FreeDNS updater script with IPv4 and IPv6 support

update-ip.sh

#!/bin/sh
#FreeDNS updater script with IPv4 and IPv6 support
# (Initially) based on update.sh by Adam Dean: https://freedns.afraid.org/scripts/update.sh.txt
# requirements:
#	curl
#	dig
#	posix-compatible shell

# Note: http://whatismyipaddress.com/api says:
#	"You may programmatically query that server but limit queries to no more
#	than once per five minutes and include an appropriate user agent that will
#	allow us to contact you if needed. Requests with a blank user agent may be
#	dropped."

# if you don't want to set the IPv4 or IPv6 address
#	then replace "_YOURAPIKEYHERE_" with an empty
#	string like this: ""
# TODO: pull all this from a config file
APIKEY_V4="_YOURAPIKEYHERE_"
APIKEY_V6="_YOURAPIKEYHERE_"
DOMAIN="_YOURDOMAINHERE_"
USER_AGENT='default'

update_url="https://freedns.afraid.org/dynamic/update.php?"

if [ "${USER_AGENT}" = 'default' ]; then
	curl_opts=""
else
	curl_opts="--user-agent ${USER_AGENT}"
fi

# FIXME:I have no idea how this will behave if
#	whatismyipaddress can't find an address
if [ -n "${APIKEY_V4}" ]; then
	registered_v4="$(dig +short @ns4.afraid.org ${DOMAIN} A)"
	current_v4="$(curl --silent ${curl_opts} http://ipv4bot.whatismyipaddress.com/)"
	if [ -n "${current_v4}" ]; then
		if [ "$current_v4" != "$registered_v4" ]; then
			curl "${update_url}${APIKEY_V4}&address=${current_v4}"
			echo "DNS A record changed to: $current_v4"
		fi
	fi
fi

if [ -n "${APIKEY_V6}" ]; then
	registered_v6="$(dig +short @ns4.afraid.org ${DOMAIN} AAAA)"
	current_v6="$(curl --silent ${curl_opts} http://ipv6bot.whatismyipaddress.com/)"
	if [ -n "${current_v6}" ]; then
		if [ "$current_v6" != "$registered_v6" ]; then
			curl "${update_url}${APIKEY_V6}&address=${current_v6}"
			echo "DNS AAAA record changed to: $current_v6"
		fi
	fi
fi