Well, my isn't the only way to declare a variable and stop use strict 'vars' from complaining. Other ways include use vars, local and using fully qualified variable names (e.g. $main::foo).

In general, the difference between package variables (that live in a typeglob) and lexical variables (which don't) is a very deep magic that lies at the heart of a thorough knowledge of Perl. I recommend a close study of the Variables section of the Camel book (3ed).

"Perl makes the fun jobs fun
and the boring jobs bearable" - me