正方括號後面的正則表達式管道

Question

我發現了一個我完全不理解的正則表達式。

它看起來像這樣：

([|)\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(]|) 

我也明白，它試圖匹配對一些喜歡255.255數字，它應該是一個完整的詞。

但是什麼是「（[|）」「（] |）」？方括號和最後一箇中的管道看起來也是錯誤的順序。

Answer 1

krackmoe，有趣的是，沒有([|)：這是一種錯覺。

正則表達式引擎不會看到([|)

它看到(這將打開捕獲組1，那麼它看到一個字符類[|)\b(25[0-5]不作一大堆的意義有以下幾個原因。例如，\b與文字字符「b」匹配，字符2和5與範圍0-5重複。

所以你很對不理解它。

我認爲作者想在這裏設置一個字邊界，但就目前而言，這是一個錯字。

僅供參考，這裏是對正則表達式的令牌令牌解釋。 （別擔心，我沒有輸入所有內容，它是由RegexBuddy自動生成的。）

* 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) 

Answer 2

正則表達式的目的還不清楚。 Debuggex提供了很好的可視化。

Debuggex Demo

約0〜255的部分是清楚的（000，00也接受值）。但是，嘗試匹配|)([]符號的原因不明。

我相信第一個[和最後]出現是因爲錯誤。沒有他們，內部正則表達式看起來是合理的。但(|)和\b也看起來不正確，所以我的猜測是我們也可以省略(|)。

(|)\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(|) 

Debuggex Demo