For anyone confused by this, 1 is the output to stdout, and 4 is being redirected to where 1 goes, which is stdout. Unrelated to that, 1 (what’s actually being output to stout by the application) is being redirected to /dev/null.

The order of operations matters. If 1 was redirected to /dev/null first, then 4 would also end up in /dev/null. As it stands now, that doesn’t happen.

"4>&1 1>/dev/null" means:

streams[4] = streams[1]; streams[1] = open("/dev/null");

The >& is for copying the descriptor not for aliasing ("hardlinking") it.

The descriptor is the "fd" argument, e.g.:

write(int fd, const void *buf, size_t count)