Simple dynamic DNS script for OpenWRT using Dreamhost API

dreamhost.sh

#!/bin/sh

# Simplified script for using Dreamhost as a dynamic DNS provider.
# Works on openwrt, but must have ssl support.
# You will probably need to install libustream-openssl and ca-certificates.
# You may need to edit IP detection lines for your specific configuration.
# You could use cron to schedule it to run hourly:
# crontab -e
# 0 * * * * /root/dreamhost.sh
# Don't forget to enable cron!
# /etc/init.d/cron enable
# /etc/init.d/cron start

## Beginning of Configuration ##

# Dreamhost API key.
# Must have permission for dns-list_recort, dns-remove_record, and dns-add_record.
KEY=XXXXXXXXXXXXXXXX

# Record you want to update.
RECORD="hostname.mydomain.com"

# WAN interface from which to obtain public IP addresses.
IFACE="eth0.2"

## End of Configuration ##

# Function for updating Dreamhost record with new IP address $ADDR.
update_record()
{
    # Type of record, A for IPV4 or AAAA for IPV6.
    TYPE=$1
    
    # Query Dreamhost to see if there is an existing record.
    unset NO_CREATE
    unset OLD_ADDR
    OLD_ADDR=`wget -O- -q https://api.dreamhost.com/ --post-data key=$KEY\&unique_id=$(uuidgen)\&cmd=dns-list_records\&type=$TYPE\&editable=1 | egrep "${RECORD}\s+${TYPE}\s+" | egrep -o "([0-9]{1,3}\.){3}[0-9]{1,3}|([0-9a-fA-F]{0,4}:){1,7}([0-9a-fA-F]){0,4}" | awk '{print toupper($0)}'`
    if [ -n "$OLD_ADDR" ]
    then
        # Is our corrent IP address different from the existing record?
        if [ "${ADDR}" = "${OLD_ADDR}" ]
        then
	    # Do not update the record.
            echo "Type $TYPE record for $ADDR is already up to date."
            NO_CREATE=1
        else
	    # There is no "update" API.
            # Must remove old record before creating new one.
            echo "Removing old type $TYPE record for $OLD_ADDR"
            wget -O- -q https://api.dreamhost.com/ --post-data key=$KEY\&unique_id=$(uuidgen)\&cmd=dns-remove_record\&record=$RECORD\&type=$TYPE\&value=$OLD_ADDR
        fi
    fi
    if [ -z "$NO_CREATE" ]
    then
        # Create a new record unless the old record was already up to date.
        echo "Creating new type $TYPE record for $ADDR"
        wget -O- -q https://api.dreamhost.com/ --post-data key=$KEY\&unique_id=$(uuidgen)\&cmd=dns-add_record\&record=$RECORD\&type=$TYPE\&value=$ADDR
    fi
}

# Look up public IP4 address and update A record.
ADDR=`ip -4 addr show dev $IFACE | egrep inet | egrep -o "([0-9]{1,3}\.){3}[0-9]{1,3}" | head -n 1`
update_record A

# Look up public IP6 address and update AAAA record.
# Note that this address might not match the old record exactly because one of
# Dreamhost or ip might use a compressed address format while the other uses
# an expanded format.  In the worst case this will lead to an unneeded address
# update, which is honestly not that big of a deal.
ADDR=`ip -6 addr show dev $IFACE | egrep "inet6.+global" | egrep -o "([0-9a-fA-F]{0,4}:){1,7}([0-9a-fA-F]){0,4}" | awk '{print toupper($0)}'`
update_record AAAA