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

   (Listing all available shells

$set | grep -i shell

   (Looking at the current shell


   (Switching to Tcsh

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

   (Looking at the current shell


   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 " (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

 2002 - .NET Framework Developed by Microsoft

 1995 - PHP: Hypertext Preprocessor Created by Rasmus Lerdorf

 1995 - Java Language Developed by Sun Microsystems

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

 1991 - Gopher Protocol Created by a University of Minnesota Team

 1984 - X Window System Developed a MIT Team

 1984 - Macintosh Developed by Apple Inc.

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

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

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

 1978 - The C Shell Developed by Bill Joy

 1977 - The Bourne Shell Developed by Stephen Bourne

 1977 - Apple II Designed by Steve Jobs and Steve Wozniak

 1976 - vi Text Editor Developed by Bill Joy

 1974 - Internet by Vinton Cerf

 1972 - C Language Developed by Dennis Ritchie

 1971 - FTP Protocol Created by Abhay Bhushan

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

 What Is UNIX

Command Interpreters and Command Pipelines

 UNIX File System Hierarchy

 1957 - FORTRAN Language Developed by IBM


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