Change filename CASE

There was time when I see some old files from DOS/WINDOWS with UPPERCASE letter and I wanted so bad to change the case but forgot the command, so I wrote it here so I know where to look again ;)

rumy@cbug-nest:~$ rename ‘y/A-Z/a-z/’ *
(assuming perl was installed on the system)

(or without perl)
rumy@cbug-nest:~$ for i in *; do mv $i `echo $i | tr [:upper:] [:lower:]`; done