Rc (Unix shell): Difference between revisions

Revision as of 21:23, 7 February 2020

Revision as of 08:32, 31 March 2020

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| 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 book |last1=Duff |first1=Tom |title=Rc — The Plan 9 Shell |url=http://doc.cat-v.org/plan_9/4th_edition/papers/rc}} ([https://www.scs.stanford.edu/nyu/04fa/sched/readings/rc.pdf PDF])</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 structures, 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>". The syntax is described in Duff's paper.<ref name=RCTD/>

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

===es===

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Because <code>if</code> and <code>if not</code> are two different statements, they must be grouped in order to be used in certain situations.{{clarification needed |date=January 2019}}

Rc also supports more dynamic piping:

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

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

a <{>b} <{c} ''# becomesopens file b as a's {[[standard outputinput]] ofand b} {[[standard output of c}]]''{{clarification needed |date=January 2019}}

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==