Simple script to refresh a DNSimple zone record from an LEDE wan IP, for dynsns behaviour with DNSimple

update_dnsimple_host.sh

#!/bin/sh

###############
# User Variables, These MUST be set
###############

# Credentials
# Be sure that if there are restricted characters like " in the password that they are escaped, eg, ="A\"B"
# TODO: storing in a built in encrypted location, to prevent accidental copy including credentials.
DNSimpleUser="yourusername@yourdomain.com"
DNSimplePassword="yourpassword"

# The zone record path.  This should be the form of {accountid}/zones/{domain name}/records/{record id}
# and can be easily retrieved by logging into dnsimple web interface and editing the record, the url
# will contain all this information in this same format.
DNSimpleZoneApiPath="12345/zones/mysuperdomain.com/records/12345678"


##########
# Constants for the script
##########
DNSimpleApiBase="https://api.dnsimple.com/v2"

########
# Get the lede wan ip address.
########
wan_ip=`ubus call network.interface.wan status |
        grep \"address\" |
        grep -oE '([0-9]{1,3}\.){3}[0-9]{1,3}';`
echo Retrieved Wan Ip: $wan_ip

########
# Check the dnsimple host entry.
########
dns_ip=`curl \
        -silent \
        -u $DNSimpleUser:$DNSimplePassword \
        -H 'Content-Type: application/json' \
        $DNSimpleApiBase/$DNSimpleZoneApiPath 2>&1 |
        grep -oE \"content\":\"[0-9.]*\" |
        grep -oE '([0-9]{1,3}\.){3}[0-9]{1,3}';`
echo Retrieved DNS Ip: $dns_ip

########
# If it is different, update it to wan ip
########
if [ $dns_ip != $wan_ip ]; then
        echo DNS entry differs, updating dns to wan ip..
        updated_ip=`curl \
                -silent \
                -u $DNSimpleUser:$DNSimplePassword \
                -X PATCH \
                -H 'Content-Type: application/json' \
                --data '{"content": "'$wan_ip'"}' \
                $DNSimpleApiBase/$DNSimpleZoneApiPath |
                grep -oE \"content\":\"[0-9.]*\" |
                grep -oE '([0-9]{1,3}\.){3}[0-9]{1,3}';`
        echo $updated_ip
        if [ $updated_ip = $wan_ip ]; then
                echo DNS entry updated. Everything is Awesome!
        else
                echo Couldn\'t update DNS Zone.
                # TODO: fail like a shell script should. log? email?
        fi
else
        echo DNS already up to date, nothing to do.
fi

Simple script to update DNSimple host record file. To use it, modify the parameters at the top, copy it into a file (I put it in /usr/bin/update_dnsimple_host.sh) then chmod u+x and run it. Feedback from experienced script authors welcome.. I'm not a linux guy (yet :) )