Unix: Old dog, new tricks part 2

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

rename will accept any regex and any perl operator