Sounds like your just starting out, and merlyn answered your prccise question. However you should be aware of some conventions you should adopt from the beginning:

1. When developing scripts invoke perl with the -w flag. This will turn warnings on that are visible at compile time that are very helpful at writing clean code.
2. As soon as you get comfortable with Regular Expressions turn on the -T flag. This will put perl in 'Taint checking' mode and will force you to explicitly 'OK' information given to the program from outside the scope of your code (ie input).
3. The other convention that helps to keep variables from getting out of control (Not having to declare variables can make it almost too easy to keep track of the variables scope(s)); is to declare "use strict" near the beginning of your scripts.

I should also add that once your happy with the scripts to take these flags out of the she-bang line for faster execution

A final word of caution: Perl is very addicting