Rc shell

rc is the command line interpreter for Version 10 Unix, Plan 9, and Inferno 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 rewrite of rc for Unix-like operating systems by Byron Rakitzis is also available but includes some incompatible changes. A port of the original rc to Unix is part of Plan 9 from User Space.

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. Rc also supports lists of objects as variables, which eliminates the need for constructs like "$@". For example, the Bourne shell script

if test $1 = hello; then
    echo hello, world
else
    case $2 of
    1) echo $# 'hey' "jude's"$3;;
    2) echo `date` :$*: :"$@":
    *) echo why not 1>&2
    esac
    for i in a b c; do
        # ...
    done
fi

is expressed in rc as

if(~ $1 hello)
    echo hello, world
if not{
    switch($2){
    case 1
        echo $#* 'hey' 'judes'^$3
    case 2
        echo `{date} :$"*: :$*:
    case *
        echo why not >[1=2]
    for(i in a b c){
        # ...
    }
}

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 standard error of a to b — in Bourne shell as a 1>&2 | 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}

External links

• "Rc - The Plan 9 Shell"
• Plan 9 rc manual page
• Plan 9 from User Space - Includes rc and other Plan 9 tools for Linux, OS X and other Unix-like systems.
• Byron Rakitzis' rewrite for Unix

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