Regular Expressions in Action

Now that you've seen the rules and a few simple demonstrations of using regular expression patterns, it's time to put that knowledge into action. The following sections demonstrate some common regular expression examples within shell scripts.

Counting directory files

To start things out, let's look at a shell script that counts the executable files that are present in the directories defined in your PATH environment variable. To do that, you need to parse out the PATH variable into separate directory names. Chapter 6 showed you how to display the PATH environment variable:

$ echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games
$

Your PATH environment variable will differ, depending on where the applications are located on your Linux system. The key is to recognize that each directory in the PATH is separated by a colon. To get a listing of directories that you can use in a script, you must replace...