Getting Started with shell programming

HOWTO Guides

Advanced Bash Scripting Guide - Recommended. A fairly thorough introduction.

BASH Programming - Introduction HOW-TO - Short and not very clear. Be careful with the examples

Books on shell programming

Many books exist. One reasonable example is:

Classic Shell Scripting by Nelson H.F. Beebe, Arnold Robbins. Publisher: O'Reilly
"Writing shell scripts requires more than just a knowledge of the shell language, it also requires familiarity with the individual Unix programs: why each one is there, how to use them by themselves, and in combination with the other programs. The authors are intimately familiar with the tips and tricks that can be used to create excellent scripts, as well as the traps that can make your best effort a bad shell script. With Classic Shell Scripting you'll avoid hours of wasted effort. You'll learn not only write useful shell scripts, but how to do it properly and portably." (Available from the MIT O'Reilly Online Library)