Red Hat Enterprise Linux 5 Administration Unleashed

240CHAPTER 11Automating Tasks with ScriptsCAUTIONWhen writing a Bash script, use a text editor such as Vi, Emacs, or gEdit (selectAccessories, Text Editor from the Applications menu). Using a more complex wordprocessing application such as OpenOffice.org Writer is not recommended because itautomatically wraps lines or tries to correct capitalization and spelling of words. Becausespacing and end-of-line characters are used in Bash to form structures such as loops,the built-in formatting of a word processor can cause syntax errors in Bash scripts.All Bash scripts must start with a line that defines it as a Bash script:#!/bin/bashAny other lines that begin with the hash mark (#) are considered comments and are notprocessed as lines of code. For example, you can add a small description of what the programdoes, the author, when it was last modified, and a version number to the top of the script:#!/bin/bash# This program creates daily backups for Company Name# For internal use only# Author: Your Name Here# Last modified: May 15, 2006# Version: 1.5TIPFor a complete Bash reference, refer to the “Bash Reference Manual” athttp://www.gnu.org/software/bash/manual/.Executing Commands in a Bash ScriptTo execute a series of commands in a Bash script, list each command on a separate line.For example, Listing 11.1 shows the very basic Bash script that gathers information aboutsystem resources.LISTING 11.1 Generating a System Resources Report, Version 1#!/bin/bash#Script to generate a system resources report#Author: Tammy Foxuptimempstatsarfree -mdf -hvmstat -d