$ cat t.pl
#/usr/bin/perl
use strict;
use warnings;
use Data::Dumper;

my @a = (1, 2, 3);

print "Size of a: ", scalar(@a), "\n";
print Dumper(\@a),"\n";

my @b = [0, 1, 2];
print "Size of b: ", scalar(@b), "\n";
print Dumper(\@b),"\n";

print "Size of b[0]: ", scalar(@{$b[0]}), "\n";
print Dumper($b[0]),"\n";

##</code><code>##

$ perl t.pl
Size of a: 3
$VAR1 = [
          1,
          2,
          3
        ];

Size of b: 1
$VAR1 = [
          [
            0,
            1,
            2
          ]
        ];

Size of b[0]: 3
$VAR1 = [
          0,
          1,
          2
        ];