how to track referrer at session start?

I'd like to do the following:
1. when a user enters the website, check their referrer
2. store it in a session variable
3. at any point when they convert in any way (contact form, eval form, etc), I store the referrer in a hidden field

Any ideas? I know how to do this in ASP, with the session_onstart sub, but how do I do it with PHP?

 

if($_SERVER['HTTP_REFERER']){
$_SESSION['referer'] = $_SERVER['HTTP_REFERER'];
}

 

will this count only URLs from external domains as referrers?

 

You could do something like:

if ( ! isset( $_SESSION[ 'referer' ] ) ) {
    if ( $_SERVER[ 'HTTP_REFERER' ] ) {
        $_SESSION[ 'referer' ] = $_SERVER[ 'HTTP_REFERER' ];
    }
}

Code (markup):

and that will set it only if it hasn't already been set for this session.

 

thank you. But will this track referrals from external domains only?

 

it will refer internal links.

my guess is that you should add a preg_match statement
to weed out your domain name.

 

am I wrong in assuming that it would only do this if someone came to the site directly, then clicked? In which case, could I not on first check just set the session variable to 'direct' if there is no http referrer?

 

$host = parse_url(str_replace('www.', null, $_SERVER['HTTP_HOST']));
$referer = parse_url(str_replace('www.', null, $_SERVER['HTTP_REFERER']));

if (isset($referer['host']) AND $referer['host'] != $host['host'])
{
	$_SESSION['referer'] = $_SERVER['HTTP_REFERER'];
}

PHP:

Untested.

 

awesome, thanks everyone!