note to self: in /usr/local/bin

brightness.sh

#!/bin/bash
curr_brightness=$(cat /sys/class/backlight/intel_backlight/brightness)
curr_brightness=$(($curr_brightness))
max_brightness="$(cat /sys/class/backlight/intel_backlight/max_brightness)"
max_brightness=$(($max_brightness))
brightness=0
# -10%: decrease by a percentage, not going below 0
# +10%: increase by a percentage, not going above $max_brightness
# 10%: set to an absolute percentage between 0 and $max_brightness
# 10: set to an absoulte brightness not exceeding #max_brightness
case $1 in
    incp)
        brightness=$(($curr_brightness + $max_brightness * $2 / 100))
        ;;
    inc)
        brightness=$(($curr_brightness + $2))
        ;;
    setp)
        brightness=$(($max_brightness * $2 / 100))
        ;;
    "set")
        brightness=$(($2))
        ;;
esac

((brightness = $brightness > $max_brightness ? $max_brightness : $brightness))
((brightness = $brightness < 1 ? 1 : $brightness))
echo "$curr_brightness -> $brightness"
echo $brightness > /sys/class/backlight/intel_backlight/brightness