Battery Alert to NTFY using Bash
Recently I’ve started an experiment to use an old laptop as an Ubuntu server. The reason is twofold, to see how it handles different types of loads and to have a built-in battery to keep certain services up. I’ll write up on how I set that up in the future, once it’s had some time to generate data. Aside from powertop to tune the power consumption I wanted to be alerted when the charge state changes or it goes above or below certain thresholds. Starting with NTFY and the post on Network Chuck’s site as a start, it needed a few tweaks to get working for me, it was time to open a shell and nano and get to work. Also, side note some of the tweaking was done with the help of Google Bard and various Stackoverflow posts.
Outlining the Script
Here is the basic script loop a few precursors, for error handling and a global variable to handle state change tracking in the loop, more on that later. Here’s the basic loop.
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#!/bin/bash
trap 'echo "Error executing the curl command: $?"'
PREVIOUS_STATUS=""
while true; do
sleep 300 # Adjust polling time here in seconds
done
Checking Batter Charge Percentage and State
The reason for this feature is to know when the laptop is either unplugged or the power is out.
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# Get the current battery level
BATTERY_LEVEL=$(cat /sys/class/power_supply/BAT0/capacity) # Charge Percentage
BATTERY_STATUS=$(cat /sys/class/power_supply/BAT0/status) # Charging Status
Triggering Alert on Status Change
For my situation I need to to pull the status(and charge percentage) from /sys/class/power_supply/BAT0, ymmv. Here’s the logic that takes care of that, this goes inside the while loop.
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if [[ "$BATTERY_STATUS" != "$PREVIOUS_STATUS" ]]; then
curl -s -o /dev/null --max-time 10 -d "Battery charging status has changed to $BATTERY_STATUS." https://ntfy.saltyoldgeek.com/asus1
fi
Trigger on upper and lower thresholds
This one is pretty straightforward, we are comparing both the charge state and battery percentage, no need to keep reporting a low battery if it’s charging.
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if [[ "$BATTERY_LEVEL" -ge 80 ]] && [[ "$BATTERY_STATUS" == "Charging" ]]; then
curl -s -o /dev/null --max-time 10 -d "Asus 1 battery at or above 80%!!" https://ntfy.saltyoldgeek.com/asus1
elif [[ "$BATTERY_LEVEL" -le 50 ]] && [[ "$BATTERY_STATUS" == "Discharging" ]]; then
curl -s -o /dev/null --max-time 10 -d "Asus 1 battery low" https://ntfy.saltyoldgeek.com/asus1
fi # Wait for 5 minutes (300 seconds) before checking again
Setting Status check variable and sleep
This last one is setting up the previous status to compare with the next pull at the top of the loop, we need this set here in order to have a status compare up top, this is also why the variable PREVIOUS_STATUS is set to an empty string before the loop to keep it from erroring out on the first pass.
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PREVIOUS_STATUS="$BATTERY_STATUS"
sleep 300
TLDR: Here’s the scripts in it’s entirety
Here’s the whole script, If you find this helpful let me know on my socials, or better yet, send support me over at Ko-fi. Till the next one, fair winds and following seas.
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#!/bin/bash
trap 'echo "Error executing the curl command: $?"' ERR
PREVIOUS_STATUS=""
while true; do
# Get the current battery level
BATTERY_LEVEL=$(cat /sys/class/power_supply/BAT0/capacity) # Check if the battery level is below 20%
BATTERY_STATUS=$(cat /sys/class/power_supply/BAT0/status)
if [[ "$BATTERY_STATUS" != "$PREVIOUS_STATUS" ]]; then
curl -s -o /dev/null --max-time 10 -d "Battery charging status has changed to $BATTERY_STATUS." https://ntfy.saltyoldgeek.com/asus1
fi
if [[ "$BATTERY_LEVEL" -ge 80 ]] && [[ "$BATTERY_STATUS" == "Charging" ]]; then
curl -s -o /dev/null --max-time 10 -d "Asus 1 battery at or above 80%!!" https://ntfy.saltyoldgeek.com/asus1
elif [[ "$BATTERY_LEVEL" -le 50 ]] && [[ "$BATTERY_STATUS" == "Discharging" ]]; then
curl -s -o /dev/null --max-time 10 -d "Asus 1 battery low" https://ntfy.saltyoldgeek.com/asus1
fi # Wait for 5 minutes (300 seconds) before checking again
PREVIOUS_STATUS="$BATTERY_STATUS"
sleep 300
done