正则表达式是可以与输入文本进行匹配的模式。.Net 框架提供了允许这种匹配的正则表达式引擎。模式由一个或多个字符文字，运算符或构造组成。

用于定义正则表达式的构造

有各种类型的字符，运算符和结构可以让你定义正则表达式。 点击下面的链接来查看这些结构。

• 字符转义
• Character类
• 锚定
• 分组结构
• 量词
• 反向引用结构
• 交替结构
• 替换结构
• 杂项结构

Regex类

Regex类用于表示正则表达式，Regex类有以下常用的方法：

有关方法和属性的完整列表，请参阅Microsoft文档。

1. 示例1

以下示例匹配以S开头的单词：

Imports System.Text.RegularExpressions
Module regexProg
   Sub showMatch(ByVal text As String, ByVal expr As String)
      Console.WriteLine("The Expression: " + expr)
      Dim mc As MatchCollection = Regex.Matches(text, expr)
      Dim m As Match
      For Each m In mc
          Console.WriteLine(m)
      Next m
   End Sub
   Sub Main()
      Dim str As String = "A Thousand Splendid Suns"
      Console.WriteLine("Matching words that start with 'S': ")
      showMatch(str, "\bS\S*")
      Console.ReadKey()
   End Sub
End Module

执行上面示例代码，得到以下结果 -

Matching words that start with 'S':
The Expression: \bS\S*
Splendid
Suns

2. 示例2

以下示例匹配以m开始并以e结尾的单词：

Imports System.Text.RegularExpressions
Module regexProg
   Sub showMatch(ByVal text As String, ByVal expr As String)
      Console.WriteLine("The Expression: " + expr)
      Dim mc As MatchCollection = Regex.Matches(text, expr)
      Dim m As Match
      For Each m In mc
          Console.WriteLine(m)
      Next m
   End Sub
   Sub Main()
      Dim str As String = "make a maze and manage to measure it"
      Console.WriteLine("Matching words that start with 'm' and ends with 'e': ")
      showMatch(str, "\bm\S*e\b")
      Console.ReadKey()
   End Sub
End Module

执行上面示例代码，得到以下结果 -

Matching words start with 'm' and ends with 'e':
The Expression: \bm\S*e\b
make
maze
manage
measure

3. 示例3

这个例子替换额外(多余)的空格符：

Imports System.Text.RegularExpressions
Module regexProg
   Sub Main()
      Dim input As String = "Hello    World   "
      Dim pattern As String = "\\s+"
      Dim replacement As String = " "
      Dim rgx As Regex = New Regex(pattern)
      Dim result As String = rgx.Replace(input, replacement)
      Console.WriteLine("Original String: {0}", input)
      Console.WriteLine("Replacement String: {0}", result)
      Console.ReadKey()
   End Sub
End Module

执行上面示例代码，得到以下结果 -

Original String: Hello   World   
Replacement String: Hello World