Remedy my laptop's the annoying behaviour of setting an arbitrary brightness upon wake from sleep.

brightness_restore.sh

#!/bin/sh

# Script to restore the last value for brightness upon ACPI wake.
#
# Hilariously, while you can write a new brightness to
#        /sys/class/backlight/intel_backlight/brightness, 
#
# to accurately determine the current brightness you must use
#        /sys/class/backlight/intel_backlight/actual_brightness, 

case $(cat /proc/acpi/button/lid/LID0/state | awk '{print $2}') in
    closed) cat /sys/class/backlight/intel_backlight/actual_brightness > /var/last_sleep_brightness ;;
    open) cat /var/last_sleep_brightness > /sys/class/backlight/intel_backlight/brightness && rm -f /var/last_sleep_brightness ;;
esac

gistfile1.sh

# /etc/acpi/events/brightness_restore

# For some reason my Acer Aspire TimelineX 1830T generates a battery event,
# with an identifiable code, when it wakes from sleep. I figured this out with
# acpi_listen. On sleep, it generates a button/lid event.

event=button/lid|battery BAT0 00000081
action=/etc/acpi/brightness_restore.sh