Ison
From Scriptwiki
Checks if a certain nick, or list of nicks, are online / in use.
/ison <nick> [nick2] [nickN]
The result is returned through Raw 303 where $1 will be your nick and $2- will be a list of the nicks you specified that are online, or nothing. See working example below.
Example
The following example will modify the returned output of an /ison request to a more user-friendly format.
raw 303:*:{ if ($2) { echo -a User(s) $2- are online. } else { echo -a The user(s) specified are not online. } haltdef }