rc (Unix shell)
{{short description|Command line interpreter for Version 10 Unix and Plan 9 from Bell Labs operating systems}}
{{lowercase|title=rc}}
{{refimprove|date=March 2014}}
{{Infobox programming language
| name = rc
| logo =
| paradigm = imperative, pipeline
| year = {{Start date and age|1989}}
| designer = Tom Duff
| developer = Bell Labs
| latest_release_version =
| latest_release_date =
| latest_test_version =
| latest_test_date =
| source_model = Open source
| typing = weak
| implementations =
| dialects = Byron's rc
| influenced_by = Bourne shell
| influenced = es, the Inferno shell
| operating_system = Cross-platform (Version 10 Unix, Plan 9, Plan 9 from User Space)
| license =
| website =
}}
File:Plan 9 from Bell Labs (process management).png
rc (for "run commands") is the command line interpreter for Version 10 Unix and Plan 9 from Bell Labs operating systems. 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 construct ("Duff's device").{{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}}
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 if not construct instead of else, and has a Bourne-like for loop to iterate over lists. In rc, all variables are lists of strings, which eliminates the need for constructs like "$@". Variables are not re-split when expanded. The language is described in Duff's paper.
==Influences==
=es=
es (for "extensible shell") is an open source, command line interpreter developed by Rakitzis and Paul Haahr{{cite book | url=https://books.google.com/books?id=iEK6eQQwOF0C&pg=PA43 | title=Spatial Analytical Perspectives on GIS| isbn=9780748403400| last1=Fischer| first1=Manfred M.| date=13 December 1996| publisher=CRC Press}} that uses a scripting language syntax influenced by the rc shell.{{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 |access-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 }}{{cite web | url=http://foldoc.org/Extensible+Shell |title=Extensible Shell |publisher=FOLDOC |access-date=2012-08-24}} It was originally based on code from Byron Rakitzis's clone of rc for Unix.{{cite web | url=http://luv.asn.au/overheads/shells-talk.html |title=Shells Available for Linux |publisher=LUV |access-date=2012-08-24}}{{cite web|last=Jones|first=Tim|title=Evolution of shells in Linux|url=http://www.ibm.com/developerworks/library/l-linux-shells/|publisher=IBM|access-date=14 March 2014}}
Extensible shell is intended to provide a fully functional programming language as a Unix shell.{{cite web|url=http://nnc3.com/lj/LJ/LJ12/0062.html|title=Linux Journal 12: What's GNU|access-date=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}} It does so by introducing "program fragments" in braces as a new datatype, lexical scoping via 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.[http://stuff.mit.edu/afs/sipb/user/yandros/doc/es-usenix-winter93.html Es: A shell with higher-order functions] by Byron Rakitzis, NetApp, Inc, and Paul Haahr, Adobe Systems Incorporated; Archived at [https://web.archive.org/web/20090415213858/http://192.220.96.201/es/es-usenix-winter93.html Archive.Org]. Official releases appear to have ceased after 0.9-beta-1 in 1997,[ftp://ftp.sys.utoronto.ca/pub/es/] and es lacks features present in more popular shells, such as zsh and bash.{{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}} A public domain fork of {{code|es}} is active {{as of|2019|lc=yes}}.{{cite web |last1=Haggerty |first1=James |title=wryun/es-shell: a shell with higher-order functions |url=http://wryun.github.io/es-shell/ |website=GitHub |date=13 March 2020}}
Examples
The Bourne shell script:
if [ "$1" = "hello" ]; then
echo hello, world
else
case "$2" in
1) echo $# 'hey' "jude's"$3;;
2) echo `date` :$*: :"$@":;;
*) echo why not 1>&2
esac
for i in a b c; do
echo $i
done
fi
is expressed in rc as:
if(~ $1 hello)
echo hello, world
if not {
switch($2) {
case 1
echo $#* 'hey' 'jude''s'^$3
case 2
echo `{date} :$"*: :$*:
case *
echo why not >[1=2]
}
for(i in a b c)
echo $i
}
Rc also supports more dynamic piping:
a |[2] b # pipe only standard error of a to b — equivalent to '3>&2 2>&1 >&3 | b' in Bourne shell{{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"{{rp|at=Pipeline Branching}}
References
{{reflist|25em}}
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
- [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]
{{Unix Shells}}
Category:Inferno (operating system)
Category:Plan 9 from Bell Labs
Category:Procedural programming languages
Category:Programming languages created in 1989