#!/usr/bin/perl -w
use strict;

my $str="BATCATDATEFEAT";

my $A=0;
my $T=0;
while ($str =~ /A/ig) {
   $A++;# Line 4
   print "\n A=$A ends at ",pos $str,"\n";
}

while ($str =~ /T/ig) {
   $T++;
   print"\n T=$T ends at ",pos $str,"\n";
}

my $output="Results.txt";                 # Line 8 
open(my $fh, ">", $output) or die "Cannot open file '$output'.\n\n";

$A=0;
$T=0;
while ($str=~ /A/ig) {
   $A++;
   print $fh "\n A=$A ends at ",pos $str,"\n";
}

while ($str=~ /T/ig) {
   $T++;
   print $fh "\n T=$T ends at ",pos $str,"\n";
}