If you need to rename a larger number of files following a certain pattern then you will long for an automated solution. The 'rename' command helps you here that is (at least on my Debian installation) part of the Perl installation. All you need to know is the basics of regular expressions to define how the renaming should happen.
Say you want 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' *
Or you want to make the filenames lowercase:
rename 'tr/A-Z/a-z/' *
Or you want to remove all double characters:
rename 'tr/a-zA-Z//s' *
Or 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.