PHP 正则表达式匹配行尾的差异

Question

给定代码：

$my_str = '
Rollo is*
My dog*
And he\'s very*
Lovely*
';

preg_match_all('/\S+(?=\*$)/m', $my_str, $end_words);
print_r($end_words);

在 PHP 7.3.2 (XAMPP) 中我得到了意外的输出

Array ( [0] => Array ( ) )

而在 PhpFiddle 中，在 PHP 7.0.33 上，我得到了预期的结果：

Array ( [0] => Array ( [0] => is [1] => dog [2] => very [3] => Lovely ) )

为什么我会得到这种差异？ 7.0.33 之后正则表达式的行为有什么变化吗？

Answer 1

看来在你的环境下，PCRE库编译时没有带PCRE_NEWLINE_ANY选项，多行模式下的$只匹配LF符号和. 匹配除 LF 以外的任何符号。

您可以使用 PCRE (*ANYCRLF) 动词修复它：

'~(*ANYCRLF)\S+(?=\*$)~m'

(*ANYCRLF) 指定换行符约定：(*CR)、(*LF) 或 (*CRLF) 等同于 PCRE_NEWLINE_ANY 选项。见 PCRE documentation:

PCRE_NEWLINE_ANY specifies that any Unicode newline sequence should be recognized.

最后，这个 PCRE 动词使 . 可以匹配任何字符但是 CR 和 LF 符号和 $ 将匹配任何一个字符之前这两个字符。

在 rexegg.com 查看更多关于这个和其他动词的信息：

By default, when PCRE is compiled, you tell it what to consider to be a line break when encountering a . (as the dot it doesn't match line breaks unless in dotall mode), as well the ^ and $ anchors' behavior in multiline mode. You can override this default with the following modifiers:

✽ (*CR) Only a carriage return is considered to be a line break
✽ (*LF) Only a line feed is considered to be a line break (as on Unix)
✽ (*CRLF) Only a carriage return followed by a line feed is considered to be a line break (as on Windows)
✽ (*ANYCRLF) Any of the above three is considered to be a line break
✽ (*ANY) Any Unicode newline sequence is considered to be a line break

For instance, (*CR)\w+.\w+ matches Line1\nLine2 because the dot is able to match the \n, which is not considered to be a line break. See the demo.

PHP 正则表达式匹配行尾的差异

Difference in matching end of line with PHP regex

php

regex

php-7

php-7.3