Click counter when link is clicked PHP/JS

I have a little script here that counts clicks when link is clicked and stores it in .txt file, but it works fine when I have only "click=yes" under href. But I can't make it to track clicks when I have link to external site.

Here is my code:

<?php
if(!file_exists('counter.txt')){
file_put_contents('counter.txt', '0');
}
if($_GET['click'] == 'yes'){
file_put_contents('counter.txt', ((int) file_get_contents('counter.txt')) + 1);
header('Location: ' . $_SERVER['SCRIPT_NAME']);
die;
}
?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>counter example</title>
</head>
<body>
<h1><?php echo file_get_contents('counter.txt'); ?></h1>
<a href="http://www.google.com?click=yes" target="new">clickMe</a>
</body>
</html>

My guess is it has to do something with header('Location: ' . $_SERVER['SCRIPT_NAME']); but I can't figure it out so I could really use some help.

And is it somehow possible to have multiple links save to the same file, and when I show it on website it's sorted from largest number to smallest? I have an idea how to do it with MySQL database but I can't use it at place where this will be implemented.

Thanks in advance! Cheers!

Solution

Your server never sees the URI being accessed as the client leaves your page. To do something like this, it may be best to set up a redirect which works like this

<a href="/goto.php?href=http://www.google.com" target="_blank">click me</a>

(Make sure the external site's URL is URL encoded as you're passing it as a GET component of a URL to your own page)

Then in goto.php you store your click and send a redirect header

if(!file_exists('counter.txt')){
    file_put_contents('counter.txt', '0');
}
file_put_contents('counter.txt', ((int) file_get_contents('counter.txt')) + 1);
header('Location: ' . $_GET['href']);

Now you can track these clicks, you can add your domain-specific counters in goto.php instead of your text file