In a perl array of arrays, just like in C, the data structure does not have to be rectangular (or cuboidal, or ...). For example, you can have an array like so:

@foo = (
    [0, 1, 2, 3, 4, 5],
    [0, 1, 2],
    [0, [ 0, 1, 2, 3 ]]
);
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There, @foo contains three references to arrays, all of which are of different lengths. One of them contains a reference to another array as well as an ordinary scalar. The following code will tell you the largest number of elements in each dimension. Dimensions are numbered starting at zero (I assume $[ has not been altered):

my @foo = (
    [0, 1, 2, 3, 4, 5],
    [0, 1, 2],
    [0, [ 0, 1, 2, 3 ]]
);

my @maxlength = ();
figger_out_depth(0, @foo);

print "max dimensions:\n";
print "  $_: $maxlength[$_]\n" foreach (0..$#maxlength);

sub figger_out_depth {
    my $depth = shift;
    $maxlength[$depth] = 0 unless(defined($maxlength[$depth]));
    foreach my $element (@_) {
        figger_out_depth($depth + 1, @{$element}) if(ref($element) eq 
+'ARRAY');
    }
    $maxlength[$depth] = $#_ + 1 if($#_ >= '0'.$maxlength[$depth]);
}
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