php - 这个正则表达式是什么意思？

Question

/\n\s*\n/s

我觉得是

• 换行
• 后跟0个或多个空格
• 然后换行

这个这个正确吗？如果不是，你能解释一下吗？

Answer 1

几乎正确:\s 实际上意味着“任何空白字符”，它还包括制表符和可能的 CR/LF(\r 和 \n).

如果您使用的是 perl，\s 也可能匹配其他一些字符(来自 perlre ):

If Unicode is in effect, "\s" matches also "\x{85}", "\x{2028}, and "\x{2029}"

更多说明。

• 因为匹配没有锚定(^ 在开头或 $ 在结尾)，大多数引擎将此表达式视为意味着字符串可以匹配任何位置字符串。换句话说，正则表达式 /cat/ 将匹配“cat”、“caterpillar”或“concatenate”。因此，您的字符串需要包含您所描述的内容，但可以添加任何其他内容作为前缀或后缀。
• 末尾的/s一般表示把整个字符串当成一大行。同样，来自 perlre:

Treat string as single line. That is, change "." to match any character whatsoever, even a newline, which normally it would not match.

The "/s" and "/m" modifiers both override the $* setting. That is, no matter what $* contains, "/s" without "/m" will force "^" to match only at the beginning of the string and "$" to match only at the end (or just before a newline at the end) of the string. Together, as /ms, they let the "." match any character whatsoever, while still allowing "^" and "$" to match, respectively, just after and just before newlines within the string.