Linode dynamic DNS updating script

update-dns.sh

#!/bin/bash
# Modified by Chris Richardson (https://github.com/christr and https://twitter.com/christr77) on 09/20/2020
# Previous versions of this script don't work because they hadn't been updated since 2012. There are now more steps involved to set this up.

# This script update is based on information found here: https://developers.linode.com/api/v4/domains-domain-id-records-record-id/#put

# You first must find out the domain ID and resource ID numbers. In order to do this follow the steps below.
# 1. Create a Linode API Key through your account profile at https://cloud.linode.com/dashboard. Give it rights to read/write to domains only.
# 2. From a shell run the following command: LINODE_API_KEY=[insert API key from step 1 here]
# 3. Run the following command to get the domain ID number for the domain you want to manage: curl -H "Authorization: Bearer $LINODE_API_KEY" https://api.linode.com/v4/domains/
# 4. From a shell run the following command: DOMAIN_ID=[insert domain ID number from step 3 here]
# 5. Run the following command to get the resource ID number for the subdomain you want to manage: curl -H "Authorization: Bearer $LINODE_API_KEY" https://api.linode.com/v4/domains/$DOMAIN_ID/records/
# 6. From a shell run the following command: RESOURCE_ID=[insert resource ID number from step 5 here]
# 7. Run the following command to verify the current settings for this resource: curl -H "Authorization: Bearer $LINODE_API_KEY" https://api.linode.com/v4/domains/$DOMAIN_ID/records/$RESOURCE_ID
# 8. Use the information collected from these commands to complete the variables below in this script.

LINODE_API_KEY=
DOMAIN_ID=
RESOURCE_ID=
NAME=

function resource_update {
curl -H "Content-Type: application/json" \
	-H "Authorization: Bearer $LINODE_API_KEY" \
	-X PUT -d '{
		"type": "A",
		"name": "'$NAME'",
		"target": "'$WAN_IP'",
		"priority": 0,
		"weight": 0,
		"port": 0,
		"service": null,
		"protocol": null,
		"ttl_sec": 0,
		"tag": null
	}' \
	https://api.linode.com/v4/domains/$DOMAIN_ID/records/$RESOURCE_ID
}

WAN_IP=`curl -s ifconfig.me/ip`
if [ -f $HOME/.wan_ip.txt ]; then
	OLD_WAN_IP=`cat $HOME/.wan_ip.txt`
else
	echo "No file, need IP"
	OLD_WAN_IP=""
fi

if [ "$WAN_IP" = "$OLD_WAN_IP" ]; then
	echo "IP Unchanged"
else
	echo $WAN_IP > $HOME/.wan_ip.txt
	echo "Updating DNS to $WAN_IP. Results from Linode are displayed below."
	resource_update
fi