thumb|An rc session
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").
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> in the original implementation but uses <code>else</code> in Byron Rakitzis' implementation, 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. that uses a scripting language syntax influenced by the rc shell. It was originally based on code from Byron Rakitzis's clone of rc for Unix.
Extensible shell is intended to provide a fully functional programming language as a Unix shell. 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. Official releases appear to have ceased after 0.9-beta-1 in 1997, and es lacks features present in more popular shells, such as zsh and bash. A public domain fork of is active .
Examples
The Bourne shell script:
<syntaxhighlight lang="bash">
if [ hello = "$1" ]; 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
</syntaxhighlight>
is expressed in rc as:
<syntaxhighlight lang="text">
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)
echo $i
}
</syntaxhighlight>
Rc also supports more dynamic piping:
a |[2] b # pipe only standard error of a to b — equivalent to '{ a 2>&1 >&3 3>&- | b; } 3>&1' in Bourne shell