Obviously, so that I could post here i replaced the $ with % and part of the URLs with xx's. I am just picking a random number (1 or 2), then redirecting based on whichever number is picked.

Thats the easier way to do it, but it won't be exactly 50% because it's random. If you need a perfect 50/50 split, you'll need to make a counter (store that info in a database).

rand(1,2) will work fine...
Over time it will it will average out very close to 50/50.

You could also keep track of a counter in a file. Read the number, and if ($num mod 2 == 0) goto offer 1, otherwise to offer 2. Before you redirect, increment $num and write it back out to the file. If you have more than two offers, this logic needs to be adjusted though... Good luck.

Just use 1 flag in a file.

Read the file contents......

If 1 then redirect to site one and write 2 to the file.
If 2 then redirect to site two and write 1 to the file.

Tick tock tick tock..... see saw

Hi Brandon,

Using the random functions aren't great. I generate test data for applications and I recently did one where I had the system enter 5000 people into a database with ages between 16 and 50. You would be surprised how many times the number 43 came up. Sometimes back to back.

But Nick has it down pat. This can be solved with a simple flag (or sentinel). File is the way to go. Database connects are long and expensive and if the database goes down you show neither page.

Here's a solution which I learned about many years ago from the book "Web Application Development with PHP 4.0." It uses a technique called polymorphism, or self modifying code. This isn't strictly necessary as you could use a separate file, but I present it here because I find it interesting.

<?php
$counter = 0;
/* Don't modify above this line */

$URL_ARRAY = array(
0 => 'http://someurl1',
1 => 'http://someurl2'
);

// if counter is 0 above, then set it to 1 for next time
// otherwise if any other number, set back to 0
if ($counter == 0)
{
$new_counter = 1;
}
else
{
$new_counter = 0;
}

// write the new value of $counter to this file
$file = fopen(basename($PHP_SELF), "r+");
fputs($file, "<?php\n\$counter = $new_counter;");

// perform your redirect using orig value of $counter
header('Location: ' . $URL_ARRAY[$counter]);

?>

There you go. Untested but give it a try. It also gives you the ability to add more urls or change the logic if you like. In short this script does:

- sets the counter for this session (0 or 1)
- assigns your URLs to an array
- sets the new counter for next session (1 or 0)
- writes the new counter back to the same file for next time
- performs the redirect using the original value of counter

Hope this helps.

Hi Brandon,

The file you are trying to write cannot be written by your webserver because it doesn't have permission. You created it as your shell account user (you) but the webserver runs under a different account and is prevented from changing your file.

If you are using Linux, change the permissions like this:

chmod 0666 filename.php

And replace filename with the actual name of your script. Hope that helps.

Take a look at post #7.

In line 2 there is a variable assignament that reads:

$counter = 0;

But in your replay to me it looks like most of the variable names are gone. Take a look at your reply in post #8 and you'll see they are ALL missing for some reason. Line 2 there just reads:

=0;

Odd. Try copying from post #7 again.

Great! Glad it works as prescribed, and glad I could help.

Enjoy!

A word of caution when using a file. If two visitors hit your site at nearly the same time, two processes can end up writing to the file at the same time, and you might get unexpected results. This is actually a harder problem to solve using a file than appears at first blush.

Yes, file locking can be an issue. But given the circumstances it is probably better than the other options. A database connect is too expensive and must be performed on each page load. rand() functions have no way of splitting results evenly, especially with only two values. SQLlite is an option if installed with PHP.

You can put in logic to see if the file is available for writing and so forth. flock() would make sure the file is locked, but it doesn't work on an NFS system like most hosts use. Anyone trying to refresh a file edited over NFS may have run into the kinds of problems this presents.

Ultimately if I knew the shared memory functions were available on a system I would write a single bit flag into memory and use that. But the solution above would suffice most situations unless you were getting multiple connections per microsecond regularly.