A bash script to update a dynamic DNS entry on Google Domain using their provided API.

gyndns

#!/bin/bash
# 
# Copyright 2015-present Patrice Jaton.
# 
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
# 
# http://www.apache.org/licenses/LICENSE-2.0
# 
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
# 
# 
# Script using Google's domain API to update a Dynamic DNS entry
# see https://support.google.com/domains/answer/6147083?hl=en
# 

username=
password=
agent=
ip=
offline=
verbose=

function usage() { 
    script=`basename $0`
    echo "usage: $script -u username -p password -a agent [-i ipaddress | -o | -f] [-v] hostname";
    echo "       $script -h";
    echo "  -u username   The username associated with the host that is to be updated";
    echo "  -p password   The password associated with the host that is to be updated";
    echo "  -a agent      The required HTTP user-agent requesting the update";
    echo "  -i ipaddress  The optional new IP address. If not specified, the IP of the";
    echo "                agent sending the request will be used";
    echo "  -o            Turn the dynamic hostname online";
    echo "  -f            Turn the dynamic hostname offline";
    echo "  -v            Verbose mode";
    echo "  -h            Display this help"
}

function valid_ip()
{
    local ip=$1
    local stat=1

    if [[ $ip =~ ^[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}$ ]]; then
        OIFS=$IFS
        IFS='.'
        ip=($ip)
        IFS=$OIFS
        [[ ${ip[0]} -le 255 && ${ip[1]} -le 255 \
            && ${ip[2]} -le 255 && ${ip[3]} -le 255 ]]
        stat=$?
    fi
    return $stat
}

if [ $# -eq 0 ] ; then
    usage
    exit 0
fi

options=':u:p:a:i:hofv'
while getopts $options option
do
    case $option in
        u)    username=$OPTARG;;
        p)    password=$OPTARG;;
        a)    agent=$OPTARG;;
        i)    
            if [ -z "$offline" ]; then 
                ip=$OPTARG; 
                if (! valid_ip $ip); then
                    echo "\"$ip\" is not a valid IPv4 address"
                    exit 1
                fi;
            else 
                echo "-i, -o and -f cannot be used together" >&2
                usage >&2
                exit 1
            fi;;
        o)    
            if [ -z "$offline" ] && [ -z "$ip" ]; then 
                offline=false
            else 
                echo "-i, -o and -f cannot be used together" >&2
                usage >&2
                exit 1
            fi;;
        f)    
            if [ -z "$offline" ] && [ -z "$ip" ]; then 
                offline=true
            else 
                echo "-i, -o and -f cannot be used together" >&2
                usage >&2
                exit 1
            fi;;
        v)    verbose="-v";;
        h)    usage; exit;;
        \?)   echo "unknown option: -$OPTARG" >&2; usage >&2; exit 1;;
        :)    echo "missing argument for option: -$OPTARG" >&2; usage >&2; exit 1;;
        *)    echo "unimplemented option: -$option" >&2; usage >&2; exit 1;;
    esac
done

missings=()
for argument_name in 'username' 'password' 'agent'
do
    eval argument_value=\$$argument_name
    if [ -z "$argument_value" ]; then
        missings+=($argument_name)
    fi
done

shift $(($OPTIND - 1))
if [ $# -eq 0 ] ; then
    missings+=("hostname")
elif [ ! $# -eq 1 ] ; then
    echo "too many arguments" >&2
    usage >&2
    exit 1
else
    hostname=$1
fi
if [ ! ${#missings[@]} -eq 0 ]; then
    echo "missing: ${missings[*]}" >&2
    usage >&2
    exit 1
fi

queryString="hostname=$hostname"
if [ -n "$ip" ]; then
    queryString+="&myip=$ip" 
fi
if [ -n "$offline" ]; then
    if ($offline); then
        queryString+="&offline=yes"
    else
        queryString+="&offline=no"
    fi 
fi

status=`curl -s $verbose -H "User-Agent: $agent" --user $username:$password https://domains.google.com/nic/update?$queryString >&1`
case $status in
    nohost)   echo "The hostname \"$hostname\" does not exist, or does not have Dynamic DNS enabled." >&2; exit 1;;
    badauth)  echo "The username / password combination is not valid for the specified host." >&2; exit 1;;
    notfqdn)  echo "The supplied hostname \"$hostname\" is not a valid fully-qualified domain name." >&2; exit 1;;
    badagent) 
        if [ -n "$ip"]; then
            echo "Either the agent \"$agent\" is invalid or the IP address \"$ip\" is not a valid IPv4 address." >&2
            exit 1
        else
            echo "The agent \"$agent\" is invalid." >&2
            exit 1
        fi;;
    abuse)    echo "Dynamic DNS access for the hostname has been blocked due to failure to interpret previous responses correctly." >&2; exit 1;;
    911)      echo "An error happened on our end. Wait 5 minutes and retry." >&2; exit 1;;
    good*)
        if [ ! -z "$offline" ]; then
            if ($offline); then
                echo "The dynamic DNS for \"$hostname\" is now offline."
            else
                echo "The dynamic DNS for \"$hostname\" is back online and set to ${status#good }."
            fi 
        else
            echo "The dynamic DNS for \"$hostname\" is now set to ${status#good }."
        fi;;
    nochg*)
        if [ ! -z "$offline" ]; then
            if ($offline); then
                echo "The dynamic DNS for \"$hostname\" was not change and remains offline."
            else
                echo "The dynamic DNS for \"$hostname\" was not change and remains online set to ${status#nochg }."
            fi 
        else
            echo "The dynamic DNS for \"$hostname\" was not changed and remains set to ${status#nochg }."
        fi;;
    *)        echo "Unexpected response \"$status\" from the server!"; exit 1;;
esac