Redirect in nginx

From www.example.com to example.com

server {
         server_name     www.example.com
          return    301 $scheme://example.com$request_uri;
}

From example.com to www.example.com

server {
         server_name     example.com
          return    301 $scheme://www.example.com$request_uri;
}

-------
Some people try it in this way also, but it's a bad way of doing redirect as per nginx documentation. http://wiki.nginx.org/Pitfalls

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

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