#!/bin/bash
hostname=`hostname`
max_brightness=`cat /sys/class/backlight/intel_backlight/max_brightness`
brightness=`cat /sys/class/backlight/intel_backlight/brightness`
step=$(( max_brightness / 6 ))
inc=2
low_delta=$(( brightness - step ))
high_delta=$(( brightness + step ))

if ( [ $1 = 'down' ] && [ $low_delta -gt 0 ] )  ||  ( [ $1 = 'up' ] && [ $high_delta -lt $max_brightness ] )
then
    for i in $(seq $step); do
        case $1 in
        'up')
            brightnessctl s +$inc 1> /dev/null
        ;;
        'down')
            brightnessctl s $inc- 1> /dev/null
        ;;
        esac
    done
else
    echo 'Brightness too high. Use `off` parameter to turn backlight off'
fi