backlight script for Lenovo ThinkPad P15s Gen 2i

backlight.sh

#!/bin/bash

# Example: increae brightness by 15%
# backlight.sh inc 15

CURRENT_BRIGHTNESS=$(cat /sys/class/backlight/intel_backlight/brightness)
MAX_BRIGHTNESS=$(cat /sys/class/backlight/intel_backlight/max_brightness)

ONE_PERCENT_FACTOR=$(( MAX_BRIGHTNESS / 100 ))

BRIGHTNESS_STEP=$2

case "$1" in
  -inc )
    NEW_BRIGHTNESS=$(( CURRENT_BRIGHTNESS + (BRIGHTNESS_STEP * ONE_PERCENT_FACTOR) ))
    ;;
  -dec )
    NEW_BRIGHTNESS=$(( CURRENT_BRIGHTNESS - (BRIGHTNESS_STEP * ONE_PERCENT_FACTOR) ))
    ;;
  *)
    echo $CURRENT_BRIGHTNESS ' / ' $MAX_BRIGHTNESS
    exit 0
    ;;
esac

NEW_BRIGHTNESS=$((NEW_BRIGHTNESS>MAX_BRIGHTNESS ? MAX_BRIGHTNESS : NEW_BRIGHTNESS))
NEW_BRIGHTNESS=$((NEW_BRIGHTNESS<0 ? 0 : NEW_BRIGHTNESS))

# need permissions to write:
# $ cat /etc/sudoers.d/intel_backlight
# ALL ALL = (ALL) NOPASSWD: /usr/bin/tee /sys/class/backlight/intel_backlight/brightness

echo $NEW_BRIGHTNESS | sudo tee /sys/class/backlight/intel_backlight/brightness