What the -w flag to the urbackupclientbackend command does

Anyone have a clue about the above? I’m trying to write an equivalent OpenRC script for the existing FreeBSD port rc.d script.

UPDATE: Found out what it does by running sudo /usr/local/sbin/urbackupclientbackend -help (Thanks, Mike Remski!) Among the output:

-w <path>,  --pidfile <path>
  Save pid of daemon in file