高级替换
一些编程语言有自己的正则表达式特性，例如，$+术语（在 C#，Perl，VB 等中）将匹配的文本替换为捕获的最后一个组。
例：
using System;
using System.Text.RegularExpressions;
public class Example
{
public static void Main()
{
string pattern = @"\b(\w+)\s\1\b";
string substitution = "$+";
string input = "The the dog jumped over the fence fence.";
Console.WriteLine(Regex.Replace(input, pattern, substitution,
RegexOptions.IgnoreCase));
}
}
// The example displays the following output:
// The dog jumped over the fence.
Microsoft 官方开发者网络示例 [1]
其他罕见的替代术语是$` 和 $'：
$` =替换匹配字符串前的文本匹配
$' = 将匹配字符串替换为匹配字符串后的文本
由于这个事实，这些替换字符串应该像这样工作：
Regex: /part2/
Input: "part1part2part3"
Replacement: "$`"
Output: "part1part1part3" //Note that part2 was replaced with part1, due &` termRegex: /part2/
Input: "part1part2part3"
Replacement: "$'"
Output: "part1part3part3" //Note that part2 was replaced with part3, due &' term
以下是在一段 javascript 上进行这些替换的示例：
var rgx = /middle/;
var text = "Your story must have a beginning, middle, and end"
console.log(text.replace(rgx, "$`"));
//Logs: "Your story must have a beginning, Your story must have a beginning, , and end"
console.log(text.replace(rgx, "$'"))
//Logs: "Your story must have a beginning, , and end, and end"
还有术语 $_，它可以检索整个匹配的文本：
Regex: /part2/
Input: "part1part2part3"
Replacement: "$_"
Output: "part1part1part2part3part3" //Note that part2 was replaced with part1part2part3,
// due $_ term
将其转换为 VB 将为我们提供：
Imports System.Text.RegularExpressions
Module Example
Public Sub Main()
Dim input As String = "ABC123DEF456"
Dim pattern As String = "\d+"
Dim substitution As String = "$_"
Console.WriteLine("Original string: {0}", input)
Console.WriteLine("String with substitution: {0}", _
Regex.Replace(input, pattern, substitution))
End Sub
End Module
' The example displays the following output:
' Original string: ABC123DEF456
' String with substitution: ABCABC123DEF456DEFABC123DEF456
Microsoft 官方开发者网络示例 [2]
并且最后但并非最不重要的替换术语是 $$，其转换为正则表达式将与\$（文字 $ 的转义版本 ）相同。
如果你想匹配一个像这样的字符串：例如 USD: $3.99，并想要存储 3.99，但只用一个正则表达式替换为 $3.99，你可以使用：
Regex: /USD:\s+\$([\d.]+)/
Input: "USD: $3.99"
Replacement: "$$$1"
To Store: "$1"
Output: "$3.99"
Stored: "3.99"
如果你想使用 Javascript 进行测试，可以使用以下代码：
var rgx = /USD:\s+\$([\d.]+)/;
var text = "USD: $3.99";
var stored = parseFloat(rgx.exec(text)[1]);
console.log(stored); //Logs 3.99
console.log(text.replace(rgx, "$$$1")); //Logs $3.99