Linux Command Line and Shell Scripting Bible, 4th Edition

CHAPTER 17Creating Functions

IN THIS CHAPTER

• Exploring basic script functions
• Returning a value from a function
• Using variables in functions
• Investigating array variables and functions
• Considering function recursion
• Creating a library
• Using functions on the command line

Often while writing shell scripts, you'll find yourself using the same code in multiple locations. If it's just a small code snippet, it's usually not that big a deal. However, rewriting large chunks of code multiple times in your shell script can get tiring. The Bash shell provides a way to help you out by supporting user-defined functions. You can encapsulate your shell script code into a function and use it as many times as you want, anywhere in your script. This chapter walks you through the process of creating your own shell script functions and demonstrates how to use them in other shell script applications.

Exploring Basic Script Functions

As you start writing more complex shell scripts, you'll find yourself reusing parts of code that perform specific tasks. Sometimes, it's something simple, such as displaying a text message and retrieving an answer from the script users. Other times, it's a complicated calculation that's used multiple times in your script as part of a larger process.

In each of these situations, it can get tiresome writing the same blocks of code over and over in your script. It would be nice to just write the block of code once and be able to refer to that block of code anywhere ...