#!/bin/bash
set -x

if xbacklight -get; then
  if [[ "$1" == "up" ]]; then 
    xbacklight -inc 20
  else
    xbacklight -dec 20
  fi
else
  val=$(cat /sys/class/backlight/*/brightness | head -1)
  if [[ "$1" == "up" ]]; then
    val=$((val+20))
  else
    val=$((val-20))
  fi
  for bk in /sys/class/backlight/*; do
    echo $val > $bk/brightness
  done
fi