Guest thegreatonech

[...]
@pq: (The first with the second, the third with the forth...) with this I mean the keys of the hash which are from 0 to 511. so i have to put key "0" with key "1" , key "2" with key "3" ...
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use 5.012;

my %hash = ( 0 => 'aa', 1 => 'bb', ... );

my $count = 512;
my $_;

for (0 .. ($count / 2)) {
  my $i = 2 * $_;

  say hex($hash{$i} . $hash{$i + 1});
}