use strict;
use warnings;
use feature qw( say );

my @aa = qw(A C D E F G H I K L M N P Q R S T V W Y);
my $pair;

for my $n1 (@aa)
{
    for my $n2 (@aa)
    {
        $pair = $n1 . $n2;    
        say $pair;
    }
}

##</code><code>##

use strict;
use warnings;
use feature qw( say );

my @aa = qw(A C D E F G H I K L M N P Q R S T V W Y);
my @pairs;

for my $n1 (@aa)
{
    for my $n2 (@aa)
    {
        push @pairs, $n1 . $n2;
    }
}

say for @pairs;