backlight control

blctl.sh

#!/bin/bash -e

path=/sys/class/backlight/intel_backlight
factor=10

usage() {
	echo "usage: ${0##*/} [-l label] [-f path] {up|down|raise|lower} [n]" >&2
	echo "       ${0##*/} [-l label] [-f path] set <n>" >&2
	echo "       ${0##*/} [-l label] [-f path] get" >&2
	exit 1
}

percent() {
	echo $(( 100 * $1 / $max ))
}

absolute() {
	echo $(( $1 * $max / 100 ))
}

while getopts l: c; do
	case $c in
	f)
		path="$OPTARG"
		;;

	?)
		usage
		;;
	esac
done
shift $(($OPTIND - 1))

if [ ! -d "$path" ]; then
	echo "could not stat $path" >&2
	exit 1
fi

max="$(< ${path}/max_brightness)"
cur="$(< ${path}/actual_brightness)"

setbl() {
	new=$1

	if [ $new -gt $max ]; then
		new=$max
	elif [ $new -le 0 ]; then
		new=1
	fi

	echo $new > $path/brightness
}

case "$1" in
up|down|raise|lower)
	if [ $# -gt 2 ]; then
		usage
		exit
	elif [ $# -eq 2 ]; then
		factor="$2"
	fi

	if [ ! \( "$factor" -ge 0 -a "$factor" -le 100 \) ]; then
		echo "out of range" >&2
		exit 1
	fi

	new=`absolute $factor`

	case "$1" in
	up)    setbl $(( $cur + $new    )) ;;
	down)  setbl $(( $cur - $new    )) ;;
	raise) setbl $(( $cur * $factor )) ;;
	lower) setbl $(( $cur / $factor )) ;;
	esac
	;;

set)
	if [ $# -ne 2 ]; then
		usage
		exit
	fi

	newp="$2"

	if [ ! \( "$newp" -ge 0 -a "$newp" -le 100 \) ]; then
		echo "out of range" >&2
		exit 1
	fi

	setbl $(( $max * $newp / 100 ))
	;;

get)
	percent $cur
	;;

*)
	usage
	exit 1
	;;
esac