$template  = "index.txt";
$counter   = "counter.txt";
$pos   = 0;
$found = 0;
$num   = 0;


  open (F1, "+>$template");
   @idxlines = <F1>;
    close F1;

     foreach $lines (@idxlines) {

        if ($lines =~ /<% INCLUDE  file2.txt %>/) {
            $found = 1;
              last;
          }
       $pos++;
     }


  open (F1, "+<$template");

    open (CT, "$counter");
     $num = <CT>;
    close CT;

   if ($num == 2) { $num = "1" } else { $num++ }

    open(CT, ">$counter");
      print CT $num;
    close CT;

    $idxlines[$pos] = "<% INCLUDE file$num.txt %>";
     print F1 $idxlines[$pos];
    close F1;