# incrontab -l
/tmp/dyn.example.com IN_CLOSE_WRITE /usr/local/bin/reload_dyn_zone.sh

reload_dyn_zone.sh (based on powerdns)

#!/bin/sh

/bin/cp -f /tmp/dyn.example.com /var/named/dyn.example.com
/usr/bin/pdns_control bind-reload-now dyn.example.com &> /dev/null