snippet to show usage of dhcp-event (don't forget to set apparmor to allowing (complain) mode)

dhcpd.conf

subnet 192.168.0.0 netmask 255.255.255.0 {
	range 192.168.0.100 192.168.0.200;
	option broadcast-address 192.168.0.255;
	option routers 192.168.0.1;
	on commit {
		set ClientIP = binary-to-ascii(10, 8, ".", leased-address);
		set ClientMac = binary-to-ascii(16, 8, ":", substring(hardware, 1, 6));
		log(concat("Commit: IP: ", ClientIP, " Mac: ", ClientMac, "Hostname: ", host-decl-name));
		execute("/usr/local/bin/dhcp-event", "commit", ClientIP, ClientMac, host-decl-name);
	}
	on release {
		set ClientIP = binary-to-ascii(10, 8, ".", leased-address);
		set ClientMac = binary-to-ascii(16, 8, ":", substring(hardware, 1, 6));
		log(concat("Release: IP: ", ClientIP, " Mac: ", ClientMac, "Hostname: ", host-decl-name));
		execute("/usr/local/bin/dhcp-event", "release", ClientIP, ClientMac, host-decl-name);
	}
	on expiry {
		set ClientIP = binary-to-ascii(10, 8, ".", leased-address);
                set ClientMac = binary-to-ascii(16, 8, ":", substring(hardware, 1, 6));
                log(concat("Expiry: IP: ", ClientIP, " Mac: ", ClientMac, "Hostname: ", host-decl-name));
                execute("/usr/local/bin/dhcp-event", "expiry", ClientIP, ClientMac, host-decl-name);
	}
}

gistfile2.txt