A DDNS Bash script to refresh DNSPod.cn record according to always changing public IP.

ddns.sh

#!/bin/bash

validateIp() {
        oldIFS=$IFS
        IFS=.
        set -- $1
        IFS=${oldIFS}

        # Ensure there are 4 parts.
        [[ "$#" -ne "4" ]] && exit 1

        for oct in $1 $2 $3 $4; do
                # Ensure \'${oct}\' is not NaN.
                [[ ${oct} =~ ^[0-9]+$ ]] || exit 1

                # Ensure \'${oct}\' is within [0, 255].
                [[ "${oct}" -lt "0" || "${oct}" -gt "255" ]] && exit 1
        done
}

source ~/.ddns

echo Retrieving current IP...
currentIp=$(curl -s ${IP_SERVICE})
if [ "$?" -ne "0" ]; then
        echo Something wrong when retrieving dynamic IP. Exiting now and will try again later.
        exit 1
fi

echo Current IP is ${currentIp}.
validateIp ${currentIp}
declare lastIp
if [ -f ${LOG_PATH} ]; then
        echo Retrieving last IP from log...
        lastIp=$(tail -1 ${LOG_PATH}|awk '{print $2}')
else
        echo Retrieving last IP from DNS record...
#       lastIp=$(host ${SUB_DOMAIN}.${DOMAIN}|awk '{print $4}')
fi

echo Last IP record is ${lastIp}.

[ "${currentIp}" == "${lastIp}" ] && echo IP unchanged. && exit 0

echo Updating DDNS record...
# curl -X POST https://dnsapi.cn/Record.Ddns -d "login_token=${LOGIN_ID},${LOGIN_TOKEN}&format=json&domain_id=${DOMAIN_ID}&record_id=${RECORD}&record_line=默认&sub_domain=${SUB_DOMAIN}"

echo Saving to log...
if [ "$?" -eq "0" ];then
        currentTime=$(date -Ins)
        echo "${currentTime} ${currentIp}" >> ${LOG_PATH}
else
        echo Error occurred.
fi