正则表达式：计算字符数
我正在编写一个 PHP 脚本，用于搜索 dokuWiki 文档中的特定标题。
我当前的模式如下所示：
$pattern = "/.*=+ ". $header ." =+([^=]+)/m";
preg_match($pattern, $art->text, $m);
if (!empty($m[1])) {
$art->text = $m[1];
} else {
$art->text = "";
}
示例文档：
====== TestHeader ======
Testtext
===== Header2 =====
Testtext2
==== Header3 ====
Testtext3
====== Header4 ======
Testtext4
当搜索 TestHeader 时，我的结果是：
====== TestHeader ======
Testtext
我希望该模式返回：
====== TestHeader ======
Testtext
===== Header2 =====
Testtext2
==== Header3 ====
Testtext3
或者换句话说：我想匹配由 less = 包围的所有标头，然后我正在寻找的标题。
正则表达式可以实现这样的功能吗？
提前致谢！
I'm writing a PHP-Script which searches for particular headlines inside a dokuWiki-document.
My current pattern looks like this:
$pattern = "/.*=+ ". $header ." =+([^=]+)/m";
preg_match($pattern, $art->text, $m);
if (!empty($m[1])) {
$art->text = $m[1];
} else {
$art->text = "";
}
A sample document:
====== TestHeader ======
Testtext
===== Header2 =====
Testtext2
==== Header3 ====
Testtext3
====== Header4 ======
Testtext4
When searching for TestHeader my result AS-IS is:
====== TestHeader ======
Testtext
I would wish that the pattern returns:
====== TestHeader ======
Testtext
===== Header2 =====
Testtext2
==== Header3 ====
Testtext3
Or in other words: I would like to match all headers which are surrounded by less = then the header I was searching for.
Is something like this possible with regular expressions?
Thanks in advance!
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因为我不是一个优秀的 PHP 编码员，所以我不知道是否有任何特殊的 PHP 扩展可以满足您想要的“正常”正则表达式。除此之外，正则表达式不可能解决您的问题。
如果您感兴趣的话，这背后有一些信息理论：正则表达式只能分析所谓的“常规语言”（请参阅相应的 维基百科文章）。无需过多深入理论，我就可以告诉您正则表达式无法“计算”事物的直觉（至少不是在它们可以比较匹配中的两个计数的意义上）。
重述 WP 示例：无论 N 是什么，您都找不到包含 N a 后跟 N b 的字符串。
当然，这并不是数学证明您所寻找的东西是不可能的，但它应该让您了解正则表达式可以做什么和不能做什么。华泰
As I'm not a great PHP coder I don't know if there are any special PHP extensions to "normal" regexp's that allow for what you want. Other than that, regexps can't possibly solve your problem.
There is some information theory behind that, in case you are interested: regexps can only analyse so called "regular languages" (see the corresponding Wikipedia article). Without diving into theory too much, I can give you the intuition that regular expressions can't "count" things (at least not in the sense that they can compare two counts within the match).
To restate the WP example: you can't find a string that has N a's followed by N b's no matter what N is.
Of course this is no mathematical proof that what you look for isn't possible, but it should give you a feeling about what regular expressions can and can't do. HTH
您可以通过几个步骤完成此操作：
假设您知道要在标头中查找 $n 或更少 = 字符：
虽然您必须使用两个正则表达式并进行一些处理，但它应该很快，第二个正则表达式将完全满足您的要求。
You can do it in a couple steps:
Suppose you knew you were looking for $n or fewer = characters in the header:
Although you'd have to use two regular expressions and do a little processing, it should be pretty quick, and the second regular expression would do exactly what you're asking for.