[Filligree]

For this in particular, try the Advanced Bash Scripting doc, http://www.tldp.org/LDP/abs/html/

There's a bunch of interesting constructs there. Most of them also apply to improved shells such as zsh, though some are just pointless there.

[AceJohnny2]

I've seen the ABS guide criticized for being obsolete and recommending wrong or obsolete best practices. A recommended replacement is The Bash Hacker's Wiki: http://wiki.bash-hackers.org/doku.php

Which itself recommends as best (current) alternative: Greg's Bash Guide: http://mywiki.wooledge.org/BashGuide