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Chapter 6. The Linux Shells: An Overview
The shell is a program that acts as a buffer between you and the
operating system. In its role as a command interpreter, it should
(for the most part) act invisibly. It also can be used for simple
programming.
This section introduces three shells commonly used on Linux
systems -- the Bourne-Again shell (bash), the C shell (csh), and
csh's
enhanced version, tcsh -- and summarizes the major differences
between them. Details on them are provided in Chapter 7, "bash: The Bourne-Again Shell", and Chapter 8, "csh and tcsh". (Some Linux distributions also offer the
Korn shell, ksh, another popular version of the Bourne shell with
some of the same features as bash.)
The following topics are presented in this chapter:
Purpose of the shell Shell flavors Common features Differing features
6.1. Purpose of the Shell
There are three main uses for the shell:
6.1.1. Interactive Use
When the shell is used interactively, it waits for you to issue
commands, processes them (to interpret special characters,
such as wildcards), and executes them. Shells also provide a set of
commands, known as built-ins, to supplement Linux
commands.
6.1.2. Customization of Your Linux Session
A Linux shell defines variables, such as the locations of your home
directory and mail spool, to control the behavior of your session.
Some variables are preset by the system; you can define others
in startup files that your shell reads when you log in. Startup
files also can contain Linux or shell commands, for execution immediately after login.
6.1.3. Programming
A series of individual commands (be they shell or other Linux commands
available on the system)
combined into one executable file is called a shell script. Batch files in
MS-DOS are a similar concept. bash is considered a powerful programming
shell, while scripting in csh is rumored to be hazardous to your health.
 |  |  | | 5.2. The Debian Package Manager |  | 6.2. Shell Flavors |
Copyright © 2001 O'Reilly & Associates. All rights reserved.
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