Non-www to www and vice versa

How can I rewrite nginx to redirect non-www to www and vice versa?

I have tried the following by adding it in the nginx directives without luck.

non-www to www:

Code:

	server {
		server_name example.com;
		rewrite ^(.*) http://www.example.com$1 permanent;
	}

www to non-www:

Code:

	server {
		server_name www.example.com;
		rewrite ^(.*) http://example.com$1 permanent;
	}

 

No one knows about this?

 

www to non-www:

Code:

if ($http_host != "example.com") {
  rewrite ^ $scheme://example.com$request_uri? permanent;
}

non-www to www:

Code:

if ($http_host != "www.example.com") {
  rewrite ^ $scheme://www.example.com$request_uri? permanent;
}

 

Cheers!

Thank you very much.

 

Even putting this code in [nginx directives], it continues appearing 2 urls.
The strange thing is that
in the url with www: the apache page appears
and in the url without www the ispconfig page.