#!/bin/bash

operation="${1}"
brightness="$(cat /sys/class/leds/lcd-backlight/brightness)"

case "$operation" in
  up)
    echo "$(( ${brightness} + 15 ))" > /sys/class/leds/lcd-backlight/brightness
    ;;
  down)
    echo "$(( ${brightness} - 15 ))" > /sys/class/leds/lcd-backlight/brightness
    ;;
esac