bat-status-changed.sh

#!/usr/bin/env bash

# this script is run whenever the status of the AC adapter changes

# user who is expected to be running the x server (i.e. has Xauthority)
XUSER="cmyers"

# how long a delay between plugging in power and battery status no longer shows discharging
SLEEP_DELAY="0.5s"

# how dim should it be on battery?
BAT_BRIGHTNESS="70%"

# if we run the script directly, display will already be right, but when udev runs it we need to fill this in
export DISPLAY="${DISPLAY:-:0.0}"

# I've seen the following possible values: Unknown, Discharging, Charging, Full.
# you may have to customize this value for your laptop
# You can probably discover the value with: find /sys/devices/ -type d -name 'BAT0'
BAT_FILE="/sys/devices/LNXSYSTM:00/LNXSYBUS:00/PNP0A08:00/device:1b/PNP0C09:00/PNP0C0A:00/power_supply/BAT0/status"

# Implementation Notes:
# When the AC adaptor is unplugged, the status is updated almost immediately
# However, when the AC adaptor is plugged in, it sometimes takes a second or
# two for it to update.  For this reason, instead of having a udev rule for
# plug in and a udev rule for unplug, we instead have a rule that triggers on
# any change and runs this script which will then sleep for a second, then do
# the needful.

# To install the udev rule, as root:
# echo 'KERNEL=="BAT0", RUN+="/bin/bash /home/cmyers/bin/bat-status-changed.sh"' > /etc/udev/rules.d/49-powersave.rules
#
# If your battery has a different name or is weird or whatever, you can replace KERNEL=="BAT0" with SUBSYSTEM="power_supply".

function switch_to_battery {
    # Put anything you want to happen when on battery power here

    # set screensaver to blank only
    sed -i 's/^mode:.*/mode: blank/' /home/cmyers/.xscreensaver;

    # dim LCD
    sudo -u "$XUSER" /usr/bin/xbacklight -set "$BAT_BRIGHTNESS";
}

function switch_to_ac {
    # Put anything you want to happen when on AC power here

    # set screensaver to back to the one true screensaver (xmatrix)
    sed -i 's/^mode:.*/mode: one/' /home/cmyers/.xscreensaver;

    # restore LCD to 100%
    sudo -u "$XUSER" /usr/bin/xbacklight -set "100%";
}

sleep "$SLEEP_DELAY"
BAT_STATUS="$(cat "$BAT_FILE")"

if [[ "$BAT_STATUS" == "Discharging" ]]; then
    # we are on battery
    switch_to_battery
    exit 0;
fi

# for all others, assume we are on AC (Charging, Full are almost always AC, Unknown is probably AC too)
switch_to_ac
exit 0;