问如何在多域环境下将nginx中的非www重定向到www

EN

In curl -I http://example.com 

curl: (6) Could not resolve host http://example.com

blank    IP
mail     IP
www      IP

server {
        listen 80;
        listen [::]:80;
        server_name example.com www.example.com; 
        access_log /var/log/nginx/example.com.log;
        error_log /var/log/nginx/example.com-error error;

        root /var/www/examplecom/public;
        index index.html index.php;

        location ~ \.php?$ {
            try_files $uri =404;
            include fastcgi_params;
            fastcgi_pass unix:/var/run/php-main.socket;
            fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
            fastcgi_intercept_errors on;
            fastcgi_split_path_info ^(.+\.php)(.*)$;
            #Prevent version info leakage
            fastcgi_hide_header X-Powered-By;
        }
}

server {
    listen 80;
    server_name example.com;
    return 301 $scheme://www.example.com$request_uri;
}