update-dns-record.sh

#!/bin/bash
#
# Updates type "A" record for a subdomain with current external IP Address at Cloudflare.
# Obtain API Token at https://dash.cloudflare.com/profile/api-tokens with permissions "Zone.DNS".
#
# Author: moh@yutsuku.net
# Revision: 2021-09-16
#
# Requires: curl, jq, dig
#

# config start
DOMAIN='example.com'
SUBDOMAIN='home.example.com'
TOKEN='<READ DESCRIPTION>'
# config end

# obtain current external ip address
IP=$(dig +short myip.opendns.com @resolver1.opendns.com)

# get id for main domain (zone)
ZONEID=$(curl -s -X GET "https://api.cloudflare.com/client/v4/zones?name=$DOMAIN" \
     -H "Authorization: Bearer $TOKEN" \
     -H "Content-Type:application/json" | jq -r '.result[].id')

# get id for subdomain (inside zone)
DNS_RECORD=$(curl -s -X GET "https://api.cloudflare.com/client/v4/zones/$ZONEID/dns_records?type=A&name=$SUBDOMAIN" \
     -H "Authorization: Bearer $TOKEN" \
     -H "Content-Type: application/json")
DNS_RECORD_ID=$(echo $DNS_RECORD | jq -r '.result[].id')
DNS_RECORD_CONTENT=$(echo $DNS_RECORD | jq -r '.result[].content')

if [[ $DNS_RECORD_CONTENT = $IP ]]; then
    echo OK
else
    echo UPDATING "A" record for $SUBDOMAIN - $DNS_RECORD_CONTENT to $IP
    # update DNS info
    STATUS=$(curl -s -X PATCH "https://api.cloudflare.com/client/v4/zones/$ZONEID/dns_records/$DNS_RECORD_ID" \
         -H "Authorization: Bearer $TOKEN" \
         -H "Content-Type: application/json" \
         --data "{\"type\":\"A\",\"name\":\"$SUBDOMAIN\",\"content\":\"$IP\"}")
    STATUS_SUCCESS=$(echo $STATUS | jq -r '.success')
    if [[ $STATUS_SUCCESS = "true" ]]; then
        echo OK
    else
        echo FAIL
    fi
fi