bash Cookbook

Why bash?

Why is this book about bash, and not some other shell? Because bash is everywhere. It may not be the newest, and it’s arguably not the fanciest or the most powerful (though if not, it comes close), nor is it the only shell that’s distributed as open source software, but it is ubiquitous.

The reason has to do with history. The first shells were fairly good programing tools, but not very convenient for users. The C shell added a lot of user conveniences (like the ability to repeat a command you just typed), but as a programming language it was quirky. The Korn shell, which came along next (in the early 80s), added a lot of user conveniences, and improved the programming language, and looked like it was on the path to widespread adoption. But ksh wasn’t open source software at first; it was a proprietary software product, and was therefore difficult to ship with a free operating system like Linux. (The Korn shell’s license was changed in 2000, and again in 2005.)

In the late 1980s, the Unix community decided standardization was a good thing, and the POSIX working groups (organized by the IEEE) were formed. POSIX standardized the Unix libraries and utilities, including the shell. The standard shell was primarily based on the 1988 version of the Korn Shell, with some C shell features and a bit of invention to fill in the gaps. bash was begun as part of the GNU project’s effort to produce a complete POSIX system, which naturally needed a POSIX shell.

bash provided the programming features that shell programmers needed, plus the conveniences that command-line users liked. It was originally conceived as an alternative to the Korn shell, but as the free software movement became more important, and as Linux became more popular, bash quickly overshadowed ksh.

As a result, bash is the default user shell on every Linux distribution we know about (there are a few hundred Linux distros, so there are probably a few with some oddball default shell), as well as Mac OS X. It’s also available for just about every other Unix operating system, including BSD Unix and Solaris. In the rare cases where bash doesn’t ship with the operating system, it’s easy to install. It’s even available for Windows (via Cygwin). It’s both a powerful programming language and a good user interface and you won’t find yourself sacrificing keyboard shortcuts to get elaborate programming features.

You can’t possibly go wrong by learning bash. The most common default shells are the old Bourne shell and bash, which is mostly Bourne shell compatible. One of these shells is certainly present on any modern, major Unix or Unix-like operating system. And as noted, if bash isn’t present you can always install it. But there are other shells. In the spirit of free software, the authors and maintainers of all of these shells share ideas. If you read the bash change logs, you’ll see many places where a feature was introduced or tweaked to match behavior on another shell. But most people won’t care. They’ll use whatever is already there and be happy with it. So if you are interested, by all means investigate other shells. There are many good alternatives and you may find one you like better—though it probably won’t be as ubiquitous as bash.