To monitor the on/off status of a power supply using a GPIO input on a Raspberry Pi using shell commands, you can utilize the gpio command-line utility and some shell scripting. The gpio utility allows you to manipulate GPIO pins directly from the command line. Here's how you can do it:

Before you can use GPIO pins from the command line, you need to make sure they are enabled. You can do this by running:

sudo raspi-config

Then, navigate to "Interfacing Options" and enable the "GPIO" interface.

You can use the gpio command to read the status of a GPIO pin. For example, if you want to monitor GPIO17:

gpio read 17

This command will return 0 if the pin is LOW (off) and 1 if the pin is HIGH (on).

You can create a shell script to continuously monitor the GPIO pin's status and display it in the terminal. Here's a simple example:

#!/bin/bash

# Set the GPIO pin number
GPIO_PIN=17

# Configure the GPIO pin as an input
gpio mode $GPIO_PIN in

while true; do
    STATUS=$(gpio read $GPIO_PIN)
    
    if [ $STATUS -eq 1 ]; then
        echo "Power supply is ON"
    else
        echo "Power supply is OFF"
    fi
    
    sleep 5  # Adjust the sleep interval as needed
done

Save this script to a file (e.g., monitor_power_supply.sh) and make it executable:

The script will continuously check the status of the GPIO pin and print whether the power supply is ON or OFF. Remember to customize the GPIO_PIN variable with the actual GPIO pin number you are using, and adjust the sleep interval (sleep) to control how often the script checks the status.