Secrets in This Chapter
Looking at Some Shell Scripts
Learning the Basics of Shell Scripting in Bash
Using Bash Control Structures
Perl as a Scripting Language
Writing Your First Perl Script
Using Variables in Perl
Using Operators and Expressions
Learning Regular Expressions
Using if and unless Statements
Using the while Statement
Using for and foreach Statements
Using the goto Statement
Working with Files
Writing Perl Subroutines
Using a Perl Module
Using Perl Objects
The fundamental philosophy of UNIX, which Linux continues to follow, is to give the user many small and specialized commands, along with the plumbing necessary to connect these commands. By plumbing, I mean the way in which one command's output functions as a second command's input. Bash, the default shell in Linux, provides this plumbing in the form of I/O redirection and pipes. Bash also includes features such as the if statement, which runs commands only when a specific condition is true, and the for statement, which repeats commands a specified number of times. You can use these features of Bash when writing interpreted programs called shell scripts.
This chapter shows you how to write simple shell scripts: a collection of shell commands stored in a file. Shell scripts are used to automate various tasks. For example, when your Red Hat Linux boots, many shell scripts stored in various subdirectories in the /etc directory (for example, /etc/init.d) perform many initialization tasks.
When it comes to writing scripts, the Perl language is also popular among UNIX system administrators. Because you probably are the system administrator of your Linux system, this chapter also introduces you to Perl scripting.
Chapter 25 covers Tcl/Tk, another popular scripting language you can use to build applications with a graphical interface.