#!/bin/bash
#
# t440p brightness control
# /etc/acpi/brightness

bl_dev=/sys/class/backlight/intel_backlight
bl=${bl_dev}/brightness

step=200
curval=`cat $bl`
maxval=`cat /sys/class/backlight/intel_backlight/max_brightness`

case "$1" in
  -) let "step=step*-1";;
  +) ;;
  *) exit 1;;
esac

let "newval=curval+step"

if [ $newval -gt $maxval ]; then
  newval=$maxval
elif [ $newval -lt 0 ]; then
  newval=0
fi

echo $newval > $bl

# $ cat /sys/class/backlight/intel_backlight/brightness
# 1440
# $ cat /sys/class/backlight/intel_backlight/max_brightness
# 4794
# $ cat /sys/class/backlight/intel_backlight/actual_brightness
# 1440