Linux® Command Line and Shell Scripting Bible

Chapter 8. Basic Script Building

IN THIS CHAPTER

• Building a script

• Stringing commands

• Storing variables

• Playing with math

• Redirecting output

• Checking codes

Now that we've covered the basics of the Linux system and the command line, it's time to start coding. This chapter discusses the basics of writing shell scripts. You'll need to know these basic concepts before you can start writing your own shell script masterpieces.

Using Multiple Commands

So far you've seen how to use the command line interface (CLI) prompt of the shell to enter commands and view the command results. The key to shell scripts is the ability to enter multiple commands, and process the results from each command, even possibly passing the results of one command to another. The shell allows you to chain commands together into a single step.

If you want to run two commands together, you can enter them on the same prompt line, separated with a semicolon:

$ date ; who
Mon Sep 24 19:44:35 EST 2007
rich    :0       2007-09-24 18:23 (console)
rich    pts/1    2007-09-24 18:24
rich    pts/0    2007-09-24 18:42
barbara pts/2    2007-09-24 19:30
katie   pts/3    2007-09-24 19:39
$

Congratulations, you just wrote a shell script! This simple script uses just two bash shell commands. The date command runs first, displaying the current date and time, followed by the output of the who command, showing who is currently logged on to the system. Using this technique, you can string together as many commands as you wish, up to the maximum command line character count of ...