open(OUT, '>', 'index.txt') or die($!);
   &byfile; # subroutine to find, analyze, & write filenames
   printf STDERR ("%d lines processed\nwith header, " .
      "%d lines written to index.txt", $lines, $lines + 1);
   close(OUT);
   system("notepad index.txt");
   system("index.xlsx");