Learning the bash Shell, Second Edition

Chapter 4. Basic Shell Programming

If you have become familiar with the customization techniques we presented in the previous chapter, you have probably run into various modifications to your environment that you want to make but can’t—yet. Shell programming makes these possible.

bash has some of the most advanced programming capabilities of any command interpreter of its type. Although its syntax is nowhere near as elegant or consistent as that of most conventional programming languages, its power and flexibility are comparable. In fact, bash can be used as a complete environment for writing software prototypes. ^[48]

Some aspects of bash programming are really extensions of the customization techniques we have already seen, while others resemble traditional programming language features. We have structured this chapter so that if you aren’t a programmer, you can read this chapter and do quite a bit more than you could with the information in the previous chapter. Experience with a conventional programming language like Pascal or C is helpful (though not strictly necessary) for subsequent chapters. Throughout the rest of the book, we will encounter occasional programming problems, called tasks, whose solutions make use of the concepts we cover.

Shell Scripts and Functions

A script, which is a file that contains shell commands, is a shell program. Your .bash_profile and environment files, discussed in the previous chapter, are shell scripts.

You can create a script using the text ...