Here's what Jeff Siddall I've found so far:
# The device id (did) is 18 decimal digits long
# on is a 1
# off is a 0
# the %dim is between 1 to 100 (can be set when off and it will turn on to that level).
#
# For on or off
cmd="cmd=DeviceSendCommand&data=%3Cgip%3E%3Cversion%3E1%3C%2Fversion%3E%3Ctoken%3E1234567890%3C%2Ftoken%3E%3Cdid%3E
${DeviceID}%3C%2Fdid%3E%3Cvalue%3E
${DeviceCmd}%3C%2Fvalue%3E%3C%2Fgip%3E&fmt=xml"
# For %dim DeviceCmd is the %
cmd="cmd=DeviceSendCommand&data=%3Cgip%3E%3Cversion%3E1%3C%2Fversion%3E%3Ctoken%3E1234567890%3C%2Ftoken%3E%3Cdid%3E
${DeviceID}%3C%2Fdid%3E%3Cvalue%3E
${DeviceCmd}%3C%2Fvalue%3E%3Ctype%3Elevel%3C%2Ftype%3E%3C%2Fgip%3E&fmt=xml"
echo -n "${cmd} | POST -c 'application/x-www-form-urlencoded; charset=UTF-8'
http://tcp.uucp/gwr/gop.php
If it worked you'll get back:
<gip><version>1</version><rc>200</rc></gip>
If not (not sure it's the only value):
<gip><version>1</version><rc>500</rc></gip>