Linux® Bible 2011 Edition: Boot up to Ubuntu®, Fedora®, KNOPPIX, Debian®, openSUSE®, and 13 Other Distributions

Chapter 14. Creating Useful Shell Scripts

IN THIS CHAPTER

• Understanding shell scripts

• Executing and debugging shell scripts

• Performing arithmetic in shell scripts

• Using programming constructs in shell scripts

• Trying simple shell scripts

You'd never get any work done if you typed every command that needs to be run on your Linux system when it starts. Likewise, you could work more efficiently if you grouped together sets of commands that you run all the time. Shell scripts can handle these tasks.

A shell script is a group of commands, functions, variables, or just about anything else you can use from a shell. These items are typed into a plaintext file. That file can then be run as a command. Most Linux systems use system initialization shell scripts during system startup to run commands needed to get services going. You can create your own shell scripts to automate the tasks you need to do regularly.

This chapter provides a rudimentary overview of the inner workings of shell scripts and how they can be used. You learn how shell scripts are responsible for the messages that scroll by on the system console during booting and how simple scripts can be harnessed to a scheduling facility (such as cron or at) to simplify administrative tasks.

Understanding Shell Scripts

Have you ever had a task that you needed to do over and over that took a lot of typing on the command line? Do you ever think to yourself, "Wow, I wish there was just one command I could type to do all this of this"? Maybe a shell ...