rename is a script which renames files according to a perl expression.
Apparently Larry Wall wrote such a script years ago (with almost identical syntax to mine! great minds think alike!), but I didn't know that or I wouldn't have reinvented the wheel. If I do say so, this version's a bit better, and safer when it comes to clobbering your files.
% rename 's/\.bak$//' *.bak # strips the .bak off all .bak files
% rename 's/\d+$/$&+1/e' messages.* # incremements numeric suffixes
% rename '$_ .= "-" . time()' log* # adds -seconds-since-epoch to files