Paradigm(s) | imperative, pipeline |
---|---|
Appeared in | 1989 |
Designed by | Tom Duff |
Developer | Bell Labs |
Typing discipline | weak |
Dialects | Byron's rc |
Influenced by | Bourne shell |
Influenced | Es shell, The Inferno shell. |
OS | Cross-platform (Version 10 Unix, Plan 9, Plan 9 from User Space) |
Website | Rc - The Plan 9 Shell |
rc 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 called Duff's device.
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 ALGOL-like, as the original Bourne shell uses, except that it uses a construct if not 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 "$@".
For example, the Bourne shell script
if test "$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 }
Because if and if not 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 of a to b — in Bourne shell as a 3>&2 2>&1 >&3 | b a <>b # opens b as a's standard input and standard output a <{b} <{c} # becomes a {standard output of b} {standard output of c}
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