Subdomain Proxy/Rewrite with Nginx Proxy

I want to take m.example.com and direct those requests to example.com/mobile/ with nginx. (The same nginx sever will be serving example.com)

Can someone help me with the config I would need? I can post my nginx.conf if needed, but I assume its something like:

location / {
rewrite /([^/] +) /mobile/$1 break;
proxy_pass http://127.0.0.1;

}

Am I in the right ballpark?