在X秒内刷新PHP变量[重复]

This question already has an answer here:

<?php 
  $test = file_get_contents("test.txt");
?>

<html>
   <body>
    <?php echo $test; ?>
  </body>
</html>

This is my code.

How can I refresh $test in 5 seconds?

</div>

Use ajax & setinterval

setInterval(function(){
 $('body').load('test.txt');
}, 5000);