Linux System Administration

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Chapter 10: Scripting

bash Beginnings

Many operating systems offered command-line interfaces in the early days, and they

typically allowed commands to be stored in text files and run as batch jobs (a readily

understood concept at the time). It soon became natural to introduce ways to sub-

mit parameters to scripts and allow the scripts to change their behavior under differ-

ent conditions. Unix’s shell made tremendous leaps in flexibility, turning the shell

into a true programming language.

Our interactive examples will show a sample shell prompt,acommand with optional

arguments, and the command’s output, like this:

admin@server1:~$ date

Thu Aug 24 09:16:56 CDT 2006

We’ll show the contents of a shell script like this:

#!/bin/bash

contents of script...

The first line is special in Linux scripts: if it starts with the two characters #!, the rest

of the first line is the filename of the command to run to process the rest of the

script. (If the

# character is not followed by a !, it’s interpreted as a comment that

continues until the end of the line.) This trick lets you use any program to interpret

your script files. If the program is a traditional shell like sh or bash, the file is called a

shell script. At the end of the chapter we’ll show scripts for Perl, PHP, and Python.

Microsoft Windows uses the suffix of the filename to define the file

type and what interpreter should run it. If you change ...