium
| date = October 26, 1994
| url = https://www.usenix.org/legacy/publications/library/proceedings/vhll/full_papers/korn.ksh.a
| quote = Instead of inventing a new script language, we built a form entry system by modifying the Bourne shell, adding built-in commands as necessary.
| access-date = February 5, 2015
}}</ref> while working at [[Bell Labs]]
* [[pdksh|Public domain Korn shell]] (pdksh)
** [[mksh|MirBSD Korn shell]] (mksh): a descendant of the [[OpenBSD]] /bin/ksh and pdksh, developed as part of [[MirOS BSD]]
* [[Z shell]] (zsh): a relatively modern shell that is partially [[backward compatible]] with [[bash (Unix shell)|bash]]. It's the default shell in [[Kali Linux]] since 2020.4 and [[macOS]] since 10.15 [[macOS Catalina|Catalina]].

The [[POSIX]] standard specifies its standard shell as a strict subset of the [[KornShell|Korn shell]], an enhanced version of the Bourne shell. From a user's perspective the Bourne shell was immediately recognized when active by its characteristic default command line prompt character, the dollar sign ({{mono|$}}).