Command Interpreters and Command Pipelines

This section provides a quick introduction of UNIX command interpreters, shells, and command pipelines.

Unix supports command interpreters as separate programs called shells. Multiple shells can be supported on a single UNIX system. The following commands session shows 4 shells are supported on the system. User can switch shells at any time:

$ls /bin | grep sh
   bash 
   csh  
   sh   
   tcsh 

   (Listing all available shells

$set | grep -i shell
SHELL=/bin/sh

   (Looking at the current shell

$tcsh
%

   (Switching to Tcsh   

%set | grep -i shell
shell   /bin/tcsh

   (Looking at the current shell

%exit
$

   Switching back to the first shell

Unix supports command pipelines so that multiple commands can be linked with data producer-consumer relations. The following commands session shows some examples of command pipelines:

%tar -cO * | compress > backup.tar.Z
   (Combining all files into an archive and compress it to a file

%who | pr -2 | lpr -Pxx
   (Printing all logged in users in 2 columns

%curl "http://en.wikipedia.org/wiki/Pipeline (Unix)" | \
   sed 's/[^a-zA-Z ]/ /g' | \
   tr 'A-Z ' 'a-z\n' | \
   grep '[a-z]' | \
   sort -u | \
   comm -23 - /usr/dict/words
   
   (Spell-checking a Web page source code

Table of Contents

 About This Book

 1957 - FORTRAN Language Developed by IBM

1970 - UNIX Operating System Developed by AT&T Bell Labs

 What Is UNIX?

Command Interpreters and Command Pipelines

 UNIX File System Hierarchy

 1971 - FTP Protocol Created by Abhay Bhushan

 1972 - C Language Developed by Dennis Ritchie

 1976 - vi Text Editor Developed by Bill Joy

 1977 - Apple II Designed by Steve Jobs and Steve Wozniak

 1977 - The Bourne Shell Developed by Stephen Bourne

 1978 - The C Shell Developed by Bill Joy

 1978 - Bash (Bourne-Again Shell) Developed by Brian Fox

 1979 - The Tcsh (TENEX C Shell) Developed by Ken Greer

 1983 - "Sendmail" Mail Transfer Agent Developed by Eric Allman

 1984 - Macintosh Developed by Apple Inc.

 1984 - X Window System Developed a MIT Team

 1991 - WWW (World Wide Web) Developed by Tim Berners-Lee

 1991 - Gopher Protocol Created by a University of Minnesota Team

 1995 - Java Language Developed by Sun Microsystems

 1995 - PHP: Hypertext Preprocessor Created by Rasmus Lerdorf

 2002 - .NET Framework Developed by Microsoft

 References

 PDF Printing Version