Bash Script to Update Cloudflare DNS Record upon IP Address Change

ddns.sh

#!/bin/bash

# This script by NKID00 is marked CC0 1.0.

set -e

# To query dns record id:
# curl https://api.cloudflare.com/client/v4/zones/$ZONE_ID/dns_records \
#   -H "Authorization: Bearer $API_TOKEN"

ZONE_ID=1
DNS_RECORD_ID=2
API_TOKEN=3
DOMAIN=4
DEVICE=5

function query_ip_address() {
  addr="$(
    ip -6 -j addr show dev $DEVICE scope global primary -tentative up \
      | jq -r '(.[0] // empty).addr_info | sort_by(.prefixlen) | map(.local // empty)[0] // empty'
  )"
  if [ -z "$addr" -o "$addr" = "$previous" ]; then
    return 1
  fi
  previous="$addr"
  return 0
}

function update_record() {
  printf -- "IP addr is now [$addr], updating... "
  comment="Updated on $(date -Is)"
  export DOMAIN addr comment
  jq -n '{name: env.DOMAIN, content: env.addr, comment: env.comment, ttl: 60, type: "AAAA", proxied: false}' \
    | curl https://api.cloudflare.com/client/v4/zones/$ZONE_ID/dns_records/$DNS_RECORD_ID \
      -s -X PUT -H "Authorization: Bearer $API_TOKEN" --json @- \
    | jq -r 'if .success then "OK" else ("Error", .) end'
}

query_ip_address && update_record
ip -6 mon addr dev $DEVICE | while true; do
  read -r -t 3600  # Force recheck after timeout
  query_ip_address && update_record
done