perl shutdown a socket

Question

Is there a difference between

shutdown($socket, 0) if $socket;
shutdown($socket, 2) if $socket;
close($socket) if $socket;

and

shutdown($socket, 2) if $socket;
close($socket) if $socket;

Also is there a difference between

shutdown($socket, 1) if $socket;
shutdown($socket, 2) if $socket;
close($socket) if $socket;

and

shutdown($socket, 2) if $socket;
close($socket) if $socket;

And finally is the close needed at all?

Answer 1

shutdown causes one side of the TCP connection to stop reading (0), or writing (1), or both (2). So the first two snippets have the same effect, as do the next two.

shutdown does not release the file descriptor, so close is still needed.

The difference between single close and one preceded by shutdown( fd, 2 ) is that in the second case TCP will not try to deliver outstanding data to the remote side (see SO_LINGER).