Any recommended resources for shell scripting on macs?

Somebody wants me to shell script something for his Mac. I don't even script on my 开发者_开发问答Linux, and I'm not even sure what shell to expect on a Mac. What are some good resources for starting Mac shell scripting? Or any viable alternatives you can think of - as long as it doesn't require 3rd party software.

http://developer.apple.com/internet/opensource/opensourcescripting.html

The shells on the Mac are the same ones you'd find on Linux; bash, tcsh, ksh, and zsh are installed by default.