GratisDNS.sh

#!/bin/sh

# User Configuration
__USERNAME__=MyUserName
__PASSWORD__=MyPassword
__HOSTNAME__=host.example.com
__DOMAIN__=example.com

# System Configuration
# Set the __INTERFACE__ varible to nothing (__INTERFACE__=) to use external lookup.
__INTERFACE__=eth1
__IP_CACHE__=/tmp/gratisdns_ddns_ip.txt
__LOG__=/var/log/gratisdns_ddns.log

# Get the last known DDNS IP
if [ ! -e ${__IP_CACHE__} ]; then
    touch ${__IP_CACHE__}
fi
__PREVIOUS_IP__=$(cat ${__IP_CACHE__})

# Get the current IP
if [ -z "${__INTERFACE__}" ]; then
    __IP__=$(curl -s "http://automation.whatismyip.com/n09230945.asp")
else
    __IP__=$(ifconfig ${__INTERFACE__} | sed '/inet\ /!d;s/.*r://g;s/\ .*//g')
fi

if [ "${__PREVIOUS_IP__}" == "${__IP__}" ]; then
    # Identical IP's, no change needed
    echo "$(date)   INFO! No change." >> ${__LOG__}
    true;
else
    echo "$(date)   INFO! IP changed. Old: ${__PREVIOUS_IP__}. New: ${__IP__}. Attempting to update DNS." >> ${__LOG__}

    # Update DNS record
    __QUERY_URL__="https://ssl.gratisdns.dk/ddns.phtml?u=${__USERNAME__}&p=${__PASSWORD__}&d=${__DOMAIN__}&h=${__HOSTNAME__}&i=${DDNS_CURRENT_IP}"
    __QUERY_STATUS__=$(curl -s -k "${__QUERY_URL__}")
    if [ "${__QUERY_STATUS__:0:2}" == "OK" ]; then
        # Update IP got OK. Writing new IP to file
        echo ${__IP__} > ${__IP_CACHE__}
        echo "$(date)   INFO! IP successfully updated to ${__IP__}." >> ${__LOG__}
    else
        echo "$(date)   ERROR! Something unexpected happened when trying to update DNS. Status message from server: ${__QUERY_STATUS__}" >> ${__LOG__}
    fi
fi