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

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

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

static member Replace : 
        input:string * 
        pattern:string * 
        evaluator:MatchEvaluator * 
        options:RegexOptions -> string

Parameters

input
Type: System.String

The string to search for a match.

pattern
Type: System.String

The regular expression pattern to match.

evaluator
Type: System.Text.RegularExpressions.MatchEvaluator

A custom method that examines each match and returns either the original matched string or a 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 a 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 evaluator is a null reference (Nothing in Visual Basic).

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 Regex.Replace(String, String, MatchEvaluator, RegexOptions) method is useful for replacing a regular expression match in if any of the following conditions is true:

  • The replacement string cannot readily be specified by a regular expression replacement pattern.

  • The replacement string results from some processing done on the matched string.

  • The replacement string results from conditional processing.

The method is equivalent to calling the Regex.Matches(String, String, RegexOptions) method and passing each Match object in the returned MatchCollection collection to the evaluator delegate.

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.

The evaluator parameter is the delegate for a custom method that you define and that examines each match. The custom method must have the following signature to match the MatchEvaluator delegate.

No code example is currently available or this language may not be supported.

Your custom method returns a string that replaces the matched input.

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 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.

The following example uses a regular expression to extract the individual words from a string, and then uses a MatchEvaluator delegate to call a method named WordScramble that scrambles the individual letters in the word. To do this, the WordScramble method creates an array that contains the characters in the match. It also creates a parallel array that it populates with random floating-point numbers. The arrays are sorted by calling the Array.Sort(TKey, TValue)(TKey[], TValue[], IComparer(TKey)) method, and the sorted array is provided as an argument to a String class constructor. This newly created string is then returned by the WordScramble method. The regular expression pattern \w+ matches one or more word characters; the regular expression engine will continue to add characters to the match until it encounters a non-word character, such as a white-space character. The call to the Replace(String, String, MatchEvaluator, RegexOptions) method includes the RegexOptions.IgnorePatternWhitespace option so that the comment in the regular expression pattern \w+ # Matches all the characters in a word. is ignored by the regular expression engine.

No code example is currently available or this language may not be supported.

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0, 1.1

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

XNA Framework

Supported in: 3.0, 2.0, 1.0

Portable Class Library

Supported in: Portable Class Library

Supported in: Windows Phone 8.1

Supported in: Windows Phone Silverlight 8.1

Supported in: Windows Phone Silverlight 8
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