方括号后的Regex管

Question

我找到了一个我很不明白的正则表达式。

它看起来像这样：

([|)\b(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\b(]|)

我确实知道它试图与255.255等一些数字匹配，并且它应该是一个完整的单词。

但是“([|)”(]|)”是干什么用的呢？最后一个中的方括号和管道的顺序看起来也是错误的。

Answer 1

正则表达式的用途尚不清楚。Debugex的可视化效果很好。

调试演示

关于0~255的部分是清楚的（000、00也是可接受的值）。但是尝试匹配|)([]符号有未知的原因。

我认为第一个< code>[和最后一个< code>]出现是因为错误。没有它们，内部正则表达式看起来很合理。但是< code>(|)和< code>\b看起来也不对，所以我的猜测是我们也可以省略< code>(|)。

(|)\b(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\b(|)

调试演示

Answer 2

Krackmoe，有趣的是，没有（[|）：这是一种视错觉。

正则表达式引擎看不到([|)

它会看到< code>(，这会打开捕获组1，然后它会看到一个字符类< code>[|)\b(25[0-5]，由于几个原因，这个字符类没有多大意义。例如，< code>\b匹配文字字符“b”，字符2和5对于范围< code>0-5是多余的。

所以你不理解它是完全正确的。

我猜作者想在那里加上一个单词边界，但就目前而言，这是一个错别字。

作为参考，这里是正则表达式的逐令牌解释。（别担心，我没有输入所有这些，它是由RegexBuddy自动生成的。）

* Match the regex below and capture its match into backreference number 1 `([|)\b(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)`
    * Match this alternative (attempting the next alternative only if this one fails) `[|)\b(25[0-5]`
        * Match a single character present in the list below `[|)\b(25[0-5]`
            * A single character from the list “|)” `|)`
            * The character `\b`
            * A single character from the list “(25[” `(25[`
            * A character in the range between “0” and “5” `0-5`
    * Or match this alternative (attempting the next alternative only if this one fails) `2[0-4][0-9]`
        * Match the character “2” literally `2`
        * Match a single character in the range between “0” and “4” `[0-4]`
        * Match a single character in the range between “0” and “9” `[0-9]`
    * Or match this alternative (the entire group fails if this one fails to match) `[01]?[0-9][0-9]?`
        * Match a single character from the list “01” `[01]?`
            * Between zero and one times, as many times as possible, giving back as needed (greedy) `?`
        * Match a single character in the range between “0” and “9” `[0-9]`
        * Match a single character in the range between “0” and “9” `[0-9]?`
            * Between zero and one times, as many times as possible, giving back as needed (greedy) `?`
* Match the character “.” literally `\.`
* Match the regex below and capture its match into backreference number 2 `(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)`
    * Match this alternative (attempting the next alternative only if this one fails) `25[0-5]`
        * Match the character string “25” literally `25`
        * Match a single character in the range between “0” and “5” `[0-5]`
    * Or match this alternative (attempting the next alternative only if this one fails) `2[0-4][0-9]`
        * Match the character “2” literally `2`
        * Match a single character in the range between “0” and “4” `[0-4]`
        * Match a single character in the range between “0” and “9” `[0-9]`
    * Or match this alternative (the entire group fails if this one fails to match) `[01]?[0-9][0-9]?`
        * Match a single character from the list “01” `[01]?`
            * Between zero and one times, as many times as possible, giving back as needed (greedy) `?`
        * Match a single character in the range between “0” and “9” `[0-9]`
        * Match a single character in the range between “0” and “9” `[0-9]?`
            * Between zero and one times, as many times as possible, giving back as needed (greedy) `?`
* Assert position at a word boundary (position preceded or followed—but not both—by a Unicode letter, digit, or underscore) `\b`
* Match the regex below and capture its match into backreference number 3 `(]|)`
    * Match this alternative (attempting the next alternative only if this one fails) `]`
        * Match the character “]” literally `]`
    * Or match this alternative (the entire group fails if this one fails to match)