Backlight control helper for laptops running intel and NVIDIA cards.

brightnessctl.sh

#!/bin/bash

PRIME_MODE=`prime-select query`
IS_NVIDIA=false

if [ "$PRIME_MODE" == "nvidia" ]; then
  IS_NVIDIA=true

fi

NVIDIA_BACKLIGHT=/sys/class/backlight/intel_backlight/brightness

BRIGHTNESS=100
MAX_BRIGHTNESS=100
SINGLE_STEP=1
STEP=$(echo "$SINGLE_STEP * 5" | bc)

check_nvidia() {
  if [[ $IS_NVIDIA -ne false ]]; then
    echo "NVIDIA GPU enabled, can't proceed!"
    exit 1
  fi
}

get_brightness() {
  if [[ $IS_NVIDIA ]]; then
    REAL_BRIGHTNESS=$(cat /sys/class/backlight/intel_backlight/brightness)
    MAX_BRIGHTNESS=$(cat /sys/class/backlight/intel_backlight/max_brightness)
    SINGLE_STEP=$(echo "$MAX_BRIGHTNESS/100" | bc | cut -f1 -d ".")
    BRIGHTNESS=$(echo "$REAL_BRIGHTNESS/$SINGLE_STEP" | bc) 
  else
    REAL_BRIGHTNESS=$(xbacklight | awk '{print int($1+0.5)}')
    BRIGHTNESS=$REAL_BRIGHTNESS
  fi
}

get_brightness

if [ $BRIGHTNESS -lt 50 ]; then
  STEP=3
fi

if [ $BRIGHTNESS -lt 5 ]; then
  STEP=1
fi

case "$1" in
  get)
    echo $BRIGHTNESS
    ;;

  set)
    if [[ $IS_NVIDIA ]]; then
      echo $(echo $SINGLE_STEP * $2 | bc) | sudo tee $NVIDIA_BACKLIGHT
    else 
      xbacklight -set $2
    fi
    get_brightness
    echo $BRIGHTNESS
    ;;

  real)
    echo $REAL_BRIGHTNESS
    ;;

  up)
    if [[ $IS_NVIDIA ]]; then
      NEW_VALUE=$(echo "$REAL_BRIGHTNESS + ($SINGLE_STEP * $STEP)" | bc)
      echo $NEW_VALUE | sudo tee $NVIDIA_BACKLIGHT
    else 
      xbacklight -inc $STEP
    fi
    get_brightness
    echo $BRIGHTNESS
    ;;
  down)
    if [[ $IS_NVIDIA ]]; then
      NEW_VALUE=$(echo "$REAL_BRIGHTNESS - ($SINGLE_STEP * $STEP)" | bc)
      if [[ "$NEW_VALUE" -lt 1 ]]; then
        echo 1 | sudo tee $NVIDIA_BACKLIGHT
      else 
        echo $NEW_VALUE | sudo tee $NVIDIA_BACKLIGHT
      fi
    else 
      xbacklight -dec $STEP
    fi
    get_brightness
    echo $BRIGHTNESS
    ;;
  reset)
    if [[ $IS_NVIDIA ]]; then
      echo $(echo "$SINGLE_STEP * 20" | bc) | sudo tee $NVIDIA_BACKLIGHT
    else
      xbacklight -set 20
    fi
    get_brightness
    echo $BRIGHTNESS
    ;;
  *)
    echo "./brightnessctl.sh <get|up|down>"
    exit 1
    ;;
esac

On my Dell XPS 15, running ubuntu Ubuntu 16.04, xbacklight doesn't do the right thing when nvidia card is selected. Then again, when running on intel, xbacklight works, but /sys/class/backlight/intel_backlight/brightness doesn't. So I wrote this helper that I use this with i3wm, commands up / down mapped to hardware brightness control keys, and i3 toolbar is reading outputs of get -command.

Works at least on 4.4.0-43-generic kernel.