Let's look at the following code. Up to counter1++ and forget the rest for now. with the conditions set (unless), I am taking those lines that are qualified. Counter1 gives me the number of counts for those lines (value for a hash). If I can iterate through $current_line14 >= and change the value of 3 (which is fixed here) I will get different counts. Therefore by each change at value of current_line14 >= you will get a different count. So your hash keys become your loop values from 3..30 for example and values will be the number of lines extracted. If I want to change "3" manually I have to perform the while loop 20 - 30 times for each key in order to get the counts.

while(<INPUT2>){
         chomp;
          my @current_line  = split /\t/;
     
          # eliminate unqualified lines early
     
next unless $current_line[5] == 1 && $current_line[14] >= 3;
         
          $counter1++;

     if ($file1{ $current_line[1]}) {
     my ($from, $to) = @{ $file1{ $current_line[1] } };
for ($from <= $current_line[2] && $current_line[2] <= $to) {

   print join("\t", $current_line[1],$current_line[5],$current_line[14
+], "***",$current_line[2]), "\n";

           $lines++;
            }
      }
}
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