check-monitors

#!/bin/sh

# Check monitors and use xrandr to turn on the appropriate one(s).

# Ideally, this would be run from /etc/pm/sleep.d/check-monitors
# upon resume from suspend., something like this:
# case "${1}" in
#     resume|thaw)
#         check-monitors
#         ;;
# esac
# Unfortunately, /etc/pm/sleep.d/check-monitors isn't called reliably
# on resume, and neither is any other script. So it might be best
# to bind this to a key so that if you dock your laptop then wake it up,
# you can call it with a function key even if you can't see the screen
# to put focus in a window.
#
# This leaves debugging info in /tmp/check-monitors
# because if it fails, you won't be able to see any error output
# but maybe you can shell in and read what happened.

DEBUGFILE=/tmp/check-monitors

date >>$DEBUGFILE

getmonitor() {
    xrandr | grep $1 | sed 's/ .*$//'
}

# Check whether an HDMI monitor is connected: returns 0 on success
xrandr | grep HDMI | grep " connected " >>$DEBUGFILE 2>&1
if [ $? -eq 0 ]; then
    echo "==== Choosing HDMI" >>$DEBUGFILE
    xrandr --output $(getmonitor LVDS) --off
    xrandr --output $(getmonitor VGA) --off
    xrandr --output $(getmonitor HDMI) --auto
else
    xrandr | grep VGA | grep " connected " >>$DEBUGFILE
    if [ $? -eq 0 ]; then
        echo "==== Choosing VGA" >>$DEBUGFILE 2>&1
        xrandr --output $(getmonitor HDMI) --off
        xrandr --output $(getmonitor LVDS) --off
        xrandr --output $(getmonitor VGA) --auto
    else
        # Fall back on the built-in laptop display, LVDS1
        echo "==== Choosing built-in display" >>$DEBUGFILE
        xrandr --output $(getmonitor VGA) --off
        xrandr --output $(getmonitor HDMI) --off
        xrandr --output $(getmonitor LVDS) --auto
    fi
fi

xrandr >>$DEBUGFILE
echo "=====" >>$DEBUGFILE