• Article

Regex.Replace Method (String, String)

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Within a specified input string, replaces all strings that match a regular expression pattern with a specified replacement string.

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

Syntax

'Declaration
Public Function Replace ( _
    input As String, _
    replacement As String _
) As String

public string Replace(
    string input,
    string replacement
)

Parameters

Return Value

Type: System.String
A new string that is identical to the input string, except that a replacement string takes the place of each matched string.

Exceptions

Exception Condition
ArgumentNullException

input is nulla null reference (Nothing in Visual Basic).

-or-

replacement is nulla null reference (Nothing in Visual Basic).

Remarks

The search for matches starts at the beginning of the input parameter string. The regular expression is the pattern defined by the constructor for the current Regex object.

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.

Examples

The following example defines a regular expression, \s+, that matches one or more white-space characters. The replacement string, " ", replaces them with a single space character.

Imports System.Text.RegularExpressions

Module Example
   Public Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)
      Dim input As String = "This is   text with   far  too   much   " + _
                            "whitespace."
      Dim pattern As String = "\s+"
      Dim replacement As String = " "
      Dim rgx As New Regex(pattern)
      Dim result As String = rgx.Replace(input, replacement)

      outputBlock.Text += String.Format("Original String: {0}", input) & vbCrLf
      outputBlock.Text += String.Format("Replacement String: {0}", result) & vbCrLf
   End Sub
End Module
' The example displays the following output:
'          Original String: This is   text with   far  too   much   whitespace.
'          Replacement String: This is text with far too much whitespace.

using System;
using System.Text.RegularExpressions;

public class Example
{
   public static void Demo(System.Windows.Controls.TextBlock outputBlock)
   {
      string input = "This is   text with   far  too   much   " +
                     "whitespace.";
      string pattern = "\\s+";
      string replacement = " ";
      Regex rgx = new Regex(pattern);
      string result = rgx.Replace(input, replacement);

      outputBlock.Text += String.Format("Original String: {0}", input) + "\n";
      outputBlock.Text += String.Format("Replacement String: {0}", result) + "\n";
   }
}
// The example displays the following output:
//       Original String: This is   text with   far  too   much   whitespace.
//       Replacement String: This is text with far too much whitespace.

The following example defines a regular expression, (\p{Sc}\s?)?(\d+\.?((?<=\.)\d+)?)(?(1)|\s?\p{Sc})?, that removes either a leading or a trailing currency symbol from a numeric value.

Imports System.Text.RegularExpressions

Module Example
   Public Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)
      Dim pattern As String = "(\p{Sc}\s?)?(\d+\.?((?<=\.)\d+)?)(?(1)|\s?\p{Sc})?"
      Dim input As String = "$17.43  €2 16.33  £0.98  0.43   £43   12€  17"
      Dim replacement As String = "$2"
      Dim rgx As New Regex(pattern)
      Dim result As String = rgx.Replace(input, replacement)

      outputBlock.Text += String.Format("Original String:    '{0}'", input) & vbCrLf
      outputBlock.Text += String.Format("Replacement String: '{0}'", result) & vbCrLf
   End Sub
End Module
' The example displays the following output:
'       Original String:    '$17.43  €2 16.33  £0.98  0.43   £43   12€  17'
'       Replacement String: '17.43  2 16.33  0.98  0.43   43   12  17'

using System;
using System.Text.RegularExpressions;

public class Example
{
   public static void Demo(System.Windows.Controls.TextBlock outputBlock)
   {
      string pattern = @"(\p{Sc}\s?)?(\d+\.?((?<=\.)\d+)?)(?(1)|\s?\p{Sc})?";
      string input = "$17.43  €2 16.33  £0.98  0.43   £43   12€  17";
      string replacement = "$2";
      Regex rgx = new Regex(pattern);
      string result = rgx.Replace(input, replacement);

      outputBlock.Text += String.Format("Original String:    '{0}'", input) + "\n";
      outputBlock.Text += String.Format("Replacement String: '{0}'", result) + "\n";
   }
}
// The example displays the following output:
//       Original String:    '$17.43  €2 16.33  £0.98  0.43   £43   12€  17'
//       Replacement String: '17.43  2 16.33  0.98  0.43   43   12  17'

The regular expression is interpreted as shown in the following table.

Pattern

Description

\p{Sc}

Match a currency symbol.

\s?

Match zero or one white-space character.

(\p{Sc}\s?)?

Match zero or one occurrence of the combination of a currency symbol followed by zero or one white-space character. This is the first capturing group.

\d+

Match one or more decimal digits.

\.?

Match zero or one occurrence of a period (used as a decimal separator character).

((?<=\.)\d+)?

If a period is the previous character, match one or more decimal digits. This pattern can be matched either zero or one time.

(\d+\.?((?<=\.)\d+)?)

Match the pattern of one or more decimal digits followed by an optional period and additional decimal digits. This is the second capturing group.

(?(1)|\s?\p{Sc})?

If the first captured group exists, match an empty string. Otherwise, match zero or one white-space character followed by a currency symbol.

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.