.Net 正则表达式用捕获组替换重复出现的模式

Question

我有一个类似这样的 SQL 脚本：

DECLARE @MyVariable1 = 1
DECLARE @MyVariable1 = 10
DECLARE @MyVariable3 = 15
DECLARE @MyVariable2 = 20
DECLARE @MyVariable1 = 7
DECLARE @MyVariable2 = 4
DECLARE @MyVariable4 = 7
DECLARE @MyVariable2 = 4

当然，真正的脚本中间还有很多其他的东西，但我想写一个给定上述输入的函数，输出如下：

DECLARE @MyVariable1 = 1
@MyVariable1 = 10
DECLARE @MyVariable3 = 15
DECLARE @MyVariable2 = 20
@MyVariable1 = 7
@MyVariable2 = 4
DECLARE @MyVariable4 = 7
@MyVariable2 = 4

基本上删除了已声明变量的重复 DECLARE 语句

我目前的解决方案是这样的：

    Private Function RemoveDuplicateDeclarations(commandText As String) As String
        Dim lines = commandText.Split(New String() { vbCrLf }, StringSplitOptions.RemoveEmptyEntries)
        Dim declarationRegex As New Regex("(\r|\n|\r\n) *DECLARE *(?<initialization>(?<varname>[^ ]*) *.*)" & vbCrLf , RegexOptions.Multiline Or RegexOptions.IgnoreCase)
        Dim declaredVariables As New List(Of String) 
        Dim resultBuilder As New StringBuilder()

        For Each line In lines    
            Dim matches = declarationRegex.Matches(line)
            If matches.Count > 0 Then
                Dim varname = matches(0).Groups("varname").Value
                If declaredVariables.Contains(varname) Then
                    resultBuilder.AppendLine(declarationRegex.Replace(line, "${initialization}"))
                Else 
                    declaredVariables.Add(varname)

                    resultBuilder.AppendLine(line)
                End If
            Else
                resultBuilder.AppendLine(line)
            End If
        Next

        Return resultBuilder.ToString()
    End Function

它非常适合我的脚本（并且不会有任何新脚本），但它似乎有点过于复杂，因为我可以匹配我想要替换的内容我想知道是否有办法只需使用一些参数运行Regex.Replace() 并在一行中完成它

欢迎使用 C# 解决方案

-编辑-

为了澄清我想要实现的目标，我想要以下格式的答案，或者解释这是不可能的（允许修改正则表达式）。

Private Function RemoveDuplicateDeclarations(commandText As String) As String
    Dim regex As New Regex("(\r|\n|\r\n) *DECLARE *(?<initialization>(?<varname>[^ ]*) *.*)" & vbCrLf , RegexOptions.Multiline Or RegexOptions.IgnoreCase)
    Return regex.Replace(commandText, "What do I put here???????")
End Function

Answer 1

您可以使用一个相当简单的正则表达式来搜索行中重复的 @ 前缀词，并且只将第一次出现在循环中，直到没有匹配。

(?sm)(^DECLARE\s+(@\w+\b).*?)^DECLARE\s+\2

详情：

• (?sm) - 启用 MULTILINE 和 Singleline (DOTALL) 模式
• (^DECLARE\s+(@\w+\b).*?) - 第 1 组捕获：
  • ^DECLARE - DECLARE 在行首
  • \s+ - 1 个或多个空格符号
  • (@\w+\b) - 第 2 组捕获 @ 和 1+ 个单词字符，直到尾随单词边界
  • .*? - 任何 0+ 个字符，尽可能少，直到第一次出现...
• ^DECLARE - 一行开头的 DECLARE 子字符串
• \s+ - 1+ 个空格
• \2 - 对存储在第 2 组中的值的反向引用

见VB.NET demo：

Dim rx As Regex = New Regex("(?sm)(^DECLARE\s+(@\w+\b).*?)^DECLARE\s+\2")
Dim s As String = "DECLARE @MyVariable1 = 1" & vbCrLf & "DECLARE @MyVariable1 = 10" & vbCrLf & "DECLARE @MyVariable3 = 15" & vbCrLf & "DECLARE @MyVariable2 = 20" & vbCrLf & "DECLARE @MyVariable1 = 7" & vbCrLf & "DECLARE @MyVariable2 = 4" & vbCrLf & "DECLARE @MyVariable4 = 7" & vbCrLf & "DECLARE @MyVariable2 = 4"
Dim res As String
Dim tmp As String = s
res = rx.Replace(s, "$1$2")
While (String.Compare(tmp, res) <> 0)
    tmp = res
    res = rx.Replace(res, "$1$2")
End While
Console.WriteLine(res)

输出：

DECLARE @MyVariable1 = 1
@MyVariable1 = 10
DECLARE @MyVariable3 = 15
DECLARE @MyVariable2 = 20
@MyVariable1 = 7
@MyVariable2 = 4
DECLARE @MyVariable4 = 7
@MyVariable2 = 4

Answer 2

如果您喜欢 linq 解决方案：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;
using System.IO;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            string input =
                "DECLARE @MyVariable1 = 1\n" +
                "DECLARE @MyVariable1 = 10\n" +
                "DECLARE @MyVariable3 = 15\n" +
                "DECLARE @MyVariable2 = 20\n" +
                "DECLARE @MyVariable1 = 7\n" +
                "DECLARE @MyVariable2 = 4\n" +
                "DECLARE @MyVariable4 = 7\n" +
                "DECLARE @MyVariable2 = 4\n";

            string pattern = @"@(?'name'[^\s]+)\s+=\s+(?'value'\d+)";

            MatchCollection matches = Regex.Matches(input, pattern);

            string[] lines = matches.Cast<Match>()
                .Select((x, i) => new { name = x.Groups["name"].Value, value = x.Groups["value"].Value, index = i })
                .GroupBy(x => x.name)
                .Select(x => x.Select((y, i) =>  new { 
                    index = y.index,  
                    s = i == 0 
                       ? string.Format("DECLARE @{0} = {1}", x.Key, y.value)  
                       : string.Format("@{0} = {1}", x.Key, y.value) 
                }))
                .SelectMany(x => x)
                .OrderBy(x => x.index)
                .Select(x => x.s)
                .ToArray();

            foreach (string line in lines)
            {
                Console.WriteLine(line);
            }
            Console.ReadLine();

        }
    }
}