Shell Scripting: Expert Recipes for Linux, Bash, and More

Summary

Functions are a convenient way to package sections of code in a flexible, modular, and reusable format. Functions are called in much the same way as shell scripts and other commands, and parse their arguments in exactly the same way as a shell script — $1, $2, $3, $*, as well as getopts all work the same way in a function as in a shell script. This makes it quite easy to convert an existing script into a function, and vice-versa.

Putting groups of related functions together in libraries extends the language and effectively provides customized commands tailored for the particular task at hand. Libraries make programming easier, more abstract, and more convenient, taking implementation detail away from the script and hiding it in a more suitable location. This makes changing the way the library works transparent, making changes and upgrades to the underlying methods seamless.

Arrays are a special type of variable which can be very flexible, although they do not work very well with functions. This is all covered in the next chapter.