Simple caching with PHP

cache.php

<?php  
// define the path and name of cached file, 
$cachefile = 'cache/'.urlencode($_SERVER['REQUEST_URI']).'.txt';
       
// define how long we want to keep the file in seconds.
//$cachetime = 60*60*24;
$cachetime = 4;        
       
// Check if the cached file is still fresh. If it is, serve it up and exit.
if (file_exists($cachefile) && time() - $cachetime < filemtime($cachefile)) {
    echo "<h1>from cache</h1>";            
    include($cachefile);                   
    exit;     
}      
       
// if there is either no file OR the file to too old, render the page and capture the HTML.                                       
ob_start();
       
       
// Put all contents here.
echo "page contents at ".time();
       
       
// We're done! Save the cached content to a file
file_put_contents($cachefile, ob_get_contents()) or exit("Error! Check if cachefile is writable");
ob_end_flush();
?>