The zsh contains a very usefull extension called zmv. You can load it via
autoload -U zmv. The man page is located under zshcontrib. A very usefull flag is
-n which does not execute the command but prints the command that would be executed. Use this if you are unsure about your patterns.
Here are two simple examples:
Replace all spaces in filenames with underscores.
zmv '* *' '$f:gs/ /_'
Rename all files according to a pattern.
zmv '*.(*).(*).([0-9][0-9])*.mkv' '$1_$2-$3.mkv'
This one renames all files matching