递归正则表达式不匹配模板块 [英] Recursive regex not matching template blocks

问题描述

我试图更多地了解正则表达式，在这种情况下，您可以在正则表达式中进行递归.

I'm trying to understand more about regex and in this case the recursion you can do in a regular expression.

我正在尝试匹配 {foreach $VAR} ... {/foreach} 的嵌套块.但由于某种原因，我的正则表达式不匹配，我不明白为什么.

I'm trying to match a nested block of {foreach $VAR} ... {/foreach}. But for some reason my regex isn't matching and i don't understand why.

我希望这里的任何人都可以对此有所了解.我对快速正则表达式修复不感兴趣.但实际上更多的是为什么我的正则表达式没有按照我的预期做.究竟发生了什么?

I was hoping anyone here could shed some light on it. I'm not interested in a quick regex fix. But really more as why my regex isn't doing what i expect. What exactly is happening?

这是我的代码:

<?php
$str = 'start of text
{foreach $ABC}
  in 1st loop
  {foreach $XYZ}
    in 2nd loop
  {/foreach}
{/foreach}
some other stuff';

if ( preg_match ( '#{foreach \$.*?}((?!foreach)|(?R))*{/foreach}#', $str, $matches ) )
{
    print_r($matches);
}
else
{
    echo 'No match';
}

这是我的正则表达式的细分，我认为它是如何工作的:

Here is the breakdown of my regex as how i think it's wokring:

{foreach \$     #match literally "{foreach $"
.*?}            #followed by any character ending with a '}'
(               # start a group
  (?!foreach)   # match any character, aslong as it's not the sequence 'foreach'
  |             # otherwise
  (?R)          # do a recursion
)               # end of group
*               # match 0 or more times with a backtrace...
{/foreach}      # ...backtracing until you find the last {/foreach}

这就是我认为正则表达式的工作方式.但显然情况并非如此.所以我的问题是，我的解释哪里错了?

That's how i think the regex works. But obviously that is not the case. So my question is, where am i wrong in my explanation?

您可以在此处使用此代码:http://codepad.viper-7.com/508V9w

You can play around with this code here: http://codepad.viper-7.com/508V9w

只是为了澄清.

我正在尝试获取每个 foreach 块的内容.所以就我而言:

I'm trying to get the contents of each foreach block. So in my case:

arr[0] => in 1st loop
      {foreach $XYZ}
        in 2nd loop
      {/foreach}
arr[1] => in 2nd loop

或 -

arr[0] => {foreach $ABC}
      in 1st loop
      {foreach $XYZ}
        in 2nd loop
      {/foreach}
    {/foreach}
arr[1] => {foreach $XYZ}
        in 2nd loop
      {/foreach}

哪个都行.

推荐答案

首先，. 确实匹配除 换行符以外的任何东西.为了让它也匹配换行符，你必须设置修饰符 s.

First of all, the . does match anything but newlines per default. To have it match newlines as well, you have to set the modifier s.

其次，您在此处使用断言:((?!foreach)|(?R))*，但没有要匹配的实际字符.在 * 量词或其他东西之前至少需要一个点.

And secondly, you are using assertions here: ((?!foreach)|(?R))*, but no actual characters to match. You need at least a dot before the * quantifier or something.

#{foreach \$.*?}((?!foreach)|(?R)).*{/foreach}#s 为您的测试文本提供以下结果:

#{foreach \$.*?}((?!foreach)|(?R)).*{/foreach}#s gives the following result with your test text:

Array
(
    [0] => {foreach $ABC}
  in 1st loop
  {foreach $XYZ}
    in 2nd loop
  {/foreach}
{/foreach}
    [1] => 
)

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