rc

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").[1]

This article is about the shell. For other uses, see RC (disambiguation).
rc
Paradigmimperative, pipeline
Designed byTom Duff
DeveloperBell Labs
First appeared1989 (1989)
Typing disciplineweak
OSCross-platform (Version 10 Unix, Plan 9, Plan 9 from User Space)
Websitedoc.cat-v.org/plan_9/4th_edition/papers/rc
Dialects
Byron's rc
Influenced by
Bourne shell
Influenced
es, The Inferno shell.
An rc session

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.[1]

Influences

es

es (for "extensible shell") is an open source, command line interpreter developed by Rakitzis and Paul Haahr[2] that uses a scripting language syntax influenced by the rc shell.[3][4] It was originally based on code from Byron Rakitzis's clone of rc for Unix.[5][6]

Extensible shell is intended to provide a fully functional programming language as a Unix shell.[7] 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,[8] Official releases appear to have ceased after 0.9-beta-1 in 1997,[9] and es lacks features as compared to more popular shells, such as zsh and bash.[10] A public domain fork of es is active as of 2019.[11]

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[1]: 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"[1]: Pipeline Branching 

References
  1. Duff, Tom. Rc — The Plan 9 Shell. {{cite book}}: |work= ignored (help) (PDF; 1990 version)
  2. Fischer, Manfred M. (13 December 1996). Spatial Analytical Perspectives on GIS. CRC Press. ISBN 9780748403400.
  3. "Ubuntu Manpage: es - extensible shell". Manpages.ubuntu.com. 1992-03-05. Archived from the original on 2014-02-24. Retrieved 2012-08-24.
  4. "Extensible Shell". FOLDOC. Retrieved 2012-08-24.
  5. "Shells Available for Linux". LUV. Retrieved 2012-08-24.
  6. Jones, Tim. "Evolution of shells in Linux". IBM. Retrieved 14 March 2014.
  7. "Linux Journal 12: What's GNU". Archived from the original on 2013-01-17. Retrieved 2012-08-24.
  8. Es: A shell with higher-order functions by Byron Rakitzis, NetApp, Inc, and Paul Haahr, Adobe Systems Incorporated; Archived at Archive.Org.
  10. "UNIX shell differences". Faqs.org. Retrieved 2012-08-24.
  11. Haggerty, James (13 March 2020). "wryun/es-shell: a shell with higher-order functions". GitHub.
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