Perl5 リファレンス

               Receives a message on a socket.  Attempts to
               receive LENGTH bytes of data into variable SCALAR
               from the specified SOCKET filehandle.  SCALAR will
               be grown or shrunk to the length actually read.
               Takes the same flags as the system call of the
               same name.  Returns the address of the sender if
               SOCKET's protocol supports this; returns an empty
               string otherwise.  If there's an error, returns
               the undefined value.  This call is actually
               implemented in terms of recvfrom(2) system call.
               See the UDP: Message Passing entry in the perlipc
               manpage for examples.