Script to set/increase/decrease brightness in Ubuntu 17.04

brightness.sh

#!/bin/bash

# Script to set/increase/decrease brightness in Ubuntu

MAX_BRIGHTNESS=$(cat /sys/class/backlight/intel_backlight/max_brightness);
BRIGHTNESS=$(cat /sys/class/backlight/intel_backlight/actual_brightness);
PCT=$(echo $BRIGHTNESS $MAX_BRIGHTNESS  | awk '{printf "%4.0f\n",($1/$2)*100}')

if [ "$(whoami)" != "root" ] ; then
        printf "Script must be run as root.\n" && exit;
fi

if [[ $1 == "-s" ]] || [[ $1 == "--set" ]]; then
        if [[ $1 -lt 0 ]] || [[ $1 -gt 100 ]]; then
                printf "Brightness must be between 0 and 100.\n" && exit;
        fi
        BRIGHTNESS=$(echo $2 $MAX_BRIGHTNESS  | awk '{printf "%4.0f\n",($1/100)*$2}')
elif [[ $1 == "-i" ]] || [[ $1 == "--inc" ]]; then
        BRIGHTNESS=$(echo $PCT $2 $MAX_BRIGHTNESS | \
                awk '{printf "%4.0f\n",(($1+$2)/100)*$3}')
elif [[ $1 == "-d" ]] || [[ $1 == "--dec" ]]; then
        BRIGHTNESS=$(echo $PCT $2 $MAX_BRIGHTNESS | \
                awk '{printf "%4.0f\n",(($1-$2)/100)*$3}')
else
        printf "Usage: brightness -s 50  # Set brightness at 50%%\n"
        printf "       brightness -i 10  # Increase brightness by 10%%\n"
        printf "       brightness -d 10  # Decrease brightness by 10%%\n"
fi

# Contstrain brightness to be in the range:
if [[ $BRIGHTNESS -gt $MAX_BRIGHTNESS ]]; then
        BRIGHTNESS=$MAX_BRIGHTNESS
elif [[ $BRIGHTNESS -lt 0 ]]; then
        BRIGHTNESS=0
fi

echo $BRIGHTNESS > /sys/class/backlight/intel_backlight/brightness