checkbacklight

#!/bin/bash
#	checkbacklight - script to hook udev and set min/max backlight

# Set paths for the udev rule and settings file
rule="/etc/udev/rules.d/99-checkbacklight.rules"
settings="/etc/default/backlight"

# Check for root permissions
if [ "$(id -u)" == 0 ]; then

	if [ ! $(which checkbacklight) ]; then

		echo "script isn't executable in root's PATH."

		exit 1

	fi

else

	echo "You must be root to use this script."

	exit 1

fi

# Check for backlightctl
if [ ! $(which brightnessctl) ]; then

	echo "brightnessctl not found, please install."

	exit 1

fi

# Check for settings file, create if doesn't exist
if [ ! -f "$settings" ]; then

	echo "# Default settings for backlight" > "$settings"
	echo "#  WARNING: there is no stupid-user protection here," >> "$settings"
	echo "#   DO NOT set max_brightness to 0 or something." >> "$settings"
	echo "max_brightness=$(brightnessctl m)" >> "$settings"
	echo "min_brightness=0" >> "$settings"

fi

# Check for udev rule, create if doesn't exist
if [ ! -f "$rule" ]; then

	echo "ACTION=='change', SUBSYSTEM=='backlight', RUN+='$(which checkbacklight)'" > "$rule"

	udevadm control --reload-rules

	echo "udev rule created."

	exit 0

fi

# Read settings file
source "$settings"

# Check the current brightness level
current_brightness=$(brightnessctl g)

# Adjust brightness if too high/low based on settings file
if [ $(("$current_brightness")) -gt $(("$max_brightness")) ]; then

        brightnessctl s "$max_brightness"

elif [ $(("$current_brightness")) -lt $(("$min_brightness")) ]; then

	brightnessctl s "$min_brightness"

fi