battery_monitor

#!/bin/bash

get_battery_level() {
  # Initialize variables
  total_battery_level=0

  # If any batteries exist, enter loop
  if compgen -G "/sys/class/power_supply/BAT*" > /dev/null; then
    # Iterate over all of the batteries
    for battery_path in "/sys/class/power_supply/BAT"*; do
      # Get battery information
      battery_level=$(cat "${battery_path}/capacity")
      total_battery_level=$(( battery_level + total_battery_level ))

      # Return the battery level
      echo "${total_battery_level}"
    done
  fi
}

get_ac_status(){
    if ! [[ $(cat "/sys/class/power_supply/A"[CD]*"/online") -ge '1' ]]; then
      echo 'Discharging'
    else
      echo 'Charging'
    fi
}

battery_level="$(get_battery_level)"
ac_status="$(get_ac_status)"
export DBUS_SESSION_BUS_ADDRESS="unix:path=/run/user/${UID}/bus"
export DISPLAY=':0'
display_ids=()

for display_proc in $(for proc_file in /proc/[0-9]*; do
                      grep -ao 'DISPLAY=[^[:cntrl:]]*' "${proc_file}/environ" 2>/dev/null
                    done|sort|uniq|awk -F'=' '{print $2}'); do
  display_ids+=("${display_proc}")
done

for display_id in "${display_ids[@]}"; do
  export DISPLAY="${display_id}"
  if [[ "${ac_status}" == 'Discharging' && "${battery_level}" -lt 30 ]]; then
    notify-send -t 59000 -u critical \
      -a "battery_monitor" \
      "Battery is Low." \
      "Level: $battery_level %"
  fi
done