use warnings;
use strict;

my %hash = (4 => 12, 34 => 102);

while (my ($k, $v) = each %hash){
    print "$k => $v\n";
}
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In other words, each() returns two scalar items. What's happening in your case, is that @k is taking both items being returned for each hash key/value pair on each iteration, so there's nothing ever in the @v array. Use scalars like I have instead.