thinkpadbrightness.sh

#!/bin/sh

# /etc/acpi/thinkpadbrightness.sh
# 
# Script to change brightness of a ThinkPad t540p
#
# put this to /etc/acpi/events/thinkpad-brightness-down
# 
# event=video/brightnessdown BRTDN 00000087 00000000
# action=/etc/acpi/thinkpadbrightness.sh down
#
# put this to /etc/acpi/events/thinkpad-brightness-up
# 
# event=video/brightnessup BRTUP 00000086 00000000
# action=/etc/acpi/thinkpadbrightness.sh up

MIN_BRIGHTNESS=100
CHANGES=20

MAX_BRIGHTNESS=$(cat /sys/class/backlight/intel_backlight/max_brightness)
BRIGHTNESS=$(cat /sys/class/backlight/intel_backlight/brightness)

BRIGHTNESS_CHANGE=$(( $MAX_BRIGHTNESS / $CHANGES ))

DOWN_BRIGHTNESS=$(( $BRIGHTNESS - $BRIGHTNESS_CHANGE ))
UP_BRIGHTNESS=$(( $BRIGHTNESS + $BRIGHTNESS_CHANGE ))


if [ "x$1" = "xdown" ]; then
	if [ "$DOWN_BRIGHTNESS" -lt "$MIN_BRIGHTNESS" ]; then
		DOWN_BRIGHTNESS=$MIN_BRIGHTNESS
	fi

	echo $DOWN_BRIGHTNESS > /sys/class/backlight/intel_backlight/brightness
elif [ "x$1" = "xup" ]; then
	if [ "$UP_BRIGHTNESS" -gt "$MAX_BRIGHTNESS" ]; then
		UP_BRIGHTNESS=$MAX_BRIGHTNESS
	fi
	echo $UP_BRIGHTNESS > /sys/class/backlight/intel_backlight/brightness
else
   echo >&2 Unknown argument $1
fi