fcntl function. You'll probably have to say
use Fcntl;
first to get the correct function definitions. Argument processing and
value return works just like ioctl below. Note that
fcntl will produce a fatal error if used on a machine that
doesn't implement fcntl. For example:
use Fcntl;
fcntl($filehandle, F_GETLK, $packed_return_buffer);