Code:
on *:text:!addcom *:#: {
  if ($nick isop #) && (!%addcom) {
    set -u15 %addcom .
    var %r = $read(commands.txt,ns,$2)
    if (%r) { .msg $chan [ $+ $nick $+ ]: Error, This command     $qt($2) is already exist into the database! | return }
    write commands.txt $2-
    msg $chan /me + Command $2 has been added to the database!
  }
}

This should work, but i didnt test it. As lon as %addcom exist the code halt, and it will be unset after 15 seconds.

And by the way, use the code tags when posting code, easyer so see the code that way. Start [ code ] end [ /code ] <- remove the spaces.

if ($me != tired) { return } | else { echo -a Get a pot of coffee now $+($me,.) }