Set brightness via radeon_bl0 when redshift status changes

gistfile1.txt

#!/bin/bash

# Set brightness via radeon_bl0 when redshift status changes (amdgpu,radeon)
### Set brihtness via xbrightness when redshift status changes


# Set brightness values for each status.
# Range from 1 to 255 is valid
brightness_day="255"
brightness_transition="120"
brightness_night="30"
# Set fade time for changes to one minute
fadetime=60

old_brightness_v=\$brightness_${2}
new_brightness_v=\$brightness_${3}
old_brightness=`eval echo $old_brightness_v`
new_brightness=`eval echo $new_brightness_v`

case $1 in
	period-changed)
		if [[ $old_brightness -gt $new_brightness ]]; then
		  while [[ $old_brightness -gt $new_brightness ]]; do
		    echo $old_brightness > /sys/class/backlight/radeon_bl0/brightness
		    sleep $fadetime
                    ((old_brightness -= 1))
		  done & 
		fi
                if [[ $old_brightness -lt $new_brightness ]]; then
                  while [[ $old_brightness -lt $new_brightness ]]; do
                    echo $old_brightness > /sys/class/backlight/radeon_bl0/brightness
                    sleep $fadetime
                    ((old_brightness += 1))
                  done &
                fi
	;;
esac

You can use [ ... ] instead of [[ ... ]], or test ... as I would prefer. If you then use expr instead of (( )), the script should run nicely in POSIX sh on any system. To improve performance (assuming using sh instead of bash) but lose portability, you can use for and seq instead of the counter.

You may also want to look at the file max_brightness instead of assuming that the maximum value is 255, it seldom is. Some user's may want to test setting the brightness to their value on brightness_night and then reset the brightness, before putting this in production; some drives will get locked until reboot when the brightness is too low.