Current Perl documentation can be found at perldoc.perl.org.
Here is our local, out-dated (pre-5.6) version:
If you're lucky enough to be using a system that supports non-blocking reads (most Unixish systems do), you need only to use the
O_NONBLOCK flag from the Fcntl module in conjunction with
use Fcntl; sysopen(FH, "/tmp/somefile", O_WRONLY|O_NDELAY|O_CREAT, 0644) or die "can't open /tmp/somefile: $!":