#!/bin/sh

BLDIR=`ls /sys/class/backlight/`

if [ "x$BLDIR" = "x" ]; then
    echo "No backlight device found."
    exit 0
fi

BLDIR="/sys/class/backlight/$BLDIR"

BR=`cat $BLDIR/brightness`
BR_MAX=`cat $BLDIR/max_brightness`

if [ $# -lt 1 ]; then
    echo "Usage: $0 0..$BR_MAX|+|-"
    exit 1
fi

D=$1

if [ $D = "+" ]; then
    BR=`expr $BR + 1`
    [ $BR -le $BR_MAX ] && echo $BR > $BLDIR/brightness
elif [ $D = "-" ]; then
    BR=`expr $BR - 1`
    [ $BR -ge 0 ] && echo $BR > $BLDIR/brightness
else
    expr $D + 0 >/dev/null 2>/dev/null || exit 1
    [ $D -ge 0 -a $D -le $BR_MAX ] && echo $D > $BLDIR/brightness
fi
