Nginx config to route domain and subdomains, except for explicit virtual hosts, to the www subdomain.

nginx_subdomain.conf

http {

  # Default virtual host for www.example.com. This will pick up all HTTP
  # requests to port 80 that are not for one of the other virtual hosts.
  server {
    listen 80;
    server_name www.example.com;

    # ...your server config here...

    if ($host != 'www.example.com') {
      rewrite ^ http://www.example.com$request_uri? permanent;
    }

    location / {
      # ...your own config here...
    }
  }

  # Virtual host for test.example.com.
  server {
    listen 80;
    server_name test.example.com;

    # ...your server config here...
  }

  # Virtual host for staging.example.com.
  server {
    listen 80;
    server_name staging.example.com;

    # ...your server config here...
  }
}

i notice that there's no root statement...?