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.
Constructs for Defining Regular Expressions
There are various categories of characters, operators, and constructs that lets you to define regular expressions. Click the follwoing links to find these constructs.- Character escapes
- Character classes
- Anchors
- Grouping constructs
- Quantifiers
- Backreference constructs
- Alternation constructs
- Substitutions
- Miscellaneous 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. |
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 ModuleWhen 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 ModuleWhen 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 ModuleWhen the above code is compiled and executed, it produces the following result:
Original String: Hello World Replacement String: Hello World
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