如何获取 PHP exec() 错误响应?

如何获取 PHP exec() 错误响应?

　　

 ob_start();
 exec($cmd . " 2>&1", $output);
 $result = ob_get_contents();
 ob_end_clean();
 var_dump($output);

　　

https://stackoverflow.com/questions/345794/how-to-retrieve-php-exec-error-responses