打开一个nginx的网站配置：

location ~ \.php$ {
        try_files      $uri =404;
        root           /usr/share/nginx/
html
/public;
        fastcgi_pass   127.0.0.1:9000;
        fastcgi_index  index.php;
        fastcgi_param  SCRIPT_FILENAME  $document_root$fastcgi_script_name;
        fastcgi_param  CI_ENV 'development';
        include        fastcgi_params;
}

重启Nginx后在PHP中打印 print_r($_SERVER) 即可获取到此变量 CI_ENV