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Linux Server Hacks
By Rob Flickenger
January 2003
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HACK
#90
Simplistic Ad Referral Tracking
Create simple user tracking in print ads using the QUERY_STRING
Listing: referral-report.pl
[Discuss (1) | Link to this hack]

You're planning on advertising in a number of magazines, web sites, and newspapers, and you realize that you'd like to gauge how much traffic is coming in from each advertisement -- it'll help you better spend your money in the future. Unfortunately, you have no time to implement something complicated, so you're looking for a low-tech solution, as well as something that will make it easy to analyze the results.

Apache happily logs all environment variables passed to the pages it serves to the outside world. Thus, the hack is simple: pass an advertisement-based QUERY_STRING to the main page of your site. The QUERY_STRING will be ignored if you don't specifically act on it (with SSI, PHP, CGI, etc.), but Apache will still log the information to it's access_log.

For example, say you're advertising in the New York Times. Instead of saying "Come visit us at http://www.GatesMcFaddenCo.com," change the advertisement to specifically match the readership:

http://www.GatesMcFaddenCo.com/?nyt

In the above example, anytime someone types in that address, Apache will serve the main page normally but silently log that a QUERY_STRING of "nyt" has been passed. Using a log analyzer (like analog, or the simple one below), you can then find out how many people visited your site from seeing your ad in the New York Times.

Since you're using QUERY_STRINGs, you can also act upon them with Server Side Includes, PHP, or any other server-side language. For instance, the example HTML page below would show different greetings based on the web site address that the user typed in.

<html> 
<head> 
<title>Apache Hack #12396 - Simplistic Ad Referrel Tracker</title> 
</head> 
<body> 
<!--#if expr="\"$QUERY_STRING\" = \"nyt\"" --> 
<h1>Welcome New York Times Reader!</h1> 
<!--#elif expr="\"$QUERY_STRING\" = \"xml\"" --> 
<h1>Welcome XML.com Reader!</h1> 
<!--#else --> 
<h1>Welcome To Our Site!</h1> 
<!--#endif --> 
</body> 
</html>

The above will show special greetings if the user types in a QUERY_STRING that corresponds to advertisements at XML.com or at the New York Times. If the user didn't type in either, then a generic welcome is shown. Some sites have been known to change more than just the greeting, customizing the color, logos, and internal ads served.

Be careful when you're choosing your QUERY_STRING -- if it's too long, hard to remember, or suitably threatening, then the user may mistype the address (creating bad statistics) or else not type the QUERY_STRING at all. In a worst case scenario, they may not even make the attempt to visit. These are all bad choices:

# this one is simply too long. 
http://www.gamegrene.com/?newyorktimes-04-21 

# this one would be hard to remember or type. 
http://www.gamegrene.com/?04xlmfo3d 

# and this may worry people. 
http://www.gamegrene.com/?track=nyt

If you are advertising online, encoding query strings in anchor tags works just fine (and can be as long as you like, as it's all just one click as far as the user knows). To analyze your stats upon request, try the following Perl script.


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