[<channel>] [--{exact,nick,user,host}] <nick> [<seconds>]
If you have the #channel,op capability, this will ban <nick> for
as many seconds as you specify, otherwise (if you specify 0 seconds or
don't specify a number of seconds) it will ban the person indefinitely.
--exact can be used to specify an exact hostmask. You can combine the
exact, nick, user, and host options as you choose. <channel> is only
necessary if the message isn't sent in the channel itself.