GPIO

#!/bin/bash
 
# …
ports="/sys/class/gpio/gpio21/value /sys/class/gpio/gpio21/value"
 
# Schleife
while [ true ] ; do 
	for port in ${ports} ; do
		v=$(< ${port})
		#echo "Debug: ${port} = ${v}"
		if [ ${v} = 1 ]; then 
			echo "Pin an"
		else
			echo "Pin aus"
		fi
	done
	sleep 1s
done