\1 match the value of the first capture.

   

Imports System.Text.RegularExpressions

Module Example
   Public Sub Main()
      Dim pattern As String = "(\w)\1"
      Dim words() As String = { "this", "is", "a", "test"}
      For Each word As String In words
         Dim match As Match = Regex.Match(word, pattern)
         If match.Success Then
            Console.WriteLine("'{0}' found in '{1}' at position {2}.",match.Value, word, match.Index)
         Else
            Console.WriteLine("No double characters in '{0}'.", word)
         End If
      Next                                                  
   End Sub
End Module

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\1 match the value of the first capture. : Regular Expressions « Development « VB.Net

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