Help With Nginx Directives

I am using a custom php framework that utilizes the following rewrite rules:

RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-l
RewriteRule ^(.+)$ index.php?url=$1 [QSA,L]

In the Nginx Directive under the domain's option tab, I've tried adding

location / {
if (!-e $request_filename){
rewrite ^(.+)$ /index.php?url=$1 last;
}
}

and I've also tried adding

location / {
try_files $uri $uri/ /index.php?url=$1 last;
}

and none of the options I've tried seem to work. I visit the site and it want to download instead of serve the index.php file. First, did I put them in the right place, and second, did I convert it correctly? Any help with this is greatly appreciated.

 

Try

Code:

location / {
  try_files $uri $uri/ /index.php?url=$request_uri&$args last;
}

 

Thanks Falko for responding. I've added it to the directives, but it is giving me a 404. Here are some examples of what the urls may look like and what works or doesn't work with the rewrite you suggested:

http://example.com/dashboard/ => 404 Error
http://example.com/profile/ => 404 Error
http://example.com/index/logout/ => 404 Error
http://example.com/course/?id=1&term=13/FA => 404 Error
http://example.com/course/student/schedule/?term=13/FA => 404 Error

If I add this to the directive:
location / {
try_files $uri $uri/ @rewrite;
}
location @rewrite {
rewrite ^/(.*)$ /index.php?url=$1;
}

I will get these results:
http://example.com/dashboard/ => Error 500
http://example.com/profile/ => Error 500
http://example.com/index/logout/ => Error 500
http://example.com/course/?id=1&term=13/FA => Works
http://example.com/course/student/schedule/?term=13/FA => Works

I am not that great at rewrite rules, so can you help me find a happy medium between our two rewrites? Thanks again for your help.

 

Actually with one small change to my rewrite, it does work.