Editing Unix shell (section)

==Early shells==
The first Unix shell was the [[Thompson shell]], ''sh'', written by [[Ken Thompson (computer programmer)|Ken Thompson]] at [[Bell Labs]] and distributed with Versions 1 through 6 of Unix, from 1971 to 1975.<ref name="v6hist">{{ cite web|url=http://v6shell.org/history/ |title=V6 Thompson Shell Port - History |publisher=V6shell.org |access-date=2012-08-14 }}</ref> Though rudimentary by modern standards, it introduced many of the basic features common to all later Unix shells, including piping, simple control structures using <code>if</code> and <code>goto</code>, and filename wildcarding.  Though not in current use, it is still available as part of some [[Ancient UNIX]] systems.

It was modeled after the [[Multics]] shell, developed in 1965 by American software engineer [[Glenda Schroeder]]. Schroeder's Multics shell was itself modeled after the [[RUNCOM]] program [[Louis Pouzin]] showed to the Multics Team. The "rc" suffix on some Unix configuration files (e.g.  ".bashrc" or ".vimrc"), is a remnant of the RUNCOM ancestry of Unix shells.<ref name="Vleck">{{ cite web|author=Tom Van Vleck |url=http://www.multicians.org/unix.html |title=Unix and Multics |publisher=Multicians.org |date=1995-02-05 |access-date=2012-08-14 }}</ref><ref name="Pouzin">{{ cite web|author=Louis Pouzin |url=http://www.multicians.org/shell.html |title=The Origin of the Shell |publisher=Multicians.org |date=2000-11-25 |access-date=2012-08-14 }}</ref>

The [[PWB shell]] or Mashey shell, ''sh'', was an upward-compatible version of the Thompson shell, augmented by [[John Mashey]] and others and distributed with the [[PWB/UNIX|Programmer's Workbench UNIX]], circa 1975–1977. It focused on making shell programming practical, especially in large shared computing centers. It added shell variables (precursors of [[environment variable]]s, including the search path mechanism that evolved into $PATH), user-executable shell scripts, and interrupt-handling.  Control structures were extended from if/goto to if/then/else/endif, switch/breaksw/endsw, and while/end/break/continue.  As shell programming became widespread, these external commands were incorporated into the shell itself for performance.

But the most widely distributed and influential of the early Unix shells were the [[Bourne shell]] and the [[C shell]]. Both shells have been used as the coding base and model for many derivative and work-alike shells with extended feature sets.<ref>{{cite web|url=http://www.softpanorama.org/People/Shell_giants/introduction.shtml|title=Introduction to the Unix shell history|author=Nikolai Bezroukov|author-link=Nikolai Bezroukov|publisher=Softpanorama|date=2015-08-13|access-date=2016-08-21|archive-url=https://web.archive.org/web/20220608181527/http://www.softpanorama.org/People/Shell_giants/introduction.shtml|archive-date=2022-06-08|url-status=dead}}</ref>

===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|$}}).

===C shell===
The [[C shell]], ''csh'', was modeled on the C programming language, including the control structures and the expression grammar. It was written by [[Bill Joy]] as a graduate student at [[University of California, Berkeley]], and was widely distributed with [[Berkeley Software Distribution|BSD Unix]].<ref>Harley Hahn, [https://www.harley.com/unix-book/book/chapters/h.html Harley Hahn's Guide to Unix and Linux: Unix/Linux Timeline].</ref>{{better source|date=September 2023}}

The C shell also introduced many features for interactive work, including the [[C shell#History|history]] and [[C shell#Editing operators|editing]] mechanisms, [[C shell#Aliases|aliases]], [[C shell#Directory stack|directory stacks]], [[C shell#Tilde notation|tilde notation]], [[C shell#Cdpath|cdpath]], [[C shell#Job control|job control]] and [[C shell#Path hashing|path hashing]].  On many systems, csh may be a [[symbolic link]] or [[hard link]] to [[TENEX C shell]] (tcsh), an improved version of Joy's original version.  Although the interactive features of csh have been copied to most other shells, the language structure has not been widely copied.  The only work-alike is [[Hamilton C shell]], written by Nicole Hamilton, first distributed on [[OS/2]] in 1988 and on [[Windows]] since 1992.<ref>{{cite web|url=http://hamiltonlabs.com/ReleaseNotes.htm|title=Hamilton C shell for Windows Release Notes 4.0|access-date=20 September 2014}}</ref>