Relative path variables in .htaccess

What happens when you point your browser directly at the http://your.site/errors/404.php url?

I suspect your paths may be a bit confused.

C.

There's a solution but it's not simple.

Use RewriteMap.

Here's how I would do:

Create a RewriteMap file. See here for more information. This is a very simple text file with: first, the wrong URL without the '/', then one space (at least) and then the right url, like this:

ok​ /folder1/
ok /folder2/
ok /folder3/

Then the code:

RewriteMap myfoldermap \
  dbm:/web/htdocs/yourwebsite.com/rewriterules/myfoldermap.map

RewriteCond %{REQUEST_URI} ^/([^/]+)/(.*)
# Now in '%1' there's the name of the folder
# Don't touch the URL but...
# ...check if it exists in the map file
RewriteRule (.*) - [QSA,E=FOLDERMAP:${myfoldermap:%1|notfound}]

# if the environment is neither empty or not found...
RewriteCond %{E:FOLDERMAP} !^(notfound|)$
# this means we found something...
# => apply the RewriteRule
RewriteRule ^(.*)$ router.php [L,QSA]

If it doesn't work: read my usual "two hints", and add the rewrite log in your question.

Two hints:

If you're not in a hosted environment (= if it's your own server and you can modify the virtual hosts, not only the .htaccess files), try to use the RewriteLog directive: it helps you to track down such problems:

# Trace:
# (!) file gets big quickly, remove in prod environments:
RewriteLog "/web/logs/mywebsite.rewrite.log"
RewriteLogLevel 9
RewriteEngine On

My favorite tool to check for regexp:

http://www.quanetic.com/Regex (don't forget to choose ereg(POSIX) instead of preg(PCRE)!)