c# - .Net Core 正则表达式、命名组、嵌套组、反向引用和惰性限定符

Question

我正在尝试使用 .Net Core 2.1 从看起来像标记的字符串中解析键值对。

考虑下面的示例 Program.cs 文件...

我的问题是:

1.

我怎样才能写出模式 kvp充当“键和值(如果存在)”而不是当前行为的“键或值”？

例如，在测试用例2的输出中，而不是:

=============================
input = <tag KEY1="vAl1">

--------------------
kvp[0] = KEY1
          key   =       KEY1
        value   =
--------------------
kvp[1] = vAl1
          key   =
        value   =       vAl1
=============================

我想看看:

=============================
input = <tag KEY1="vAl1">

--------------------
kvp[0] = KEY1="vAl1"
          key   =       KEY1
        value   =       vAl1
=============================

不破坏测试用例 9:

=============================
input = <tag noValue1 noValue2>

--------------------
kvp[0] = noValue1
          key   =       noValue1
        value   =
--------------------
kvp[1] = noValue2
          key   =       noValue2
        value   =
=============================

2.

我怎样才能写出模式 value在名为“quotes”的组匹配的下一个字符处停止匹配？换句话说，下一个平衡报价。我显然误解了反向引用的工作原理，我的理解是 \k<quotes>将替换为运行时匹配的值(不是设计时定义的模式)由 (?<quotes>[""'`]) .

例如，在测试用例5的输出中，而不是:

--------------------
kvp[4] =  key3='hello,
          key   =
        value   =        key3='hello,
--------------------
kvp[5] = experts
          key   =
        value   =       experts
=============================

我想看看(尽管有问题 1 的解决方案):

--------------------
kvp[4] =  key3
          key   =        key3
        value   =
--------------------
kvp[5] = hello, "experts"
          key   =
        value   =       hello, "experts"
=============================

3.

我怎样才能写出模式 value在 /> 之前停止匹配？在测试用例 7 中，key2 的值应该是 thing-1 .我不记得我尝试过的所有内容，但我还没有找到一种在不破坏测试用例 6 的情况下工作的模式，其中 / 是值的一部分。

---

程序.cs

using System;
using System.Reflection;
using System.Text.RegularExpressions;

namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            RegExTest();

            Console.ReadLine();
        }

        static void RegExTest()
        {
            // Test Cases
            var case1 = @"<tag>";
            var case2 = @"<tag KEY1=""vAl1"">";
            var case3 = @"<tag kEy2='val2'>";
            var case4 = @"<tag key3=`VAL3`>";
            var case5 = @"<tag           key1='val1' 

                        key2=""http://www.w3.org"" key3='hello, ""experts""'>";
            var case6 = @"<tag :key1 =some/thing>";
            var case7 = @"<tag key2=thing-1/>";
            var case8 = @"<tag key3      =        thing-2>";
            var case9 = @"<tag noValue1 noValue2>";
            var case10 = @"<tag/>";
            var case11 = @"<tag />";

            // A key may begin with a letter, underscore or colon, follow by 
            // zero or more of those, or numbers, periods, or dashs.
            string key = @"(?<key>(?<=\s+)[a-z_:][a-z0-9_:\.-]*?(?=[\s=>]+))";

            // A value may contain any character, and must be wrapped in balanced quotes (double, single, 
            // or back) if the value contains any quote, whitespace, equal, or greater- or less- than 
            // character.
            string value = @"(?<value>((?<=(?<quotes>[""'`])).*?(?=\k<quotes>)|(?<=[=][\s]*)[^""'`\s=<>]+))";

            // A key-value pair must contain a key, 
            // a value is optional
            string kvp = $"(?<kvp>{key}|{value})"; // Without the | (pipe), it doesn't match any test case...

            // ...value needs to be optional (case9), tried:
            //kvp = $"(?<kvp>{key}{value}?)";
            //kvp = $"(?<kvp>{key}({value}?))";
            //kvp = $"(?<kvp>{key}({value})?)";
            // ...each only matches key, but also matches value in case8 as key

            Regex getKvps = new Regex(kvp, RegexOptions.IgnoreCase);

            FormatMatches(getKvps.Matches(case1)); // OK

            FormatMatches(getKvps.Matches(case2)); // OK

            FormatMatches(getKvps.Matches(case3)); // OK

            FormatMatches(getKvps.Matches(case4)); // OK

            FormatMatches(getKvps.Matches(case5)); // Backreference and/or lazy qualifier doesn't work.

            FormatMatches(getKvps.Matches(case6)); // OK

            FormatMatches(getKvps.Matches(case7)); // The / is not part of the value.

            FormatMatches(getKvps.Matches(case8)); // OK

            FormatMatches(getKvps.Matches(case9)); // OK

            FormatMatches(getKvps.Matches(case10)); // OK

            FormatMatches(getKvps.Matches(case11)); // OK
        }

        static void FormatMatches(MatchCollection matches)
        {
            Console.WriteLine(new string('=', 78));

            var _input = matches.GetType().GetField("_input",
                BindingFlags.NonPublic |
                BindingFlags.Instance)
                .GetValue(matches);

            Console.WriteLine($"input = {_input}");
            Console.WriteLine();

            if (matches.Count < 1)
            {
                Console.WriteLine("[kvp not matched]");
                return;
            }

            for (int i = 0; i < matches.Count; i++)
            {
                Console.WriteLine(new string('-', 20));

                Console.WriteLine($"kvp[{i}] = {matches[i].Groups["kvp"]}");
                Console.WriteLine($"\t  key\t=\t{matches[i].Groups["key"]}");
                Console.WriteLine($"\tvalue\t=\t{matches[i].Groups["value"]}");
            }
        }
    }
}

Answer 1

你可以使用

\s(?<key>[a-z_:][a-z0-9_:.-]*)(?:\s*=\s*(?:(?<q>[`'"])(?<value>.*?)\k<q>|(?<value>(?:(?!/>)[^\s`'"<>])+)))?

参见 regex demo突出显示组和 .NET regex demo (证明)。

C# 用法:

var pattern = @"\s(?<key>[a-z_:][a-z0-9_:.-]*)(?:\s*=\s*(?:(?<q>[`'""])(?<value>.*?)\k<q>|(?<value>(?:(?!/>)[^\s`'""<>])+)))?";
var matches = Regex.Matches(case, pattern, RegexOptions.IgnoreCase);
foreach (Match m in matches)
{
    Console.WriteLine(m.Value);                 // The whole match
    Console.WriteLine(m.Groups["key"].Value);   // Group "key" value
    Console.WriteLine(m.Groups["value"].Value); // Group "value" value
}

详情

• \s - 一个空格
• (?<key>[a-z_:][a-z0-9_:.-]*) - 组“键”:一封信，_或 :然后是 0+ 个字母、数字、_ , : , .或 -
• (?:\s*=\s*(?:(?[<code>'"])(?<value>.*?)\k<q>|(?<value>(?:(?!/>)[^\s</code>'"<>])+)))? - 一次或零次出现(因此该值是可选的):
  • \s*=\s* - 一个 =用 0+ 个空格括起来
  • (?: - 非捕获组的开始:
    • (?[`'"]) - 分隔符，` , '或 "
    • (?<value>.*?) - 将匹配除换行字符以外的任何 0+ 个字符的“值”分组尽可能少
    • \k<q> - 对组“q”的反向引用，相同的值必须匹配
  • | - 或者
    • <code>(?<value></code>(?:(?!/>)[^\s`'"<>])+) - 组“值”:空格以外的字符，` , ' , " , <和 > ，出现 1 次或多次，不会启动 />字符序列
• ) - 非捕获组结束。