#!/bin/sh

# default
step=+5

video_card=$(ls -1 /sys/class/backlight/)
cur_brightness=$(cat /sys/class/backlight/"$video_card"/brightness)
max_brightness=$(cat /sys/class/backlight/"$video_card"/max_brightness)

while getopts s: flag
do
    case "${flag}" in
        s) step=${OPTARG};;
        *) echo "Usage: -s <-value/+value>";;
    esac

done

step=$(echo "$step" | sed 's/+//g')
step_c=$(( (step*max_brightness)/100 ))
# step_c=$(echo "scale=2; $step*($max_brightness/100)" | bc -l | sed 's/\..*$//')
new_brightness=$((cur_brightness + step_c))

if [ "$new_brightness" -le "0" ]; then
    echo "0" > /sys/class/backlight/"$video_card"/brightness
elif [ "$new_brightness" -ge "$max_brightness" ] ; then
    echo "$max_brightness" > /sys/class/backlight/"$video_card"/brightness
else
    echo "$new_brightness" > /sys/class/backlight/"$video_card"/brightness
fi