#!/bin/sh
BACKLIGHT_MASTR=/sys/class/backlight/acpi_video0
BACKLIGHT_SLAVE=/sys/class/backlight/intel_backlight

update()
{
	# Read current values
	local mastr_val="`cat "${BACKLIGHT_MASTR}/brightness"`"
	local mastr_max="`cat "${BACKLIGHT_MASTR}/max_brightness"`"
	local slave_max="`cat "${BACKLIGHT_SLAVE}/max_brightness"`"
	
	# Calculate new slave brightness value
	local slave_val=$((${mastr_val}*${slave_max}/${mastr_max}))
	
	if [ ${slave_val} -lt 1 ];
	then
		slave_val=1
	fi
	
	# Set new slave value
	echo "${slave_val}" >"${BACKLIGHT_SLAVE}/brightness"
}

while true;
do
	# Adjust backlight
	update

	# Wait for next brightness change
	inotifywait --quiet --quiet --event modify "${BACKLIGHT_MASTR}/brightness"
done