Command line parsing is a common problem so, not surprisingly, someone's already solved it for you.
There's an entire hierarchy on CPAN dedicated to this, called
Getopt. A couple of the more popular modules are:
Browse the documentation, and see which one suits your needs.
For any problem in Perl that might have a general solution, it's worthwhile having a look on CPAN. Chances are there's a module that does all the work for you. This is one of the best parts of Perl.