I'm new to Nginx rewrites and looking for help in getting a working and minimal rewrite code. We would like to use urls like 'somecity.domain.com' on campaign materials and have the result go to city-specific content within the 'www' site.

So, here are use cases, if the customer enters:

www.domain.com                          (stays) www.domain.com
domain.com                              (goes to) www.domain.com
www.domain.com/someuri                  (stays the same)
somecity.domain.com                     (no uri, goes to) www.domain.com/somecity/prelaunch
somecity.domain.com/landing             (goes to)   www.domain.com/somecity/prelaunch
somecity.domain.com/anyotheruri         (goes to) www.domain.com/anyotheruri

Here's what I've come up with so far, and it partially works. What I can't understand is how to check if there is no path/uri after the host, and I'm guessing there is probably a way better way to do this.

if ($host ~* ^(.*?)\.domain\.com)
{   set $city $1;}
if ($city ~* www)
{   break; }
if ($city !~* www)
{ 
  rewrite ^/landing http://www.domain.com/$city/prelaunch/$args permanent;
  rewrite (.*) http://www.domain.com$uri$args permanent;
}