If you haven't done so already, take a look at perldata.

Also, (again, if this is new to you), look into using Data::Dumper.  It's a fantastic, simple way of verifying exactly what a given data structure looks like.

For example:

use strict;
use warnings;

use Data::Dumper;

my $pdata = {
    'red'  => [ 'abc', 'def', 'ghi' ],
    'blue' => { '123' => '456', 'xxx' => 'yyy' },
};

print "Dump of pdata = ", Dumper($pdata), "\n";
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which prints:

Dump of pdata = $VAR1 = {
          'blue' => {
                      '123' => '456',
                      'xxx' => 'yyy'
                    },
          'red' => [
                     'abc',
                     'def',
                     'ghi'
                   ]
        };
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And that tells you that you have a hash ($pdata) containing two keys, 'blue' and 'red', where 'blue' is a pointer to a hash containing two keys and two values, and 'red' is a pointer to an array containing 3 values.