The script is also a wrapper wether you have (xorg-)xbacklight installed or not, but if not, it requires sudo to be passwordless for the user (if called by a WM/without using terminal).
#!/usr/bin/env bash
# Description: Change brightness of laptop lcd
# This script is part of my AwesomeWM configuration (https://github.com/sri-arjuna/awesome)
# The most recent version should be available on: https://raw.githubusercontent.com/sri-arjuna/awesome/master/scripts/brightness.sh
# Disclaimer: This code comes without any warrenty of any kind, use at your own risk!
# GNU General Public License (GPL) 2016 by Simon Arjuna Erat (sea) (erat.simon æ gmail,com)
#
#
# Variables
#
BASE=/sys/class/backlight
ITEM=$(cd $BASE;ls)
DIR=$BASE/$ITEM
FILE=$DIR/backlight
MAX=$(<$DIR/max_backlight)
STEP_COUNT=20
STEP_VALUE=$(( $MAX / $STEP_COUNT ))
CUR=$(<$FILE)
#
# Action
#
if which xbacklight 2>/dev/null >&2
then # xbacklight is installed
#cur=$(xbacklight)
#cur=${cur/\.*}
case "${1,,}" in
"") echo "Usage: brightness.sh up|down"
exit 1
;;
up) xbacklight -inc 20
;;
down) xbacklight -dec 20
;;
esac
else # Fallback, dont like the use of sudo in a background script
# Required/recomend passwordless sudo, but is a security risk!
case "${1,,}" in
"") echo "Usage: brightness.sh up|down"
exit 1
;;
up) num=$(( $CUR + $STEP_VALUE ))
[ $num -ge $MAX ] && num=$MAX
[ $num -le 0 ] && num=0
sudo tee $FILE <<< $num
;;
down)
num=$(( $CUR - $STEP_VALUE ))
[ $num -ge $MAX ] && num=$MAX
[ $num -le 0 ] && num=0
sudo tee $FILE <<< $num
;;
esac
fi
