Suspect that you aren't meant to run package.pl on its own, but main.pl is supposed to
do 'package.pl';

Back in the day, .pl stood for "perl library", and that's how you loaded your libraries. Nowdays, the preferred extension for loadable modules is .pm ("perl module"), and many people use .pl to stand for "perl script" (though on unix-y systems, scripts often have no extension).