RegEx匹配模式,只要它没有前面的不同模式

Question

我需要一个用于文本替换的正则表达式.示例:要匹配的文本ABC(可以用方括号括起来),替换文本是DEF.这很基本.该复杂的是,我不希望在比赛ABC时,它是由前面的图案文字\[[\d ]+\]\.-换句话说,当一个单词之前或设置在括号中的词,随后一段时间.

以下是要匹配的源文本的一些示例,以及在进行正则表达式替换后的结果:

1. [xxx xxx].[ABC] > [xxx xxx].[ABC] (does not match - first part fits the pattern)
2. [xxx xxx].ABC   > [xxx xxx].ABC   (does not match - first part fits the pattern)
3. [xxx.ABC        > [xxx.DEF        (matches - first part has no closing bracket)
4. [ABC]           > [DEF]           (matches - no first part)
5. ABC             > DEF             (matches - no first part)
6. [xxx][ABC]      > [xxx][DEF]      (matches - no period in between)
7. [xxx]. [ABC]    > [xxx] [DEF]     (matches - space in between)

它归结为:我如何指定前面的模式,如上所述,将阻止匹配？在这种情况下,模式会是什么？(正则表达式的C#风味)

Answer 1

你想要一个负面的后视表达.这些看起来像(?<!pattern),所以:

(?<!\[[\d ]+\]\.)\[?ABC\]?

请注意,这不会强制ABC周围的一对匹配的方括号; 它只允许一个可选的开放式支架和一个可选的紧密支架.如果你想强制匹配一对或没有,你必须使用交替:

(?<!\[[\d ]+\]\.)(?:ABC|\[ABC\])

这使用非捕获括号来分隔交替.如果您想要实际捕获ABC,可以将其转换为捕获组.

ETA:第一个表达式似乎失败的原因是它匹配on ABC],而不是禁止文本.开放式支架[是可选的,因此它与之不匹配.解决这个问题的方法是将可选的开放式支架[转换为负面的后置断言,如下所示:

(?<!\[[\d ]+\]\.\[?)ABC\]?

它匹配和不匹配的一个例子:

[123].[ABC]: fail (expected: fail)
[123 456].[ABC]: fail (expected: fail)
[123.ABC: match (expected: match)
    matched: ABC
ABC: match (expected: match)
    matched: ABC
[ABC]: match (expected: match)
    matched: ABC]
[ABC[: match (expected: fail)
    matched: ABC

试图使一个开放式支架的存在[迫使一个匹配的紧密支架],如第二个模式所预期的那样,比较棘手,但这似乎有效:

(?:(?<!\[[\d ]+\]\.\[)ABC\]|(?<!\[[\d ]+\]\.)(?<!\[)ABC(?!\]))

它匹配和不匹配的一个例子:

[123].[ABC]: fail (expected: fail)
[123 456].[ABC]: fail (expected: fail)
[123.ABC: match (expected: match)
    matched: ABC
ABC: match (expected: match)
    matched: ABC
[ABC]: match (expected: match)
    matched: ABC]
[ABC[: fail (expected: fail)

这些示例是使用以下代码生成的:

// Compile and run with: mcs so_regex.cs && mono so_regex.exe
using System;
using System.Text.RegularExpressions;

public class SORegex {
  public static void Main() {
    string[] values = {"[123].[ABC]", "[123 456].[ABC]", "[123.ABC", "ABC", "[ABC]", "[ABC["};
    string[] expected = {"fail", "fail", "match", "match", "match", "fail"};
    string pattern = @"(?<!\[[\d ]+\]\.\[?)ABC\]?";  // Don't force [ to match ].
    //string pattern = @"(?:(?<!\[[\d ]+\]\.\[)ABC\]|(?<!\[[\d ]+\]\.)(?<!\[)ABC(?!\]))";  // Force balanced brackets.
    Console.WriteLine("pattern: {0}", pattern);
    int i = 0;
    foreach (string text in values) {
      Match m = Regex.Match(text, pattern);
      bool isMatch = m.Success;
      Console.WriteLine("{0}: {1} (expected: {2})", text, isMatch? "match" : "fail", expected[i++]);
      if (isMatch) Console.WriteLine("\tmatched: {0}", m.Value);
    }
  }
}