#!/bin/bash

# base dir for backlight class
basedir="/sys/class/backlight/"

# get the backlight handler
handler=$basedir$(ls $basedir)"/"

# get current brightness
old_brightness=$(cat $handler"brightness")

# get max brightness
max_brightness=$(cat $handler"max_brightness")

# calculate new brightness % 
new_brightness=$(($old_brightness $1))

if [ new_brightness -lt 0 ]; then
	new_brightness = 0
elif [ new_brightness -gt $max_brightness ]; then
	new_brightness = $max_brightness
fi

# set the new brightness value
#sudo chmod 666 $handler"brightness"
echo $new_brightness > $handler"brightness"