# filename format: filename-timestamp-counter.txt

  # assumption: $ts contains timestamp in unix time format 
  #   (seconds since epoch)
  # assumption: $filename created earlier with 'my',
  #   and will contain the filename at end

  my @fnp = ('file', $ts, 0);
  $fnp[2]++ while (-e join('-', @fnp));
  $filename = join('-', @fnp) . '.txt';