Editing Bourne shell (section)

==History==
[[File:Version 7 UNIX SIMH PDP11 Bourne Shell Manual.png|thumb|[[Version 7 Unix]]: the original Bourne shell [[man page|manual page]]. [[PDP-11]] simulation with [[SIMH]]]]

===Origins===

Work on the Bourne shell initially started in 1976.<ref>https://www.bsdcan.org/2015/schedule/events/612.en.html Stephen Bourne Keynote for BSDCan 2015</ref> Developed by [[Stephen R. Bourne|Stephen Bourne]] at [[Bell Labs]], it was a replacement for the [[Thompson shell]], whose executable file had the same name—<code>sh</code>. The Bourne shell was also preceded by the [[PWB shell|Mashey shell]]. Bourne was released in 1979 in the [[Version 7 Unix]] release distributed to colleges and universities. Although it is used as an interactive command interpreter, it was also intended as a [[scripting language]] and contains most of the features that are commonly considered to produce structured programs.

It gained popularity with the publication of ''[[The Unix Programming Environment]]'' by [[Brian Kernighan]] and [[Rob Pike]]—the first commercially published book that presented the shell as a programming language in a tutorial form.{{Citation needed|date=December 2024}}

Some of the primary goals of the shell were:<ref>{{cite web|url=http://www.computerworld.com.au/article/279011/-z_programming_languages_bourne_shell_sh|title=The A-Z of Programming Languages: Bourne shell, or sh|website=computerworld.com.au|access-date=6 March 2009|archive-url=https://web.archive.org/web/20100111203059/http://www.computerworld.com.au/article/279011/-z_programming_languages_bourne_shell_sh|archive-date=11 January 2010|url-status=dead}}</ref>
* To allow [[shell script]]s to be used as [[filter (software)|filters]].
* To provide programmability including [[control flow]] and [[Variable (computer science)|variables]].
* Control over all input/output [[file descriptor]]s.
* Control over [[Unix signal|signal handling]] within scripts.
* No limits on string lengths when interpreting shell scripts.
* Rationalize and generalize string quoting mechanism.
* The [[environment variable|environment mechanism]]. This allowed context to be established at startup and provided a way for shell scripts to pass context to sub scripts ([[Process (computing)|processes]]) without having to use explicit [[parameter (computer science)|positional parameters]].

===Features of the original version===
Features of the Version 7 UNIX Bourne shell include:

* Scripts can be invoked as commands by using their filename
* May be used interactively or non-interactively
* Allows both synchronous and asynchronous execution of commands
* Supports input and output redirection and pipelines
* Provides a set of built-in commands
* Provides flow control constructs and quotation facilities.
* Typeless variables
* Provides local and global variable scope
* Scripts do not require compilation before execution
* Does not have a goto facility, so code restructuring may be necessary
* [[Command substitution]] using [[backquotes]]: <code>`command`</code>.
* [[Here documents]] using <code>&lt;&lt;</code> to embed a block of input text within a script.
* <code>for ~ do ~ done</code> loops, in particular the use of <code>$*</code> to loop over arguments, as well as <code>for ~ in ~ do ~ done</code> loops for iterating over lists.
* <code>case ~ in ~ esac</code> selection mechanism, primarily intended to assist [[argument parsing]].
* <code>sh</code> provided support for environment variables using keyword parameters and exportable variables.
* Contains strong provisions for controlling input and output and in its [[regular expression|expression matching]] facilities.

The Bourne shell also was the first to feature the convention of using [[file descriptor]] <code>2&gt;</code> for [[error message]]s, allowing much greater programmatic control during scripting by keeping error messages separate from data.

Stephen Bourne's coding style was influenced by his experience with the [[ALGOL 68C]] compiler<ref name="reader">{{cite tech report |first1=M. D. |last1=McIlroy |author-link1=Doug McIlroy |year=1987 |url=http://www.cs.dartmouth.edu/~doug/reader.pdf |archive-url=https://web.archive.org/web/20140504225225/http://www.cs.dartmouth.edu/~doug/reader.pdf |archive-date=2014-05-04 |url-status=live |title=A Research Unix reader: annotated excerpts from the Programmer's Manual, 1971–1986 |series=CSTR |number=139 |institution=Bell Labs}}</ref> that he had been working on at [[University of Cambridge|Cambridge University]]. In addition to the style in which the program was written, Bourne reused portions of [[ALGOL 68]]'s <code>'''if''' ~ '''then''' ~ '''elif''' ~ '''then''' ~ '''else''' ~ '''fi'''</code>, <code>'''case''' ~ '''in''' ~ '''esac'''</code> and <code>'''for'''/'''while''' ~ '''do''' ~ '''od'''</code>" (using <code>done</code> instead of <code>'''od'''</code>) clauses in the common [[Unix]] Bourne shell syntax. Moreover, – although the v7 shell is written in [[C (programming language)|C]] – Bourne took advantage of some [[Macro (computer science)|macros]]<ref>{{Cite web| url=http://minnie.tuhs.org/cgi-bin/utree.pl?file=V7/usr/src/cmd/sh/mac.h|title=mac.h – Macros used by Bourne to structure C like Algol68C |access-date=9 September 2006|author=Bourne, Steve|author-link=Stephen R. Bourne|date= 12 January 1979 |publisher=[[AT&T Corporation]] }}</ref> to give the C [[source code]] an ALGOL 68 flavor. These macros (along with the [[Finger protocol|finger]] command distributed in Unix version [[Berkeley Software Distribution#4.2BSD|4.2BSD]]) inspired the [[International Obfuscated C Code Contest]] (IOCCC).<ref>{{Cite web|url=http://www.ioccc.org/faq.html|title=The IOCCC FAQ – Q/A: How did the IOCCC get started?| access-date=9 September 2006|author=Landon Curt Noll|author-link=Landon Curt Noll|author2=Simon Cooper|author3=Peter Seebach|author4=Leonid A. Broukhis|name-list-style=amp|year= 2004|publisher=ioccc.org}}</ref>

===Features introduced after 1979===
Over the years, the Bourne shell was enhanced at AT&T. The various variants are thus called like the respective AT&T Unix version it was released with (some important variants being Version7, System III, SVR2, SVR3, SVR4). As the shell was never versioned, the only way to identify it was testing its features.<ref>{{cite web|url=http://www.in-ulm.de/~mascheck/various/whatshell/|title=what shell is this|website=www.in-ulm.de}}</ref>

Features of the Bourne shell versions since 1979 include:<ref>{{cite web|url=http://www.in-ulm.de/~mascheck/bourne/|title=traditional Bourne shell family / history and development|website=www.in-ulm.de}}</ref>

* Built-in {{code|test}} command – System III shell (1981)
* # as comment character – System III shell (1981)
* Colon in parameter substitutions "${parameter:=word}" – System III shell (1981)
* {{code|continue}} with argument – System III shell (1981)
* {{code|cat <<-EOF}} for indented here documents – System III shell (1981)
* Functions and the {{code|return}} builtin – SVR2 shell (1984)
* Built-ins {{code|unset}}, {{code|echo}}, {{code|type}} – SVR2 shell (1984)
* Source code de-ALGOL68-ized – SVR2 shell (1984)
* Modern "{{code|$@}}" – SVR3 shell (1986)
* Built-in {{code|getopts}} – SVR3 shell (1986)
* Cleaned up parameter handling allows recursively callable functions – SVR3 shell (1986)
* 8-bit clean – SVR3 shell (1986)
* Job control – SVR4 shell (1989)
* Multi-byte support – SVR4 shell (1989)