Post By: Hanan Mannan
Contact Number: Pak (+92)-321-59-95-634
-------------------------------------------------------

VB.Net - Regular Expressions

A regular expression is a pattern that could be matched against an input text. The .Net framework provides a regular expression engine that allows such matching. A pattern consists of one or more character literals, operators, or constructs.

The Regex Class

The Regex class is used for representing a regular expression.

The Regex class has the following commonly used methods:

S.N	Methods & Description
1	Public Function IsMatch ( input As String ) As Boolean  Indicates whether the regular expression specified in the Regex constructor finds a match in a specified input string.
2	Public Function IsMatch ( input As String, startat As Integer ) As Boolean  Indicates whether the regular expression specified in the Regex constructor finds a match in the specified input string, beginning at the specified starting position in the string.
3	Public Shared Function IsMatch ( input As String, pattern As String ) As Boolean  Indicates whether the specified regular expression finds a match in the specified input string.
4	Public Function Matches ( input As String ) As MatchCollection  Searches the specified input string for all occurrences of a regular expression.
5	Public Function Replace ( input As String, replacement As String ) As String  In a specified input string, replaces all strings that match a regular expression pattern with a specified replacement string.
6	Public Function Split ( input As String ) As String()  Splits an input string into an array of substrings at the positions defined by a regular expression pattern specified in the Regex constructor.

For the complete list of methods and properties, please consult Microsoft documentation.

Example 1

The following example matches words that start with 'S':

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

When the above code is compiled and executed, it produces the following result:

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

Example 2

The following example matches words that start with 'm' and ends with 'e':

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

When the above code is compiled and executed, it produces the following result:

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

Example 3

This example replaces extra white space:

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

When the above code is compiled and executed, it produces the following result:

Original String: Hello   World   
Replacement String: Hello World