在正则表达式中使用 Lookahead 和 Lookbehind 忽略 BBCode 之间任意位置的单词 [英] Using Lookahead and Lookbehind in regex to ignore a word anywhere between a BBCode

问题描述

我希望在此处扩展特定代码:

I'm looking to expand on a particular code here:

/(?<![@#]|(\[img\]))\b(".str_replace(" ", "[\-_ ]", $key).")(?!\[\/img\])\b/i

目前，它检测 @ 或 # 是否直接在有问题的 $key 后面(这很好)，或者 >[img] 或 [/img] 直接在 $key 之前/之后(有问题).我想添加一个通配符，以便 [img] 和 [/img] 之间的 $key ANYWHERE 不会被替换，同时仍然保持 @ 或 # 必须仍然直接位于 $key 后面的事实.我知道在后视中不允许使用通配符.

Currently, it detects whether @ or # is directly behind the $key in question (which is fine), OR whether [img] or [/img] is directly before/after the $key (a problem). I want to add a wildcard so that the $key ANYWHERE in between [img] and [/img] will not be replaced, while still keeping the fact that @ or # must still be directly behind the $key. I am aware that wildcards are not allowed in lookbehind.

这可能吗?

我有点误解了我自己的代码.我意识到即使 [img] 不在单词前面，[/img] 仍然会触发，从而允许 @BLUE[/img]> 不触发.我希望将 #/@ 和 [img][/img] 之间的情况分开.这方面的帮助也将大有帮助.

I misinterpreted my own code a bit. I realized that [/img] will still trigger even if [img] doesn't precede the word, thus allowing @BLUE[/img] to not trigger. I wish to separate the cases between #/@ and [img][/img]. Assistance on this will greatly help as well.

基本上，[img] 和 [/img] 中的所有内容都会忽略 $key 的 preg_replace、@$key 和 #$key.然而，即使作为独立的 @$key 和 #$key(没有 [img] 标签)，$key 不应更换.

Basically, everything within [img] and [/img] will ignore preg_replace of the $key, @$key, and #$key. However, even as a standalone @$key and #$key (without [img] tags), $key should not be replaced.

推荐答案

使用环视并不是一个好方法，因为你不能使用可变长度的环视.

Using lookarounds is not a good way to do that since you can't use a variable length lookbehind.

目标是跳过 [img] 标签之间的内容，让我们看看:

The goal is to skip content between [img] tags, lets see a way:

$result = preg_replace('~\[(img|url)].*?\[/\1](*SKIP)(*FAIL)|(?<![@#])\bHELLO\b~s',
                       'GOODBYE', $str);

(*SKIP) 禁止在右侧子模式失败的情况下重试左侧已匹配的字符串部分.

(*SKIP) forbids to retry the part of the string that has been matched on the left if the subpattern fails on the right.

(*FAIL) 强制模式失败.

因为 [img] 标签总是首先被模式的第一个分支尝试，所以模式的第二个分支总是匹配 [img] 之外的字符串部分代码>标签.

Since [img] tags are always tried first by the first branch of the pattern, the second branch of the pattern matches always parts of the string that are outside [img] tags.

另一种方式

您可以将您搜索的关键字描述为前面有几个[img]..[/img] 和其他不是[img] 的字符的词标签或关键词:

you can describe the key you search as a word that is preceded by several [img]..[/img] and other characters that are not [img] tags or the key word:

$pattern = <<<'LOD'
~
(?>                      # atomic group: all possible content before "HELLO"
    (?>                      # other characters
        [^[H]++                  # all characters except [ and H
      |                        # OR
        \[(?!img]|url])          # a [ not followed by img or url
      |                        # OR
        \BH                      # an H not preceded by a word boundary
      |                        # OR
        H(?!ELLO\b)              # an H not followed by ELLO and a word boundary
    )+
  |                        # OR
    \[(img|url)].*?\[/\1]    # img or url tags
)*
\K                       # resets all from the match result
(?<![@#])HELLO
~sx
LOD;

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