Can I get a little help with creating a shutdown script?
My observatory is solar-powered and I use a West Mountain Radio RigRunner 4005i intelligent power switch for 12V. It has a simple web-based interface controllable via Ethernet. More info here:

I can connect to its internal webserver and get status. If the voltage gets low, like 11.5v, I want to start shutting things down before I am out of juice.
It has a parsable XML status like this: http://rr4005i/status.xml
<?xml version="1.0"?>

Basically I need to do an http request for the status page, parse out the value of the <supply> voltage, and then kick off a shutdown.

If I get most sophisticated, it would be great to post some values to disable the various output rails to turn off things like dew controller etc.

Pointers and suggestions most welcome.
Thanks in advance