The rename command which is part of the Perl installation helps.

All you need to know is the basics of regular expressions to define how the renaming should happen.

To add a '.old' to every file in your current directory. At the end of each expression ($) a '.old' will be set:

rename 's/$/.old' *

To make the filenames lowercase:

rename 'tr/A-Z/a-z/' *

To remove all double characters:

rename 'tr/a-zA-Z//s' *

You have many JPEG files that look like “img0000154.jpg” but you want the first five zeros removed as you don’t need them:

rename 's/img00000/img/' *.jpg

In fact you can use any Perl operator as an argument.

The actual documentation for the 's' and 'y'/'tr' operators are found in the 'perlop' manpage.