Regular expression - php regular replacement of the content in src

$url = '<img src="http://img.baidu.com/upload/2312312.jpg">cccvsdvdsv<img src="http://www.sina.com/upload/434dfe2 .jpg">';

should be replaced with
$url = '<img src="/upload/2312312.jpg">cccvsdvdsv<img src="/upload/434dfe2.jpg">';
replace the domain name Remove

Reply content:

$url = '<img src="http://img.baidu.com/upload/2312312.jpg">cccvsdvdsv<img src="http://www.sina.com/upload/434dfe2 .jpg">';

should be replaced with
$url = '<img src="/upload/2312312.jpg">cccvsdvdsv<img src="/upload/434dfe2.jpg">';
replace the domain name Remove

$url = '<img src="http://img.baidu.com/upload/2312312.jpg">cccvsdvdsv<img src="http://www.sina.com/upload/434dfe2.jpg">';

echo preg_replace('/src=\"(http:\/\/.*)\//U', 'src="/', $url);