many monks above have provided the wisdom you seek. see perlref and perlsub for more details.

i want to comment on your use of 'strict programming rules'. the code you provide does not use strict. this, along with warnings (-w on pre-5.006 perls) is your best defense against common programming mistakes. see Use strict warnings and diagnostics or die for more info.

also, you should be careful when using the & sigil. you must understand its behaviour, as it does not perform as you probably expect. if called with no parenthesis, as in &callsub;, the current @_ is passed automatically. also, it will override your prototypes, if you're using them (but you probably shouldn't be). see perlsub for much, much more on that.

~Particle *accelerates*