$ perl merge_keys.pl cyclic_test2.yml 
$VAR1 = {
          'key2' => {
                      'everyday' => 'apple',
                      'Z' => 'key2.Z',
                      'A' => [
                               {
                                 'zero' => '00'
                               },
                               {
                                 'Z' => 'key1.Z',
                                 'subkey_b' => 'qwer',
                                 'subkey_a' => 'asdf',
                                 'zero' => 0
                               },
                               {
                                 'A' => $VAR1->{'key2'}{'A'},
                                 'Z' => 'key2.Z',
                                 'everyday' => 'shuffling',
                                 'X' => 1,
                                 'zero' => 0,
                                 'Y' => 3000
                               }
                             ],
                      'X' => 1,
                      'zero' => 0,
                      'Y' => 2
                    },
          'key1' => {
                      'subkey_b' => 'qwer',
                      'Z' => 'key1.Z',
                      'subkey_a' => 'asdf',
                      'zero' => 0
                    },
          'key0' => {
                      'zero' => 0
                    },
          'key3' => {
                      'A' => $VAR1->{'key2'}{'A'},
                      'subkey_b' => 'qwer',
                      'subkey_a' => 'foo',
                      'X' => 1,
                      'Y' => 2,
                      'everyday' => 'apple',
                      'Z' => 'key1.Z',
                      'subkey_c' => 'bar',
                      'zero' => 0,
                      'deeper' => {
                                    'challenger' => 'deep',
                                    'zero' => 0
                                  }
                    }
        };