cloudflare-ddns.sh

#!/bin/bash

CF_TOKEN="Gh_0000000000000000000000000000000000000"  # generated API token with DNS edit on your zone ID
CF_ZONE_ID="00000000000000000000000000000000"        # the zone ID found in the Overview tab
CF_RECORD="dynamic.example.domain"                   # your record within the zone you want to update

# SCRIPT BELOW - DON'T EDIT

RESET=$(tput sgr0)
DATE_ANSI=$(tput setaf 4)
HEADER_ANSI="$(tput setaf 6)$(tput bold)"
ERROR_ANSI="$(tput setab 1)$(tput setaf 7)$(tput bold)"

log() {
    echo "${DATE_ANSI}[`date -u`]${RESET}" "${HEADER_ANSI}[CloudFlare DDNS]${RESET} $@"
}

log_error() {
    log "${ERROR_ANSI}[$1]${RESET}" "${@:2}"
}

if ! command -v jq &> /dev/null; then
  log_error "Error" "jq is not installed."
  exit 1
fi

if ! command -v curl &> /dev/null; then
  log_error "Error" "curl is not installed."
  exit 1
fi

api() {
    local result;
    result=$(curl -s -X $1 \
        -H "Authorization: Bearer $CF_TOKEN" \
        -H "Content-Type: application/json" \
        --data "$3" \
        "https://api.cloudflare.com/client/v4/zones/$CF_ZONE_ID/dns_records$2")
    if [[ "$?" != "0" ]]; then
        log_error "CURL Error" "Returned non-zero. Check your WAN connectivity."
        exit 1
    fi
    if [[ $(echo "$result" | jq -r '.success') == "false" ]]; then
        log_error "CloudFlare Error" "CloudFlare call did not succeed. Check credentials."
        exit 1
    fi
    echo "$result"
}

UPDATES=false
IPV4=$(dig -4 TXT +short o-o.myaddr.l.google.com @ns1.google.com | awk -F'"' '{ print $2 }')
IPV6=$(dig -6 TXT +short o-o.myaddr.l.google.com @ns1.google.com | awk -F'"' '{ print $2 }')

RESULT=$(api GET "?name=$CF_RECORD")
if [[ "$?" != "0" ]]; then
    echo "$RESULT"
    exit 1
fi

RECORD_IPV4=$(echo "$RESULT" | jq -r '.result[] | select(.type == "A") | .content')
RECORD_IPV4_ID=$(echo "$RESULT" | jq -r '.result[] | select(.type == "A") | .id')

if [[ "$RECORD_IPV4_ID" == "" ]]; then
    log "Warning: No A record found for $CF_RECORD. Skipped A update."
elif [[ "$RECORD_IPV4" != "$IPV4" ]]; then
    IPV4_RESULT=$(api PUT "/$RECORD_IPV4_ID" "{\"id\":\"$RECORD_IPV4_ID\",\"type\":\"A\",\"proxied\":false,\"name\":\"$CF_RECORD\",\"content\":\"$IPV4\"}")
    if [[ "$?" != "0" ]]; then
        echo "$RESULT"
        exit 1
    fi
    UPDATES=true
    log "Updated A $CF_RECORD to $IPV4"
fi

RECORD_IPV6=$(echo "$RESULT" | jq -r '.result[] | select(.type == "AAAA") | .content')
RECORD_IPV6_ID=$(echo "$RESULT" | jq -r '.result[] | select(.type == "AAAA") | .id')

if [[ "$RECORD_IPV6_ID" == "" ]]; then
    log "Warning: No AAAA record found for $CF_RECORD. Skipped AAAA update."
elif [[ "$RECORD_IPV6" != "$IPV6" ]]; then
    IPV6_RESULT=$(api PUT "/$RECORD_IPV6_ID" "{\"id\":\"$RECORD_IPV6_ID\",\"type\":\"AAAA\",\"proxied\":false,\"name\":\"$CF_RECORD\",\"content\":\"$IPV6\"}")
    if [[ "$?" != "0" ]]; then
        echo "$RESULT"
        exit 1
    fi
    UPDATES=true
    log "Updated AAAA $CF_RECORD to $IPV6"
fi

if [[ "$UPDATES" == "false" ]]; then
    log "No updates needed."
fi

I have it installed as a crontab in my $HOME/bin folder. My crontab looks like this:

TERM=xterm
*/5 * * * * $HOME/bin/cloudflare-ddns.sh >>$HOME/bin/.cloudflare-ddns.log 2>&1

Keep in mind because I'm using tput in the script to make it fancy you should set the TERM=xterm in either the script or the crontab. You could also change the formatting lines (at the top) to remove the tput reliance.