rc

From Wikipedia, the free encyclopedia
  (Redirected from Es (Unix shell))
Jump to: navigation, search
This article is about the shell. For other uses, see RC (disambiguation).
rc
Paradigm imperative, pipeline
Designed by Tom Duff
Developer Bell Labs
First appeared 1989; 26 years ago (1989)
weak
OS Cross-platform (Version 10 Unix, Plan 9, Plan 9 from User Space)
Website Rc - The Plan 9 Shell
An rc session

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 ("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 "$@".

Influences[edit]

es[edit]

es (for "extensible shell") is an Open source, command line interpreter developed by Rakitzis and Paul Haahr,[1] that uses a scripting language syntactically similar to the rc shell.[2][3] It was originally based on code from Byron Rakitzis's clone of rc for Unix[4][5]

Extensible shell is intended to provide a fully functional programming language as a Unix shell.[6] The bulk of es development occurred in the early 1990s, after the shell was introduced at the Winter 1993 USENIX conference in San Diego,[7] Official releases appear to have ceased after 0.9-beta-1 in 1997,[8] and standard es lacks features as compared to more popular shells, such as zsh and bash.[9]

Examples[edit]

For example, 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
}

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}

References[edit]

  1. ^ Spatial Analytical Perspectives on GIS. 
  2. ^ "Ubuntu Manpage: es - extensible shell". Manpages.ubuntu.com. 1992-03-05. Retrieved 2012-08-24. 
  3. ^ "Extensible Shell". FOLDOC. Retrieved 2012-08-24. 
  4. ^ "Shells Available for Linux". LUV. Retrieved 2012-08-24. 
  5. ^ Jones, Tim. "Evolution of shells in Linux". IBM. Retrieved 14 March 2014. 
  6. ^ "Linux Journal 12: What's GNU". Retrieved 2012-08-24. 
  7. ^ Es: A shell with higher-order functions by Byron Rakitzis, NetApp, Inc, and Paul Haahr, Adobe Systems Incorporated; Archived at Archive.Org.
  8. ^ [1]
  9. ^ "UNIX shell differences". Faqs.org. Retrieved 2012-08-24. 

External links[edit]