A shell script to update the public IP address of a Google DynDNS hostname.

update-google-dyndns.sh

#!/bin/bash

# Google Domains provides an API to update a DNS "Synthetic record". This script
# updates a record with the script-runner's public IP, as resolved using a DNS
# lookup.
#
# Google Dynamic DNS: https://support.google.com/domains/answer/6147083
# Synthetic Records: https://support.google.com/domains/answer/6069273
# Original script: https://gist.github.com/cyrusboadway/5a7b715665f33c237996
# Original modified script: https://gist.github.com/drewchapin/57d7039e30e8cc49e30bdc56a194f5bf
# To automate this, run command "crontab -e" to edit crontab, and add the line
# "*/15 * * * * sh pathtoscript" without quotes to run every 15 minutes.

USERNAME=""
PASSWORD=""
HOSTNAME=""
LOG_FILE="/tmp/ddns/log.log"
LOG_IP_FILE="/tmp/ddns/ip.log"
PUBLIC_IP=$(curl -s "https://checkip.amazonaws.com/")
DDNS_IP=$(cat ${LOG_IP_FILE})
if [[ "$PUBLIC_IP" != "$DDNS_IP" ]]; then
	echo "`date`: New public IP is \"${PUBLIC_IP}\" while old public IP was \"${DDNS_IP}\"." >> ${LOG_FILE}
	URL="https://domains.google.com/nic/update?hostname=${HOSTNAME}&myip=${PUBLIC_IP}"
	RESP=$(curl -s -k --user "${USERNAME}:${PASSWORD}" "$URL")
	case $RESP in
		"good ${PUBLIC_IP}" | "nochg ${PUBLIC_IP}")
			echo $PUBLIC_IP > ${LOG_IP_FILE}
			echo "`date`: ${HOSTNAME} successfully updated to ${PUBLIC_IP}." >> ${LOG_FILE}
			;;
		"nohost")
			echo "`date`: The host ${HOSTNAME} does not exist, or does not have Dynamic DNS enabled." >> ${LOG_FILE}
			;;
		"badauth")
			echo "`date`: The username / password combination is not valid for the host ${HOSTNAME}." >> ${LOG_FILE}
			;;
		"notfqdn")
			echo "`date`: The supplied hostname ${HOSTNAME} is not a valid fully-qualified domain name." >> ${LOG_FILE}
			exit
			;;
		"badagent")
			echo "`date`: Your Dynamic DNS client is making bad requests. Ensure the user agent is set in the request." >> ${LOG_FILE}
			exit
			;;
		"abuse")
			echo "`date`: Dynamic DNS access for the hostname ${HOSTNAME} has been blocked." >> ${LOG_FILE}
			exit
			;;
		"911")
			echo "`date`: An error happened on Googles end. Wait 5 minutes and retry." >> ${LOG_FILE}
			;;
		*)
			echo "`date`: $RESP" >> ${LOG_FILE}
	esac
#else
#	echo "`date`: Everything's good." >> ${LOG_FILE}
fi

l20: DDNS_IP=$(echo ${LOG_IP_FILE})

Change echo by cat, else the following if will always be true cause value of DDNS_IP would be "/tmp/ddns/ip.log" and PUBLIC_IP something like 255.255.255.255

Not sure I fully understand.
Do you mean "change echo to cat"?
So line 20 would read, DDNS_IP=$(cat ${LOG_IP_FILE})?

Yep

OK thanks. I would appreciate any other suggestions or if there's anything better to use since I'd rather not maintain this if I don't have to. I'm not a particularly big fan of Google or anything.

No problems, thanks for the this script. I don't have anything to add since it look like to work well ;)

I should have included instructions on how to find out if this script is still running and how to look at the log because I don't remember anymore LOL

I found out it wasn't logging unless you touch the log files first. Oops.

I am now thinking that I should have used ddclient instead. https://docs.linuxserver.io/images/docker-ddclient

Google is doing their usual thing of shutting down perfectly good products and services that were making them money for no reason. Google Domains is transferring to Squarespace and Squarespace doesn't support Dynamic DNS, so I don't want them.
Instead, I switched to Cloudflare as my registrar and had this installed and working before I realized it is no longer developed. Please post if you know of a more recent utility for Cloudflare DDNS, especially if it is nice enough to just be a Docker install that just works.

@BenMcLean https://github.com/domingues/docker-ddclient

@BenMcLean https://github.com/domingues/docker-ddclient

Thanks.