how to specify pid file ? (for newsyslog)

hi, on freebsd I need to specify pid file in order to send a signal to rotate log: /etc/newsyslog.conf: /var/log/bird.log 600 7 100 @0101T JC /var/run/bird.pid SIGHUP ... is there a way to write a pid to file ? I haven't found any Cheers, Ilya Shipitsin