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Regex.Replace Method (String, String, String, RegexOptions)

In a specified input string, replaces all strings that match a specified regular expression with a specified replacement string. Specified options modify the matching operation.

Namespace:  System.Text.RegularExpressions
Assembly:  System (in System.dll)

'Declaration
Public Shared Function Replace ( _
	input As String, _
	pattern As String, _
	replacement As String, _
	options As RegexOptions _
) As String

Parameters

input
Type: System.String

The string to search for a match.

pattern
Type: System.String

The regular expression pattern to match.

replacement
Type: System.String

The replacement string.

options
Type: System.Text.RegularExpressions.RegexOptions

A bitwise combination of the enumeration values that provide options for matching.

Return Value

Type: System.String
A new string that is identical to the input string, except that the replacement string takes the place of each matched string. If pattern is not matched in the current instance, the method returns the current instance unchanged.

ExceptionCondition
ArgumentException

A regular expression parsing error occurred.

ArgumentNullException

input, pattern, or replacement is Nothing.

ArgumentOutOfRangeException

options is not a valid bitwise combination of RegexOptions values.

RegexMatchTimeoutException

A time-out occurred. For more information about time-outs, see the Remarks section.

The static Replace methods are equivalent to constructing a Regex object with the specified regular expression pattern and calling the instance method Replace.

The pattern parameter consists of regular expression language elements that symbolically describe the string to match. For more information about regular expressions, see .NET Framework Regular Expressions and Regular Expression Language - Quick Reference. If you specify RightToLeft for the options parameter, the search for matches begins at the end of the input string and moves left; otherwise, the search begins at the start of the input string and moves right.

The replacement parameter specifies the string that is to replace each match in input. replacement can consist of any combination of literal text and substitutions. For example, the replacement pattern a*${test}b inserts the string "a*" followed by the substring that is matched by the test capturing group, if any, followed by the string "b". The * character is not recognized as a metacharacter within a replacement pattern.

NoteNote

Substitutions are the only regular expression language elements that are recognized in a replacement pattern. All other regular expression language elements, including character escapes, are allowed in regular expression patterns only and are not recognized in replacement patterns.

The RegexMatchTimeoutException exception is thrown if the execution time of the replacement operation exceeds the time-out interval specified for the application domain in which the method is called. If no time-out is defined in the application domain's properties, or if the time-out value is Regex.InfiniteMatchTimeout, no exception is thrown.

Because the method returns input unchanged if there is no match, you can use the Object.ReferenceEquals method to determine whether the method has made any replacements to the input string.

Notes to Callers

This method times out after an interval that is equal to the default time-out value of the application domain in which it is called. If a time-out value has not been defined for the application domain, the value Regex.InfiniteMatchTimeout, which prevents the method from timing out, is used. The recommended static method for replacing a pattern match is Regex.Replace(String, String, String, RegexOptions, TimeSpan), which lets you set the time-out interval.

The following example uses the Replace(String, String, String, RegexOptions) method to replace the local machine and drive names in a UNC path with a local file path. The regular expression uses the Environment.MachineName property to include the name of the local computer, and the Environment.GetLogicalDrives method to include the names of the logical drives. All regular expression string comparisons are case-insensitive. To run the example successfully, you should replace the literal string "MyMachine" with your local machine name.

Imports System.Text.RegularExpressions

Module Example
   Public Sub Main()
      ' Get drives available on local computer and form into a single character expression. 
      Dim drives() As String = Environment.GetLogicalDrives()
      Dim driveNames As String = Nothing 
      For Each drive As String In drives
         driveNames += drive.Substring(0,1)
      Next 
      ' Create regular expression pattern dynamically based on local machine information. 
      Dim pattern As String = "\\\\" + Environment.MachineName + "(?:\.\w+)*\\([" + driveNames + "])\$" 

      Dim replacement As String = "$1:" 
      Dim uncPaths() AS String = {"\\MyMachine.domain1.mycompany.com\C$\ThingsToDo.txt", _
                                  "\\MyMachine\c$\ThingsToDo.txt", _
                                  "\\MyMachine\d$\documents\mydocument.docx" } 

      For Each uncPath As String In uncPaths
         Console.WriteLine("Input string: " + uncPath)
         Console.WriteLine("Returned string: " + Regex.Replace(uncPath, pattern, replacement, RegexOptions.IgnoreCase))
         Console.WriteLine()
      Next 
   End Sub 
End Module 
' The example displays the following output if run on a machine whose name is 
' MyMachine: 
'    Input string: \\MyMachine.domain1.mycompany.com\C$\ThingsToTo.txt 
'    Returned string: C:\ThingsToDo.txt 
'     
'    Input string: \\MyMachine\c$\ThingsToDo.txt 
'    Returned string: c:\ThingsToDo.txt 
'     
'    Input string: \\MyMachine\d$\documents\mydocument.docx 
'    Returned string: d:\documents\mydocument.docx

The regular expression pattern is defined by the following expression:

"\\\\" + Environment.MachineName + "(?:\.\w+)*\\([" + driveNames + "])\$"

The following table shows how the regular expression pattern is interpreted.

Pattern

Description

\\\\

Match two consecutive backslash (\) characters. Because the backslash character is interpreted as the escape character, each backslash must be escaped with another backslash.

+ Environment.MachineName +

Match the string that is returned by the Environment.MachineName property.

(?:\.\w+)*

Match the period (.) character followed by one or more word characters. This match can occur zero or more times. The matched subexpression is not captured.

\\

Match a backslash (\) character.

([" + driveNames + "])

Match the character class that consists of the individual drive letters. This match is the first captured subexpression.

\$

Match the literal dollar sign ($) character.

The replacement pattern $1 replaces the entire match with the first captured subexpression. That is, it replaces the UNC machine and drive name with the drive letter.

.NET Framework

Supported in: 4.5.2, 4.5.1, 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

.NET for Windows Store apps

Supported in: Windows 8

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone 8, Silverlight 8.1

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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