:local username "<dyn.com user name>"
:local password "<dyn.com password or, better, Updater Client Key>"
:local hostname "<dyn.com host name>"
:local emailAddress "<where to send notifications>"

:local url "dummy"
:local previousIP

:global dyndnsForce

:set dyndnsForce false

:log info ("UpdateDynDNS starts.")

# print some debug info
#:log info ("UpdateDynDNS: username = $username")
#:log info ("UpdateDynDNS: password = $password")
#:log info ("UpdateDynDNS: hostname = $hostname")
#:log info ("UpdateDynDNS: previousIP = $previousIP")

# I have some doubt over the persistence of the global previousIP.
# This value should be stored in /dyndns.txt after the last update attempt,
# preceded by the status and a space.
# For status values see: https://help.dyn.com/remote-access-api/return-codes/

:if ([:len [/file find name=dyndns.txt]] > 0) do={
   :local ipfile [/file get dyndns.txt contents]
   :local ipstart ([find $ipfile " " -1] + 1)
   :local ipend [:len $ipfile]
   :set previousIP [:pick $ipfile $ipstart $ipend]
} else={
   :set previousIP "0.0.0.0"
}

# get the current IP address from the internet (in case of double-nat)
/tool fetch mode=http address="checkip.dyn.com" src-path="/" dst-path="/dyndns.checkip.html"
:delay 1
:local result [/file get dyndns.checkip.html contents]

# parse the current IP result
:local resultLen [:len $result]
:local startLoc [:find $result ": " -1]
:set startLoc ($startLoc + 2)
:local endLoc [:find $result "</body>" -1]
:local currentIP [:pick $result $startLoc $endLoc]

# Remove the # on next line to force an update every single time - useful for debugging,
# but you could end up getting blacklisted by DynDNS!

#:set dyndnsForce true

# Determine if dyndns update is needed
# more dyndns updater request details http://www.dyndns.com/developers/specs/syntax.html

:if (($currentIP != $previousIP) || ($dyndnsForce = true)) do={
   :log info ("Changing IP from $previousIP to $currentIP.")
   :set dyndnsForce false
   :set url "http://$username:$password@members.dyndns.org/nic/update?hostname=$hostname&myip=$currentIP&wildcard=no"
   /tool fetch url=$url mode=http dst-path="/dyndns.txt"

# Original code:
#   /tool fetch user=$username password=$password mode=http address="members.dyndns.org" \
#      src-path="nic/update?system=dyndns&hostname=$hostname&myip=$currentIP&wildcard=no" \
#      dst-path="/dyndns.txt"

   :delay 1

#  :set previousIP $currentIP

   :local result [/file get dyndns.txt contents]
   :log info ("UpdateDynDNS: Dyndns update needed")
   :log info ("UpdateDynDNS: Dyndns Update Result: ".$result)

# email result:
   :local output "DynDNS Update Result: $result"
   /tool e-mail send to="$emailAddress" subject="DynDNS update $currentTime" body="$output"
} else={
   :log info ("UpdateDynDNS: No dyndns update needed")
}