Whenever I start using any data structures, I use Data::Dumper profusely. Data::Dumper will simply print out the entire data structure with the proper reference notation. It is a great way to start debugging scripts when you dont understand the data you are dealing with. Of course lhoward's advice is definately more valuable: use strict. Here is an example of Data::Dumper

use Data::Dumper;

my %hash = ('a'=>1, 'b'=>2, 'b'=>3);
my @array = ('c','d','e','f');

my $data = {%hash};
$data->{'array'} = [@array];
$data->{'array'}[4] = {%hash};
$data->{'array'}[4]{'foobar'} = [@array];

print Data::Dumper->Dump([$data], ['data']);
[download]

Results:

$data = {
          'a' => 1,
          'b' => 3,
          'array' => [
                       'c',
                       'd',
                       'e',
                       'f',
                       {
                         'foobar' => [
                                       'c',
                                       'd',
                                       'e',
                                       'f'
                                     ],
                         'a' => 1,
                         'b' => 3
                       }
                     ]
        };
[download]

And you can use it to print out any unknown object, such as a CGI object:

use CGI qw(:standard -debug);
my $cgi = new CGI;
print Data::Dumper->Dump([$cgi], ['cgi']);
[download]

I entered in values of 'foobar=val, and 'submit=sumbit' and the Results:

$cgi = bless( {
                '.charset' => 'ISO-8859-1',
                'foobar' => [
                              'val'
                            ],
                '.parameters' => [
                                   'foobar',
                                   'submit'
                                 ],
                'submit' => [
                              'sumbit'
                            ],
                '.fieldnames' => {}
              }, 'CGI' );
[download]

The notations for {} mean hash references and the notation for [] is for array references.