Receives a message on a socket. Attempts to receive LENGTH characters 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 the recvfrom(2) system call. See "UDP: Message Passing" in perlipc for examples.
Note the characters: depending on the status of the socket, either (8-bit) bytes or characters are received. By default all sockets operate on bytes, but for example if the socket has been changed using binmode to operate with the :encoding(utf8) I/O layer (see the open pragma), the I/O will operate on UTF8-encoded Unicode characters, not bytes. Similarly for the :encoding layer: in that case pretty much any characters can be read.