You might wonder why you ought to learn Bash programming. Well, here are a couple of compelling reasons:

You’re already running it 

If you check, you’ll probably find that you are running bash right now. Even if you changed your default shell, bash is probably still running somewhere on your system, because it’s the standard Linux shell and is used for a variety of purposes. Because bash is already running, any additional bash scripts that you run are inherently memory-efficient because they share memory with any already-running bash processes. Why load a 500K interpreter if you already are running something that will do the job, and do it well?

You’re already using it

Not only are you already running bash, but you’re actually interacting with bash on a daily basis. It’s always there, so it makes sense to learn how to use it to its fullest potential. Doing so will make your bash experience more fun and productive. But why should you learn bash programming? Easy, because you already think in terms of running commands, CPing files, and piping and redirecting output. Shouldn’t you learn a language that allows you to use and build upon these powerful time-saving constructs you already know how to use? Command shells unlock the potential of a UNIX system, and bash is the Linux shell. It’s the high-level glue between you and the machine. Grow in your knowledge of bash, and you’ll automatically increase your productivity under Linux and UNIX — it’s that simple.

Full articles here (source: funtoo linux):
Bash by Example, Part 1 – Fundamental programming in the Bourne-again shell
Bash by Example, Part 2 – More bash programming fundamentals
Bash by Example, Part 3 – Exploring the ebuild system