There are a couple of things that will help with this sort of problem:

Always use strictures (use strict; use warnings;). They give an early warning about things going pear shaped and often provide the right information to figure out what the nature of the problem is.

Data::Dump::Streamer or Data::Dumper provide really useful ways of visualizing complicated data structures.

Of course reading the documentation that others have suggested will help a great deal too. Managing interesting data structures is at least as important to attaining Perl proficiency as knowing how to use Perl's regular expressions.