/main.php

## main.php
<?php
exec('bash ./script.sh > /dev/null &');
//or like exec('php ./run_backup.php > /dev/null &');

## script.sh
sleep 10
echo works > test.txt
	<?php
	exec('bash ./script.sh > /dev/null &');
	//or like exec('php ./run_backup.php > /dev/null &');