$listen()
$listen(<port> [family])

• The listen function establishes a passive TCP connection (``server'').
• The <port> argument is optional and if provided is taken as a number.
• If the <port> argument is not a number, the empty string is returned.
• If the <port> argument is not zero and less than 1024, the empty string is returned.
• The optional family argument can be 4, 6, v4, or v6, and tells the client whether it should bind to IPv4 or IPv6.
• If the requested port is not available (probably because it is in use by someone else), an error is output and the empty string is returned.
• The return value is the local port number associated with the connection.

If you want your script to act as an Internet server, the $listen() function lets you establish a place where others can $connect() to you. Once they $connect() to you, you are given a small integer that acts in the same way that $connect() return values do.

The port number being listened on, or the empty string on error.

$listen(1025)             returns 1025
$listen(1023)             error, returns nothing
$listen(0)                returns a system-allocated port number
$listen()                 returns a system-allocated port number

This function first appeared in ircII-2.2pre3