bash is a shell: a command interpreter. The main purpose of bash (or of any shell) is to allow you to interact with the computer’s operating system so that you can accomplish whatever you need to do. Usually that involves launching programs, so the shell takes the commands you type, determines from that input what programs need to be run, and launches them for you. You will also encounter tasks that involve a sequence of actions to perform that are recurring, or very complicated, or both. Shell programming, usually referred to as shell scripting, allows you to automate these tasks for ease of use, reliability, and reproducibility.
In case you’re new to bash, we’ll start with some basics. If you’ve used Unix or Linux at all, you probably aren’t new to bash—but you may not have known you were using it. bash is really just a language for executing commands—so the commands you’ve been typing all along (e.g., ls, cd, grep, cat) are, in a sense, bash commands. Some of these commands are built into bash itself; others are separate programs. For now, it doesn’t make a difference which is which.
We’ll end this chapter with a few recipes on getting bash. Most systems come with bash pre-installed, but a few don’t. Even if your system comes with bash, it’s always a good idea to know how to get and install it—new versions, with new features, are released from time to time.
If you’re already running bash, and are somewhat familiar with it, you may want to go straight to Chapter 2. You are not likely to read this book in order, and if you dip into the middle, you should find some recipes that demonstrate what bash is really capable of. But first, the basics.
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