Y'know, it depends on what kind of testing problems that you are looking to solve. If you can identify what problem(s) you are trying to solve, then people can give better pointers to more pertinent information.
Is there any particular reason you are geared towards Unix or are you open to other tools?
You could look at Perl, from what I have read it works on the Unix platform as well as others. Several members of SQAforums do use this for their QA work. I am just starting to learn it myself. The book I found is "Perl programming for the Absolute beginner" by Jerry Lee Ford and if it is as good as his VBScript book I will be happy.
basically on *nix systems, when jobs for shell scripting become too big and complex.. the 2 alternate choices for that type of scripting is usually either Perl or Python (if you reach line 10 of your shell script, I would argue that you shouldn't be using shell at all).