DirectoryIndex app_dev.php
<IfModule mod_rewrite.c>
    RewriteEngine On
    RewriteCond %{REQUEST_URI}::$1 ^(/.+)/(.*)::\2$
    RewriteRule ^(.*) - [E=BASE:%1]
    RewriteCond %{ENV:REDIRECT_STATUS} ^$
    RewriteRule ^app_dev\.php(/(.*)|$) %{ENV:BASE}/$2 [R=301,L]
    RewriteCond %{REQUEST_FILENAME} -f
    RewriteRule .? - [L]
    RewriteRule .? %{ENV:BASE}/app_dev.php [L]
</IfModule>

<IfModule !mod_rewrite.c>
    <IfModule mod_alias.c>
        RedirectMatch 302 ^/$ /app_dev.php/
    </IfModule>
</IfModule>