Rc (Unix shell): Difference between revisions

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{{short description|Command line interpreter for Version 10 Unix and Plan 9 from Bell Labs operating systems}}

{{about|the shell||RC (disambiguation)}}

{{lowercase|title=rc}}

{{refimprove|date=March 2014}}

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| latest_test_version =

| latest_test_date =

| source_model = [[Open source]]

| typing = [[weak typing|weak]]

| implementations =

| dialects = Byron's rc

| influenced_by = [[Bourne shell]]

| influenced = [[#es (Unix shell)|es]], Thethe [[Inferno (operating system)|Inferno]] shell.

| operating_system = [[Cross-platform]] ([[Version 10 Unix]], [[Plan 9 from Bell Labs|Plan 9]], [[Plan 9 from User Space]])

| license =

| website = [http://doc.cat-v.org/plan_9/4th_edition/papers/rc Rc - The Plan 9 Shell]

}}

[[File:Plan 9 from Bell Labs (process management).png|thumb|An rc session]]

'''rc''' (for "[[run commands]]") is the [[command -line interpreter]] for [[Version 10 Unix]] and [[Plan 9 from Bell Labs]] [[operating system]]s. It resembles the [[Bourne shell]], but its syntax is somewhat simpler. It was created by [[Tom Duff]], who is better known for an unusual [[C (programming language)|C programming language]] construct ("[[Duff's device]]").<ref name="RCTD">{{Cite web |last=Duff |first=Tom |date=1990 |title="Rc — The Plan 9 Shell" |url=http://doc.cat-v.org/plan_9/4th_edition/papers/rc |access-date=2024-01-26 |website=cat-v}}</ref>

A port of the original rc to Unix is part of [[Plan 9 from User Space]]. A rewrite of rc for [[Unix-like]] operating systems by Byron Rakitzis is also available but includes some incompatible changes.

Rc uses C-like control structures instead of the original Bourne shell's [[ALGOL]]-like, as the original Bourne shellstructures, except that it uses an <code>if not</code> construct instead of <code>else</code>, and has a Bourne-like <code>for</code> loop to iterate over lists. In rc, all variables are lists of strings, which eliminates the need for constructs like "<code>[[$@|"$@"]]</code>". Variables are not re-split when expanded. The language is described in Duff's paper.<ref name=RCTD/>

==Influences== <!--Anchor from redirected [es[Es (Unix shell)]] article; caution with changes. -->

===es===

''es'' (for "extensible shell") is an [[Openopen source]], [[command line interpreter]] developed by Rakitzis and Paul Haahr,<ref>{{cite book | url=https://books.google.com/books?id=iEK6eQQwOF0C&pg=PA43&redir_esc=y#v=onepage&q&f=false | title=Spatial Analytical Perspectives on GIS| isbn=9780748403400| last1=Fischer| first1=Manfred M.| date=13 December 1996| publisher=CRC Press}}</ref> that uses a [[scripting language]] syntacticallysyntax similarinfluenced toby the rc shell.<ref>{{cite web | url=http://manpages.ubuntu.com/manpages/hardy/man1/es.1.html |title=Ubuntu Manpage: es - extensible shell |publisher=Manpages.ubuntu.com |date=1992-03-05 |accessdateaccess-date=2012-08-24 |url-status=dead |archive-url=https://web.archive.org/web/20140224211945/http://manpages.ubuntu.com/manpages/hardy/man1/es.1.html |archive-date=2014-02-24 }}</ref><ref>{{cite web | url=http://foldoc.org/Extensible+Shell |title=Extensible Shell |publisher=FOLDOC |access-date= |accessdate=2012-08-24}}</ref> It was originally based on code from Byron Rakitzis's clone of [[rc shell|rc]] for Unix.<ref>{{cite web | url=http://luv.asn.au/overheads/shells-talk.html |title=Shells Available for Linux |publisher=LUV |access-date=2012-08-24 |accessdatearchive-date=2012-0803-2422 |archive-url=https://web.archive.org/web/20120322025924/http://luv.asn.au/overheads/shells-talk.html |url-status=dead }}</ref><ref>{{cite web|last=Jones|first=Tim|title=Evolution of shells in Linux|url=http://www.ibm.com/developerworks/library/l-linux-shells/|publisher=IBM|accessdateaccess-date=14 March 2014}}</ref>

Extensible shell is intended to provide a fully [[functional programming|functional]] [[programming language]] as a [[Unix shell]].<ref>{{cite web | url=http://nnc3.com/lj/LJ/LJ12/0062.html |title=Linux Journal 12: What's GNU |access-date= |accessdate=2012-08-24|url-status=dead|archive-url=https://web.archive.org/web/20130117064248/http://nnc3.com/lj/LJ/LJ12/0062.html|archive-date=2013-01-17}}</ref> It does so by introducing "program fragments" in braces as a new datatype, lexical scoping via [[Let expression|let]], and some more minor improvements. The bulk of es development occurred in the early 1990s, after the shell was introduced at the Winter 1993 [[USENIX]] conference in [[San Diego]],.<ref>[http://stuff.mit.edu/afs/sipb/user/yandros/doc/es-usenix-winter93.html Es: A shell with higher-order functions] by Byron Rakitzis, [[NetApp|NetApp, Inc]], and Paul Haahr, [[Adobe Systems Incorporated]]; <u>Archived</u> at [httphttps://web.archive.org/web/20090415213858/http://192.220.96.201/es/es-usenix-winter93.html Archive.Org].</ref> Official releases appear to have ceased after 0.9-beta-1 in 1997,<ref>[https://web.archive.org/web/20230308211038/ftp://ftp.sys.utoronto.ca/pub/es/ ]</ref> and standard es lacks features aspresent compared toin more popular shells, such as [[zsh]] and [[Bash (Unix shell)|bash]].<ref>{{cite web | url=http://www.faqs.org/faqs/unix-faq/shell/shell-differences/ |title=UNIX shell differences| publisher=Faqs.org | access-date=2012-08-24}}</ref> A [[public ___domain]] fork of {{code|es}} accessdateis active {{as of|2019|lc=2012yes}}.<ref>{{cite web |last1=Haggerty |first1=James |title=wryun/es-08shell: a shell with higher-24order functions |url=http://wryun.github.io/es-shell/ |website=GitHub |date=13 March 2020}}</ref>

==Examples==

For example, theThe Bourne shell script:

<sourcesyntaxhighlight lang="bash">

if [ "$1" = "hello" ]; then

echo hello, world

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done

fi

</syntaxhighlight>

</source>

is expressed in rc as:

<sourcesyntaxhighlight lang="text">

if(~ $1 hello)

echo hello, world

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echo $i

}

</syntaxhighlight>

</source>

Because <tt>if</tt> and <tt>if not</tt> are two different statements, they must be grouped in order to be used in certain situations.

Rc also supports more dynamic piping:

a |[2] b ''# pipe only [[standard error stream|standard error]] of a to b — inequivalent [[Bourne shell]] as ato '3>&2 2>&1 >&3 | b' in [[Bourne shell]]''<ref name=RCTD/>{{rp|at=Advanced I/O Redirection}}

a <>b ''# opens file b as a's [[standard input]] and [[standard output]]''

a <{b} <{c} ''# becomes a {standard output of b} {standard output of c},''

# ''better known as "[[process substitution]]"''<ref name=RCTD/>{{rp|at=Pipeline Branching}}

==References==

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==External links==

*{{man|1|rc|Plan 9||inline}} - Plan 9 manual page.

*[https://9fans.github.io/plan9port/ Plan 9 from User Space] - Includes rc and other Plan 9 tools for Linux, Mac OS X and other Unix-like systems

*[http://tobold.org/article/rc Byron Rakitzis' rewrite for Unix]

*[https://github.com/rakitzis/rc Byron Rakitzis' rewrite for Unix] ([http://tobold.org/article/rc article] {{Webarchive|url=https://web.archive.org/web/20131005004955/http://tobold.org/article/rc |date=2013-10-05 }})

*[http://hawkwind.utcs.utoronto.ca:8001/mlists/es.html es Official website]