An xbacklight (semi)-compatible alternative for unsupported systems (specifically my System76 machine)

xbacklight.sh

#!/bin/bash

function usage {
	echo "usage: $0 [options]"
	echo "  where options are:"
	echo "  -help"
	echo "  -set <percentage> or = <percentage>"
	echo "  -inc <percentage> or + <percentage>"
	echo "  -dec <percentage> or - <percentage>"
	echo "  -get"
}


if [ $# -gt 0 ]; then
	CURRENT="$(cat /sys/class/backlight/intel_backlight/brightness)"
	MAX="$(cat /sys/class/backlight/intel_backlight/max_brightness)"
	if [ "$1" == "-get" ]; then
		PERCENT="$(( MAX / CURRENT ))"
		PERCENT="$(( 100 / PERCENT ))"
		echo "$PERCENT%"
	elif [ "$1" == "-set" ] || [ "$1" == "=" ]; then
		if [ $# -gt 1 ]; then
			if [ "$2" -eq "$2" ]; then #Bash hack to see if it's a number
				if [ "$2" -lt 101 ] && [ "$2" -gt -1 ]; then
					VALUE="$(( MAX*$2/100 ))"
					echo $VALUE > /sys/class/backlight/intel_backlight/brightness
				else
					echo "Error: <percentage> argument must be between 0 and 100"
					usage
				fi
			else
				echo "Error: <percentage> argument must be an integer"
				usage
			fi
		else
			echo "Error: Missing <percentage> arguement"
			usage
		fi
	elif [ "$1" == "-inc" ] || [ "$1" == "+" ]; then
		if [ $# -gt 1 ]; then
			if [ "$2" -eq "$2" ]; then #Bash hack to see if it's a number
				if [ "$2" -lt 101 ] && [ "$2" -gt -1 ]; then
					VALUE="$(( ( MAX*$2/100 ) + CURRENT ))"
					echo $VALUE > /sys/class/backlight/intel_backlight/brightness
				else
					echo "Error: <percentage> argument must be between 0 and 100"
					usage
				fi
			else
				echo "Error: <percentage> argument must be an integer"
				usage
			fi
		else
			echo "Error: Missing <percentage> arguement"
			usage
		fi
	elif [ "$1" == "-dec" ] || [ "$1" == "-" ]; then
		if [ $# -gt 1 ]; then
			if [ "$2" -eq "$2" ]; then #Bash hack to see if it's a number
				if [ "$2" -lt 101 ] && [ "$2" -gt -1 ]; then
					VALUE="$(( CURRENT - (MAX*$2/100) ))"
					echo $VALUE > /sys/class/backlight/intel_backlight/brightness
				else
					echo "Error: <percentage> argument must be between 0 and 100"
					usage
				fi
			else
				echo "Error: <percentage> argument must be an integer"
				usage
			fi
		else
			echo "Error: Missing <percentage> arguement"
			usage
		fi
	fi
else
	usage
fi