#!/bin/bash

# Allows you to adjust display backlight from the command line.
# USAGE: backlight <brightness change>
# The brightness change can be positive (for brighter) or negative (for darker).
# NOTE: requires root privileges.

brightness=`cat /sys/class/backlight/intel_backlight/brightness`
delta="$1"

if [[ ! $delta =~ ^-?[0-9]+$ ]]; then
    echo "Not a number!"
    exit 1
fi

new_brightness=$((brightness + delta))


if [[ new_brightness -gt 7500 ]]; then
    new_brightness=7500
elif [[ new_brightness -lt 0 ]]; then
    new_brightness=0
fi

# echo $new_brightness
tee /sys/class/backlight/intel_backlight/brightness <<< "$new_brightness"