#!/bin/bash

trap "echo \"4\" >/sys/class/gpio/unexport" EXIT

echo "4" >/sys/class/gpio/export
echo "out" >/sys/class/gpio/gpio4/direction

while true
do
    echo "1" >/sys/class/gpio/gpio4/value
    sleep 1
    echo "0" >/sys/class/gpio/gpio4/value
    sleep 1
done