Good afternoon, friends.

I need your help with something related to hosting. My client has provided a hosting service called Alkar.net, and it seems that nothing has changed in the past ten years. They still use CGI and other outdated technologies.

Recently, I encountered a problem when I was setting up a website with some rules in the .htaccess file. Suddenly, I started seeing 500 errors, which I've experienced before on hosting sites in France and Belgium. Usually, I can fix this issue by finding and correcting a rule or adding a recommended one. However, this time, I stumbled upon something that I've never encountered before.

The problematic rule itself is quite simple:

RewriteRule ^(?!admin/|css/|images/|inc/|js/|m/|pma/)(.+)$ index.php [L,QSA]

In other words, any URL that doesn't start with admin/, css/, images/, inc/, js/, m/, or pma/ should be redirected to index.php. This rule has been working flawlessly for the past four years, and I haven't made any changes to it. It works perfectly fine on my test hosting, but on this provider's platform, it triggers a 500 error. It seems that the issue lies with the use of "(?!)" which represents a negation of what follows.

My question to you, my dear friends, is how should I proceed? This rule is crucial for the proper functioning of the website. I appreciate any advice or suggestions you may have.

Thank you for your time and assistance.

From a high-level diagnostic standpoint, you're on the right lines—seeing the 500 error does suggest that there's something wrong with your RewriteRule syntax as interpreted by the server.

You're correct in stating that "(?!)" is a negative lookahead assertion in regex, which should exclude the directories you specified from the rewrite rule. If you're sure that this specific regex is causing the problem, it could be that the hosting environment doesn't support this particular type of regex, or perhaps has a different way of interpreting it. This is often due to differences in the version or configuration of the Apache mod_rewrite module.

As a first step on troubleshooting this, I'd recommend to create a simpler version of the rule, possible without negative lookahead for testing purposes. Something like:

RewriteRule ^admin/. /index.php [L,QSA]
RewriteRule ^css/. /index.php [L,QSA]
RewriteRule ^images/. /index.php [L,QSA]
...
That checks the directories individually, but with the same rewrite rule applied. If these rules work without issues, then it's likely that the "(?!)" part of your original rule is indeed the problem.

In this case, you might need to seek workaround without using negative lookahead. Something based on the principle of setting a condition that directories we want to exclude should not be rewritten and then a rule that rewrites everything else:

RewriteCond %{REQUEST_URI} !^/admin/
RewriteCond %{REQUEST_URI} !^/css/
RewriteCond %{REQUEST_URI} !^/images/
...
RewriteRule ^(.*)$ /index.php [L,QSA]
This explicitly states "do not rewrite URLs that match /admin/ etc. to index.php" before rewriting all (^(.*)$) other URLs. It's a bit tedious and verbose, but usually works in environments that don't support negative lookahead assertions.

Remember to modify paths if your .htaccess file isn't in the root directory, and always double-check your file syntax as even small errors can cause issues.


If the above suggestions don't work, you could have a compatibility issue, or there could be another directive elsewhere in your .htaccess file or server configuration that's causing problems in combination with this rule.

Check for other entries in your .htaccess file that might be causing conflicts. Often, issues can be caused by directives placed earlier in the .htaccess file, which affect how later directives are interpreted.

Double-check that the mod_rewrite module is actually enabled on the server. Often the hosting provider can help with this. Note that your rule will also be ignored if your .htaccess files aren't being read at all due to the server configuration. In such circumstances, you might see errors even when there's nothing wrong with the rules themselves.

An additional debugging approach is to enable detailed logging for the rewrite engine. That can also provide crucial insights. You would add these lines to your main server config (not the .htaccess file):

RewriteLog "/path/to/rewrite.log"
RewriteLogLevel 9
However, these directives will not work on Apache 2.4 and higher. For Apache 2.4 and higher, you can use the following directives in your main server config:

LogLevel alert rewrite:trace6
This will log rewrites to your server error log. Be sure to turn off this intensive logging when you're done!


There are a few additional steps you can take.

Confirm hosting environment: Detailed information about your hosting environment might be needed to solve this issue. This includes the Apache version, PHP version, enabled Apache modules, etc. This information will help you identify any incompatibilities or specific quirks.

Contact technical support: If the provider is enforcing certain limitations or settings, contacting their support might provide more clarity. Assuming you haven't done this already, it might be worthwhile to reach out to Alkar.net's customer support to explain the issue and inquire about any known issues, changes or limitations with their regex handling.

Alternative ways for URL redirection: If the problem can't be solved on the hosting provider's side, you could look into handling the URL redirection through PHP or another server-side scripting language, rather than relying on .htaccess. This is more of a workaround than a solution but could keep things moving in the meantime.

Here is how you might handle it on PHP:

<?php
    $request = $_SERVER['REQUEST_URI'];

    if (!preg_match("#^(admin/|css/|images/|inc/|js/|m/|pma/)#", $request)) {
        include('index.php');
        exit();
    }

    // rest of your code here.
?>
Please note that this is a very simplified version and would likely require additional logic to handle the existing scripts from your old index.php file.

Unfortunately, there's only so much you can do if your hosting provider has specific limitations or bugs. If this issue continues and it's not feasible to switch to another provider, you might need to re-code the website to work within the limitations imposed by their system. Consult with your team or client to evaluate the most efficient path forward.

If you are still interested, you should know that Apache versions up to 2.0 do not support PCRE, but only support POSIX regular expressions (http://httpd.apache.org/docs/2.0/new_features_2_0.html ). This means that the negative statement (?! this is a PCRE feature, not POSIX regular expressions), which is why it doesn't work. According to Apache, it's not possible to compile this regular expression.

However, there is a solution. You can replace your string with the following code, and it will work on the old Apache version as well (tested):

RewriteEngine on
RewriteBase /
RewriteCond %{REQUEST_URI} !^/admin/.*
RewriteCond %{REQUEST_URI} !^/css/.*
RewriteCond %{REQUEST_URI} !^/images/.*
RewriteCond %{REQUEST_URI} !^/inc/.*
RewriteCond %{REQUEST_URI} !^/js/.*
RewriteCond %{REQUEST_URI} !^/m/.*
RewriteCond %{REQUEST_URI} !^/pma/.*
RewriteRule ^(.*) /index.php [L,QSA]

The above code should be used if index.php is located in the root. If it is not, make sure to change the RewriteBase and the path to index.php in every condition where it says !^/admin/.*.

Consider utilising the RewriteCond directive to exclude directories. It leverages the PCRE format for regular expressions, which may be triggering your issue.

It's useful to remember that regular expressions can be highly effective but also extraordinarily complex in certain contexts. Ensure you have an essential understanding to avoid any unintended fallout.

For instance, your directive could be revised as follows:

RewriteCond %{REQUEST_URI} !^/(admin/|css/|images/|inc/|js/|m/|pma/).*
RewriteRule ^(.*)$ index.php [L,QSA]

In this example, if the requested URI doesn't match any of the specified folders (admin, css, images, inc, js, m, pma), it will be rewritten to 'index.php'.

This approach gives you the flexibility to exclude specific directories from being rewritten, thereby simplifying overall website navigation. Experimentation, patience, and learning are key to mastering Apache's mod_rewrite rules!