if($k_nuc eq $i_nuc){
                    $count->{$rel} ||= 0;
                    $count->{$rel}  += 1;
                }else{
                    $count->{$rel} ||= 0;
                    $count->{$rel}  += 0;
                }
                
=== possible change could be: =====
$count->{$rel} //= 0;  ### probably not needed, see below
if($k_nuc eq $i_nuc){                 
                       $count->{$rel}++;  
                    }