your code does not work as you might expect. you will get an array qw/4 2/. you have to push a reference in @arr:

use Data::Dumper;
@alpha = qw/a b c d/;
@beta = qw/e f/;
$arr[0] = \@alpha;
$arr[1] = \@beta;
print Dumper(@arr);

print scalar @{$arr[0]};
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