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Regex.Replace Method (String, String)

Updated: December 2009

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)

public string Replace(
	string input,
	string replacement
)

Parameters

input
Type: System.String

The string to search for a match.

replacement
Type: System.String

The replacement string.

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.

ExceptionCondition
ArgumentNullException

input is null.

-or-

replacement is null.

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.

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.

using System;
using System.Text.RegularExpressions;

public class Example
{
   public static void Main()
   {
      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);

      Console.WriteLine("Original String: {0}", input);
      Console.WriteLine("Replacement String: {0}", result);                             
   }
}
// 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.

using System;
using System.Text.RegularExpressions;

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

      Console.WriteLine("Original String:    '{0}'", input);
      Console.WriteLine("Replacement String: '{0}'", result);                             
   }
}
// The example displays the following output: 
//    Original String:    '$17.43  â‚2 16.33  £0.98  0.43   £43   12â‚   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.

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune

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

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 3.5, 2.0, 1.0

XNA Framework

Supported in: 3.0, 2.0, 1.0

Date

History

Reason

December 2009

Expanded the Remarks section and replaced the example.

Customer feedback.

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