htaccess Multiple Rewrite issues - php

Question

I'm new to htaccess so this may be easy to many here, but it's eluding me. I have two folders, one is "public" and the other is "admin". The htaccess code was pieced together from elsewhere but it's not properly working for me.
If www.domain.com/admin, then send it to admin/index.php
If www.domain.com/[anything else], send to public/index.php?xxx
If www.domain.com then send to pubic/index.php
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteRule ^admin /admin/index.php [QSA,L]
RewriteRule ^$ public/ [L]
RewriteRule (.*) public/$1 [L]
</IfModule>
This is the htaccess file in the public folder. I do not have an htaccess file in the admin folder.
<IfModule mod_rewrite.c>
Options -Multiviews
RewriteEngine On
RewriteBase /public
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^(.+)$ index.php?url=$1 [QSA,L]
</IfModule>
Problems:
www.domain.com/admin generates a 500 Internal Server Error
www.domain.com/anything also generate a 500 error
www.domain.com works as expected
Thanks a bunch for any help!

Answer 1

Use only a single set of rules, do not spread them over several places, that only makes things more complex and error prone. If possible use the real http server configuration instead of dynamic configuration files, more on that below.
RewriteEngine On
RewriteRule ^/?admin/ /admin/index.php [END]
RewriteCond %{REQUEST_URI} ^/public/index\.php$
RewriteRule ^ /public/%{QUERY_STRING} [R=301]
RewriteCond %{REQUEST_URI} ^/public/(.*)$
RewriteRule ^ /public/%1 [R=301]
RewriteRule ^/?(.*)$ public/index.php?$1 [END]
It is a good idea to start out with a 302 temporary redirection and only change that to a 301 permanent redirection later, once you are certain everything is correctly set up. That prevents caching issues while trying things out...
In case you receive an internal server error (http status 500) using the rule above then chances are that you operate a very old version of the apache http server. You will see a definite hint to an unsupported [END] flag in your http servers error log file in that case. You can either try to upgrade or use the older [L] flag, it probably will work the same in this situation, though that depends a bit on your setup.
This implementation will work likewise in the http servers host configuration or inside a dynamic configuration file (".htaccess" file). Obviously the rewriting module needs to be loaded inside the http server and enabled in the http host. In case you use a dynamic configuration file you need to take care that it's interpretation is enabled at all in the host configuration and that it is located in the host's DOCUMENT_ROOT folder.
And a general remark: you should always prefer to place such rules in the http servers host configuration instead of using dynamic configuration files (".htaccess"). Those dynamic configuration files add complexity, are often a cause of unexpected behavior, hard to debug and they really slow down the http server. They are only provided as a last option for situations where you do not have access to the real http servers host configuration (read: really cheap service providers) or for applications insisting on writing their own rules (which is an obvious security nightmare).