Synopsis:
   $listen([<port>])

Technical:
   This function causes the client to bind to the given TCP port and listen
   for incoming connections.  The client is not permitted to listen to any
   port below 1025; they are reserved for privileged system use.  If no
   port is given, the system allocates an arbitrary port above 1024.

Practical:
   This function makes the client listen to the given port.  This allows,
   theoretically, someone to connect to that port to use whatever services
   you have scripted for it.  This could be used for something simple,
   such as a daytime or motd generator, or something more complex like a
   file server.

Returns:
   port number bound to, or nothing if error

Examples:
   $listen(1025)             returns 1025
   $listen(1024)             error, returns nothing
   $listen()                 returns a system-allocated port number

See Also:
   connect(6); dcc(1) close, raw; on(5) dcc_raw