Perl: How to Construct "Array of Array" Data Structure

How can we express the data structure of "Array of Array" in Perl? Usually we create a generic array in Perl like this: @array = ('aaa', 'bbb', 'ccc'). Please take a look at the sample code shown below.

Note that a vaiable $songs starts with '$'. Also note that parenthesis is [...], not (...), even it is inside the parenthesis. This is to express a "reference" of "Array of Array". Take a look at "foreach" for accessing the reference variable.

#!/usr/bin/perl

my $songs = [
  [
    'S3T-party_people.mp3'  ,
    '3MN-ill_do_my_best.mp3',
    'CU2-gamusha_life.mp3'  ,
    'A3N-kaerimichi.mp3'    ,
  ],
  [
    '4YK-tokyo_zekkei.mp3'              ,
    'BM3-karate.mp3'                    ,
    'DE9-ashita_chikyuu_ga_konogoma.mp3',
    'R3-bright_fantasy.mp3'             ,
  ],
  [
    'IR3-realize.mp3'                        ,
    'MCZ-hakkin_no_yoake.mp3'                ,
    '8AS-itsu_ka_mita_niji_no_sono_shita.mp3',
    'WG3-shoujo_koukyoukyoku.mp3'            ,
  ],
];

my $song_list = $songs->[1]; # Access to the second array set

foreach my $song (@$song_list) { # Put '@' before a variable $song_list

  print "$song\n";
}

1;

Here is the output.

4YK-tokyo_zekkei.mp3
BM3-karate.mp3
DE9-ashita_chikyuu_ga_konogoma.mp3
R3-bright_fantasy.mp3