It might be easier to just /play the file smile
Code:
on *:text:!commands:#: {
  if ($file(commands.txt)) { .play # commands.txt 2000 }
}

.play # commands.txt 2000
play msgs the file contents one line at a time.
The 2000 refers to milliseconds delay between each line (2000 ms = 2 seconds), you can change that as you wish.

For more options, see "/help /play" (especially the second option that pops up when typing that).