#!/bin/sh

if test "x$DYN_SERVER" = x; then echo export DYN_SERVER=ns.example.com; exit=1; fi
if test "x$DYN_DOMAIN" = x; then echo export DYN_DOMAIN=example.com; exit=1; fi
if test "x$DYN_SCRIPT" = x; then echo export DYN_SCRIPT=/path/to/script; exit=1; fi
if test "x$exit" = x1; then exit 1; fi

if test "x$DYN_IPAPI" = x; then DYN_IPAPI=ifconfig.co; fi

IPACTUAL=$(wget -qO - "$DYN_IPAPI")
IPSERVER=$(dig +short $DYN_DOMAIN @$DYN_SERVER)

if test "x$IPSERVER" = x -o "x$IPACTUAL" = x; then
	: # ERROR: IP unknown
elif test "x$IPSERVER" = "x$IPACTUAL"; then
	: # INFO: IP not changed
else
	"$DYN_SCRIPT" $IPACTUAL
fi