use warnings;
@array = qw(A T C G);
$word_length = 3;

$max = ($#array+1)**$word_length;

$mainc = 0;
$count1 = 0; 
$count2 = 0; 
$count3 = 0; 

while ($mainc != $max){
  
print $array[$count1];  
print $array[$count2];
print $array[$count3];

$count1++;

if ($count1 == $#array){
    $count1 = 0;
    $count2++;
    }

if ($count2 == $#array){
    $count2 = 0;
    $count3++;
    }

if ($count3 == $#array){
    $count3 = 0;
    }

print "\n";
$mainc++;
    }