afraid.org DDNS updater

ddns-update.sh

#/bin/bash

# Cron every 10 minutes:
# 0,10,20,30,40,50 * * * * /usr/local/sbin/ddns-update
#
# For logging:
# $ mkdir /var/log/ddns-update
# $ cat << EOF > /etc/logrotate.d/ddns-update
# /var/log/ddns-update.log {
#    rotate 3
#    monthly
#    compress
#    missingok
# }
# EOF

PATH='/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin'

basename="$(basename $0)"
serviceURL='http://icanhazip.com'
updateURL='https://freedns.afraid.org/dynamic/update.php?YOUR_SECRET_TOKEN'
database="/etc/default/${basename}"

log="/var/log/${basename}/${basename}.log"
timestamp="$(date --rfc-3339=seconds | tr -d '\n')"

function update_ip() {
    # usage: update_ip "url"
    local url="$1"

    curl --silent "${url}"
    return 0 
}

function update_database() {
    # usage: update_database "file" "ip"
    local file="$1"
    local ip="$2"

    echo "STORED_IP='${ip}'" > "${file}"
    return 0
}

function get_current_ip() {
    # usage: get_current_ip "service"
    local service="$1"
    local response="$(curl --silent ${service})"
    local pattern='^[0-9]+\.[0-9]+\.[0-9]+\.[0-9]+$'

    # set CURRENT_IP global
    if [[ "${response}" =~ $pattern ]]; then
        CURRENT_IP="${response}"
    fi
    return 0
}

# get $STORED_IP
if [[ -f "${database}" ]]; then
    source "${database}"
fi

# get $CURRENT_IP
get_current_ip "${serviceURL}"

# set new IP if it changed
if [[ "${STORED_IP}" != "${CURRENT_IP}" ]]; then
    update_ip "${updateURL}" >> "${timestamp} ${log}"
    update_database "${database}" "${CURRENT_IP}"
fi