That's not what was requested, that would join the channel #nillen in case I were to type it. He requested for it to be "!join nillen" instead, which requires the $2 identifier.
# will not refer to #botname unless the channel it is written in is the same as the botname either, it will simply return the channel name of the channel.
In this case, this would also be wrong. You can join a channel by typing /join nillen, which would make you join #nillen, however, if you have that in your script, and someone would join #nillen, it would turn out as ##nillen, which would be wrong.
