Programming Perl, 4th Edition

send

send SOCKET, MSG, FLAGS, TO
send SOCKET, MSG, FLAGS

This function sends a message on a socket. It takes the same flags as the syscall of the same name—see send(2). On unconnected sockets, you must specify a destination to send TO, which then makes Perl’s send work like sendto(2). The C syscall sendmsg(2) is currently unimplemented in standard Perl. The send function returns the number of characters sent, or undef if there is an error.

Note the characters: depending on the status of the socket, either (8-bit) bytes or characters are sent. By default, all sockets operate on bytes. But if, for example, the socket has been changed using binmode to operate with the :encoding(utf8) I/O layer, then its I/O will operate on UTF-8-encoded Unicode characters, not bytes.

(Some non-Unix systems improperly treat sockets as different from ordinary file descriptors, with the result that you must always use send and recv on sockets rather than the handier standard I/O operators.)

One error that at least one of us makes frequently is to confuse Perl’s send with C’s send and write:

send SOCK, $buffer, length $buffer;      # WRONG

This will mysteriously fail depending on the relationship of the string length ...