A bash script to update a Cloudflare DNS A record with the external IP of the source machine

cloudflare-ddns-update.sh

#!/bin/bash

ZONE=domain.com
DNSRECORD=sub.domain.com
TOKEN=<token>

# Get the current external IP address
IP=$(curl -s -X GET https://checkip.amazonaws.com)

CURRENTDATE=`date`
echo $CURRENTDATE
echo "Current IP is $IP"

if host $DNSRECORD 1.1.1.1 | grep "has address" | grep "$IP"; then
  echo "No update required"
  exit
fi

# If here, the DNS A record needs updating

# Get the zone id for the requested zone
ZONEID=$(curl -s -X GET "https://api.cloudflare.com/client/v4/zones?name=$ZONE&status=active" \
    -H "Authorization: Bearer $TOKEN" \
    -H "Content-Type: application/json" | jq -r '{"result"}[] | .[0] | .id')

echo "Zoneid for $ZONE is $ZONEID"

# Get the DNS record id
DNSRECORDID=$(curl -s -X GET "https://api.cloudflare.com/client/v4/zones/$ZONEID/dns_records?type=A&name=$DNSRECORD" \
    -H "Authorization: Bearer $TOKEN" \
    -H "Content-Type: application/json" | jq -r '{"result"}[] | .[0] | .id')

echo "DNS record ID for $DNSRECORD is $DNSRECORDID"

# Update the record
curl -s -X PUT "https://api.cloudflare.com/client/v4/zones/$ZONEID/dns_records/$DNSRECORDID" \
    -H "Authorization: Bearer $TOKEN" \
    -H "Content-Type: application/json" \
    --data "{\"type\":\"A\",\"name\":\"$DNSRECORD\",\"content\":\"$IP\",\"ttl\":1,\"proxied\":false}" | jq