System.Text.RegularExpressions.Regex.Replace Method

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

Syntax

public static string Replace (string input, string pattern, MatchEvaluator evaluator, RegexOptions options)

Parameters

input
The string to search for a match.
pattern
The regular expression pattern to match.
evaluator
A custom method that examines each match and returns either the original matched string or a replacement string.
options
A bitwise combination of the enumeration values that provide options for matching.

Returns

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.

Remarks

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 System.Text.RegularExpressions.Match object in the returned System.Text.RegularExpressions.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 Elements.

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 System.Text.RegularExpressions.MatchEvaluator delegate.

code reference: System.Text.RegularExpressions.Regex.Replace#1

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

If you specify RegexOptions.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 System.Text.RegularExpressions.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(object, object) method to determine whether the method has made any replacements to the input string.

Requirements

Namespace: System.Text.RegularExpressions
Assembly: System (in System.dll)
Assembly Versions: 1.0.5000.0, 2.0.0.0, 4.0.0.0