如何进行平衡组捕获？

Question

假设我有这个文本输入.

 tes{}tR{R{abc}aD{mnoR{xyz}}}

我想提取ff输出:

 R{abc}
 R{xyz}
 D{mnoR{xyz}}
 R{R{abc}aD{mnoR{xyz}}}

目前,我只能使用msdn中的平衡组方法提取{}组内的内容.这是模式:

 ^[^{}]*(((?'Open'{)[^{}]*)+((?'Target-Open'})[^{}]*)+)*(?(Open)(?!))$

有谁知道如何在输出中包含R {}和D {}？

Answer 1

我认为这里需要一种不同的方法。一旦您匹配第一个较大的组R{R{abc}aD{mnoR{xyz}}}（请参阅我对可能的拼写错误的评论），您将无法获取其中的子组，因为正则表达式不允许您捕获各个R{ ... }组。

因此，必须有某种方法来捕获而不是消耗，而显而易见的方法就是使用积极的前瞻。从那里，您可以放置​​您使用的表达式，尽管需要进行一些更改以适应焦点的新变化，我想出了：

(?=([A-Z](?:(?:(?'O'{)[^{}]*)+(?:(?'-O'})[^{}]*?)+)+(?(O)(?!))))

[我还将“Open”重命名为“O”，并删除了右大括号的命名捕获，以使其更短并避免比赛中出现噪音]

在 regexhero.net（迄今为止我所知道的唯一免费的 .NET 正则表达式测试器）上，我得到了以下捕获组：

1: R{R{abc}aD{mnoR{xyz}}}
1: R{abc}
1: D{mnoR{xyz}}
1: R{xyz}

正则表达式的细分：

(?=                         # Opening positive lookahead
    ([A-Z]                  # Opening capture group and any uppercase letter (to match R & D)
        (?:                 # First non-capture group opening
            (?:             # Second non-capture group opening
                (?'O'{)     # Get the named opening brace
                [^{}]*      # Any non-brace
            )+              # Close of second non-capture group and repeat over as many times as necessary
            (?:             # Third non-capture group opening
                (?'-O'})    # Removal of named opening brace when encountered
                [^{}]*?     # Any other non-brace characters in case there are more nested braces
            )+              # Close of third non-capture group and repeat over as many times as necessary
        )+                  # Close of first non-capture group and repeat as many times as necessary for multiple side by side nested braces
        (?(O)(?!))          # Condition to prevent unbalanced braces
    )                       # Close capture group
)                           # Close positive lookahead

以下内容在 C# 中不起作用

我实际上想尝试一下它应该如何在 PCRE 引擎上工作，因为可以选择使用递归正则表达式，并且我认为它更容易，因为我更熟悉它并且产生了更短的正则表达式:)

(?=([A-Z]{(?:[^{}]|(?1))+}))

正则表达式101演示

(?=                    # Opening positive lookahead
    ([A-Z]             # Opening capture group and any uppercase letter (to match R & D)
        {              # Opening brace
            (?:        # Opening non-capture group
                [^{}]  # Matches non braces
            |          # OR
                (?1)   # Recurse first capture group
            )+         # Close non-capture group and repeat as many times as necessary
        }              # Closing brace
    )                  # Close of capture group
)                      # Close of positive lookahead