Can someone explain this strange mod_rewrite regex behavior - php

Question

I've been working on a script for debugging mod_rewrite, and when testing their regex system I've had some strange results. I'm wondering if this is normal behavior for the mod_rewrite regex engine or if some part in my code is causing it.
Requested URL: http://myurl.com/path/to/something
.htaccess has: RewriteRule to where
Using my debugging system, the following is what happens when that RewriteRule is used:
path/to/something -> where/to/something
Shouldn't it be path/where/something???
Here's the full .htaccess file
RewriteEngine On
RewriteBase /ModRewriteTester
RewriteRule .* - [E=ORIG:$0]
RewriteRule to where
RewriteRule .* - [E=MODD:$0]
RewriteRule .* index.php
Then I've got a php script that's reading in the environmental variables $_SERVER['REDIRECT_ORIG'] and $_SERVER['REDIRECT_MODD'], that's where I'm getting the previously stated paths.
If anyone knows a better way to explicitly show how mod_rewrite's regex engine works I'm open to it. The initial question still stands though...

Answer 1

Your rule:
RewriteRule to where
...will rewrite a URL that matches to and replace it with the URL representing what would be a request to /where. It's possible in certain circumstances for mod_rewrite to try and re-add what Apache believes to be PATH_INFO, which could create a situation like the following:
path/to/somewhere -> PATH_INFO = /to/somewhere
path/to/somewhere -> /where
(append PATH_INFO) -> /where/to/somewhere
To check if this is the case in your scenario, you can add the DPI flag to the RewriteRule to discard the PATH_INFO if it exists. This would look like this:
RewriteRule to where [DPI]
In this case, you would end up with just the URL /where. If you wanted to replace to with where while retaining the rest of the URL, you would need a rule more like this:
RewriteRule (.*?/)?to(/.*)? $1where$2
As far as debugging your rule set goes, if you have access to the Apache configuration you're much better off using the RewriteLog directive with a sufficiently high RewriteLogLevel. If you don't have access to the configuration, you're pretty much limited to doing something similar to what you're trying to do now.