preg_replace($pattern, $replacement, $content) 修饰符的奇葩作用

$str = "lin == 3615";
$pattern = "/(.*)/";
$str = preg_replace($pattern, "$1", $str);
print_r($str);

$pattern 中没有问号

结果为:lin == 3615

$str = "lin == 3615";
$pattern = "/(.*?)/";
$str = preg_replace($pattern, "$1", $str);
print_r($str);

$pattern 中有问号(相当于防止贪婪匹配)

结果为:lin == 3615

$str = "lin == 3615";
$pattern = "/(.*)/U";
$str = preg_replace($pattern, "$1", $str);
print_r($str);

$pattern 中无问号( U 防止贪婪匹配)

结果为:lin == 3615

$str = "lin == 3615";
$pattern = "/(.*?)/U";
$str = preg_replace($pattern, "$1", $str);
print_r($str);

$pattern 中有问号( U 防止贪婪匹配)，相当于失去了U的意义

<span class='fuck'>lin</span> == <span>3615</span>