I have been trying to convert the following htaccess rules to nginx with no
luck.

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

I've tried:

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

and I've also tried:

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

None seem to work. Any help with this is greatly appreciated.