getsockname
See the current Perl documentation for getsockname.
Here is our local, out-dated (pre-5.6) version:
getsockname - retrieve the sockaddr for a given socket
getsockname SOCKET
Returns the packed sockaddr address of this end of the SOCKET connection.
use Socket; $mysockaddr = getsockname(SOCK); ($port, $myaddr) = unpack_sockaddr_in($mysockaddr);