The GNU Bourne-Again Shell, or Bash, is the best-known Bourne-style shell in the world, and is installed or available for installation on a huge variety of Unix-like systems. Even professionals who don't do a lot of work with Unix or Linux will need to use the Bash shell occasionally.
Bash is a language of contradictions; while it's the best-known and most widely-deployed shell of its kind, it's perhaps also one of the least-understood tools, with a terse syntax that's relatively unique among modern programming languages and can seem bizarre even to experienced users. Bash is powerful in some ways, and very limited in others. It's clear, elegant, and expressive in some ways, and terse, clumsy, and bewildering in others.
Because it's so powerful and yet so complex, and because so many computer professionals can't avoid using it at least occasionally, Bash is often learned by way of a kind of "tradition;" demonstrations by experienced administrators, reading others' scripts, copying and pasting, and asking questions and reading answers on the internet. This leads to a lot of "cargo-cult programming," and a lot of bad practices that make things unnecessarily confusing at best, and downright dangerous at worst. The available documentation for Bash is often unhelpful in addressing this problem—it often teaches the same bad practices, and even when it's correct, as the official Bash manual page is, it's often too complicated and assumes too much knowledge for new users to understand it.
To avoid all that, we'll start learning good Bash from first principles, and focus almost exclusively on writing the language well, in both interactive and batch mode. By the end of this book, you'll have a firm grasp on how to write Bash shell script in a robust and understandable way, and be in a position to notice bad habits and dangerous "hot spots" in others' code. You'll have a great grasp on the problems for which shell script is a perfect solution, and writing it will be a lot more efficient, and maybe even fun.