[vbat99]

A while ago I found a simpler fix for this issue. Please note, this is not my code, I can't find the original post, but it works.

Basically, If a connection is sensed on VGA output, it switches the laptop LCD off.

create a file in /etc/X11/Xsession.d called 45custom_randr-settings
and enter the following:

EXTERNAL_OUTPUT="VGA1"
INTERNAL_OUTPUT="LVDS1"

xrandr |grep $EXTERNAL_OUTPUT | grep " connected "
if [ $? -eq 0 ]; then
xrandr --output $INTERNAL_OUTPUT --off --output $EXTERNAL_OUTPUT --auto
else
xrandr --output $INTERNAL_OUTPUT --auto --output $EXTERNAL_OUTPUT --off
fi

now you'll note the first two lines pick the internal or external ports,
so by doing

xrandr -d :0 -q

first, you can pick which ports you want to set.

You should be able to set it for VGA1 or DVI1 and external output.

Hope this helps someone.