on !*:join:#channel: .notice # Hello $nick $+ , welcome to #
Note that noticing a message to the entire channel when a person joins, is generally considered lame. You should not use this in channels where you are not oped in.
The dot before the notice command, means the message will be silent. In other words, your bot or your own client, where you have loaded this code in, won't see it being said, but the rest of the people will. If you want to see it, remove the dot.