Shell file to notify when your laptop battery life is less than 20% or more than 90% as is charging

battery-notifier.sh

 #!/bin/bash

while true
do
    export DISPLAY=:0.0
    battery_level=`acpi -b | grep -P -o '[0-9]+(?=%)'`
    if on_ac_power; then
        if [ $battery_level -ge 90 ]; then
            notify-send "Battery charging above 90%. Please unplug your AC adapter!" "Charging: ${battery_level}% "
            spd-say "charge full, fulll, full"
            sleep 20
            if on_ac_power; then
                gnome-screensaver-command -l   ## lock the screen if you don't unplug AC adapter after 20 seconds
            fi
         fi
    else
         if [ $battery_level -le 20 ]; then
            notify-send "Battery is lower than 20%. Need to charg! Please plug your AC adapter." "Charging: ${battery_level}%"
            spd-say "battery low, low, low"
            sleep 20
            if ! on_ac_power; then
                gnome-screensaver-command -l   ## lock the screen if you don't plug AC adapter after 20 seconds
            fi
         fi
    fi

    sleep 120 # 120 seconds or 2 minutes
done