my @strings = ();
      open (my $F1, "<", $f1) || die "! open-100 $!";;  # open file 1 
      while ( my $input = <$F1> )
      {    chomp( $input ); # take off the line breaks
           $strings[$#strings] = $input;
      }
      close $F1;

##</code><code>##

      open (my $F3, ">", $f3 ) || die "! open-300 $!";