xbacklight script for Lenovo Y500

#!/bin/bash

# Script for setting the correct brightness for the backlight.
# Depends on: xbacklight and inotify-tools,
# Which can be installed by running:
#       `sudo apt-get install xbacklight inotify-tools`
#
# Author: Esteban Serrano Roloff <e.serrano.r (at) me.com>
#
# Tested on a Sony VAIO VPCCW15FL
# running Ubuntu 12.04
# 2013-03-27 (YYYY-MM-DD)

# Setup the correct paths (look inside /sys/class/backlight/)
current_brightness_path="/sys/class/backlight/acpi_video0/brightness"
max_brightness_path="/sys/class/backlight/acpi_video0/max_brightness"
# To find the correct value for min_brightness, make the
# brightness meter go to its minimum (by repeatedly pressing
# the brightness down key), even if the actual brightness stays
# the same, and then run on a terminal:
#       `cat /sys/class/backlight/sony/brightness`
min_brightness=0


#### No editing needed beyond this line (I hope) ####
max_brightness=`cat $max_brightness_path`
range=${max_brightness-min_brightness}



# Set the correct brightness level on start up.
current_brightness=`cat $current_brightness_path`
let current_brightness_pctg=100*$current_brightness/$range
xbacklight =$current_brightness_pctg

# Listen for brightness changes, forever.
while inotifywait -e close_write $current_brightness_path; do

    current_brightness=`cat $current_brightness_path`
    let current_brightness_pctg=100*$current_brightness/$range
    xbacklight =$current_brightness_pctg

done