Perl5 リファレンス

       shutdown SOCKET,HOW
               Shuts down a socket connection in the manner
               indicated by HOW, which has the same
               interpretation as in the system call of the same

                   shutdown(SOCKET, 0);    # I/we have stopped reading data
                   shutdown(SOCKET, 1);    # I/we have stopped writing data
                   shutdown(SOCKET, 2);    # I/we have stopped using this socket

               This is useful with sockets when you want to tell
               the other side you're done writing but not done
               reading, or vice versa.  It's also a more
               insistent form of close because it also disables
               the file descriptor in any forked copies in other