use strict;
use warnings;

my %a = (one => [[],[],[]]);
print $#{$a{"one"}} + 1;

##</code><code>##

use Data::Dumper;

use strict;
use warnings;

my %a = (one => [ ['a','b'],['c','d'] ]);
print Dumper(@a{one});

##</code><code>##

$VAR1 = [
          [
            'a',
            'b'
          ],
          [
            'c',
            'd'
          ]
        ];