#!/bin/bash

[[ -n "$BACKLIGHT" ]] || BACKLIGHT=intel_backlight
fmax=/sys/class/backlight/$BACKLIGHT/max_brightness
fcur=/sys/class/backlight/$BACKLIGHT/brightness
read max < $fmax || exit $?
case $# in
	0)
		read cur < $fcur
		bc <<<"100*$cur/$max" | cut -d. -f1
		;;
	1)
		declare -i pct="$1"
		bc <<<"$max*$pct/100" | cut -d. -f1 > $fcur
		;;
	*)
		echo "Usage: [BACKLIGHT=<device_id>] backlight [<percent>]" >&2
		exit 1
		;;
esac