my %hash;
my $hashref = \%hash;
$hash{key1} = { key1_1 = ["value1_1",value1_2"],
                key1_2 = "w00t!",
              };
$hash{key2} = { key2_1 = "wakkawak!", 
                key2_2 = $hashref->{key1}{key1_1}, 
              };