Arrays in Perl don't have fixed dimensions. If you have a 2D array (actually an array of references to arrays), it is quite possible that each second level array has a different number of elements.

Here is some code to print the number of elements in each second level array in such a data structure. The concept is easily extendable to three dimensions.

my @AoA = (['the', 'first', 'array'],
           ['another', 'array'],
           ['this', 'is', 'the', 'last', 'one']);

foreach (@AoA) {
  print scalar @$_, " elements\n";
}
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This prints out:

3 elements
2 elements
5 elements
[download]

Originally posted as a Categorized Answer.