Simple bash script to update Cloudflare DNS record to represent local public IP i.e. DDNS script

cloudflare_ddns.sh

#!/bin/bash

####################################################################################
# Author: Kernelkaribou@github
#
# Purpose: Update a DNS record hosted at Cloudflare to represent network public IP. 
# Based upon Cloudflare API v4
#
# In cloudflare, create API key for your zone in question, e.g. example.com
# Ensuring that it has Zone Read and DNS Edit permissions. DO NOT use a Global Key
# for your account as that is unnecessarily permissive.
#
# Fill in the below user defined variables and set up a cron to run on a necessary interval
# e.g. every hour, 5 minutes, day, etc.
#
# When ran manually it will output results to the screen but will also write to syslog 
# for unattended runs and historic review.
#
# Last Update: 03/05/2023
####################################################################################

### User Defined

#Main domain zone e.g. example.com
ZONE_DOMAIN="EXAMPLE.COM" 
#DNS Record to update e.g. home.example.com
DNS_RECORD="RECORD.EXAMPLE.COM" 
#API Key generated with Zone Read and DNS Edit permissions on above Main Zone, NOT A GLOBAL KEY!
API_KEY="CLOUDFLAREAPIKEY" 

#Send message of execution to log center on Synology
writeLog()
{
    echo $2
	logger "Cloudflare DDNS: ${2}"
}

### Main Script

#Get my public IP address
PUBLIC_IP=$(curl -s ifconfig.me)

#Get current DNS Record configured IP from Cloudflare
CURRENT_DNS_IP=$(nslookup -type=a $DNS_RECORD 1.1.1.1 | grep 'Address' | awk -F":" 'NF==2' | awk '{ if($2 !~ /#/){print $2}}')

#CHECK IF DNS Record matches Public IP
if [[ $CURRENT_DNS_IP == $PUBLIC_IP ]]; then
	
    #IP Matches no need to continue
    MESSAGE="$DNS_RECORD IP: $CURRENT_DNS_IP, Public IP: $PUBLIC_IP Match! No DNS update necessary!"
    MESSAGE_TYPE="info"
    writeLog "$MESSAGE_TYPE" "$MESSAGE"

else

	MESSAGE="$DNS_RECORD IP $CURRENT_DNS_IP, Public IP: $PUBLIC_IP Mismatch! Updating!"
	MESSAGE_TYPE="info"
    writeLog "$MESSAGE_TYPE" "$MESSAGE"
	

	#Getting Domain Zone ID
	ZONE_RESULT=$(curl -s -X GET "https://api.cloudflare.com/client/v4/zones?name=$ZONE_DOMAIN" \
	-H "Authorization: Bearer $API_KEY" \
	-H "Content-Type: application/json")
	ZONE_ID=$(echo $ZONE_RESULT | grep -oP "(?<={\"result\":\[{\"id\":\").*?(?=\",)")
	
	echo "ZONE ID: $ZONE_ID"
	
    if [ -z "$ZONE_ID" ]; then
		
		MESSAGE="Unable to get ID for Zone '$ZONE_DOMAIN', check script configuration and API key"
		MESSAGE_TYPE="err"

        writeLog "$MESSAGE_TYPE" "$MESSAGE"
        echo $ZONE_RESULT
        exit 1

    fi

	#Getting DNS Record ID
	RECORD_RESULT=$(curl -s -X GET "https://api.cloudflare.com/client/v4/zones/$ZONE_ID/dns_records?name=$DNS_RECORD" \
	-H "Authorization: Bearer $API_KEY" \
	-H "Content-Type: application/json")
	DNS_ID=$(echo $RECORD_RESULT | grep -oP "(?<={\"result\":\[{\"id\":\").*?(?=\",)")
	
	echo "DNS RECORD ID: $DNS_ID"
	
    if [ -z "$DNS_ID" ]; then

		MESSAGE="Unable to get ID for DNS Record '$DNS_RECORD', check script configuration and Zone ID"
		MESSAGE_TYPE="err"

        writeLog "$MESSAGE_TYPE" "$MESSAGE"
        echo $RECORD_RESULT
        exit 1

    fi
    
    #Updating DNS record.
	RESPONSE=$(curl -s -X PUT https://api.cloudflare.com/client/v4/zones/$ZONE_ID/dns_records/$DNS_ID \
	           -H "Content-Type: application/json" \
	           -H "Authorization: Bearer $API_KEY" \
	           -H "cache-control: no-cache" \
	           -d "{\"type\" : \"A\", \"name\" : \"$DNS_RECORD\", \"content\" : \"$PUBLIC_IP\" }")
	
	#Update failed
   	ERROR_STRING='"success":false,'
	if [[ "$RESPONSE" == *"$ERROR_STRING"* ]]; then
	    
	    ERROR_MESSAGE=""
	    if [[ $RESPONSE =~ \"errors\"\:[{.*[A-Za-z0-9].*}\] ]]; then
	        ERROR_MESSAGE=$(echo ${BASH_REMATCH[0]} | sed 's/[^a-z  A-Z:0-9]/ /g')
	    else
	        ERROR_MESSAGE="Unable to parse error message"
	    fi
		
		MESSAGE="DNS Record $DNS_RECORD error on update: $PUBLIC_IP - $ERROR_MESSAGE"
		MESSAGE_TYPE="err"
	
	#Update was successful	
	else
		  
	    MESSAGE="DNS Record $DNS_RECORD successfully updated to $PUBLIC_IP"
   	    MESSAGE_TYPE="info"
	    NOTIFICATION="$DNS_RECORD was successfully updated to $PUBLIC_IP"

	fi

    writeLog "$MESSAGE_TYPE" "$MESSAGE"

fi