System.Text.RegularExpressions.Regex.Replace Method

In a specified input string, replaces all substrings that match a specified regular expression with a string returned by a System.Text.RegularExpressions.MatchEvaluator delegate. Additional parameters specify options that modify the matching operation and a time-out interval if no match is found.

Syntax

[System.MonoTODO("Timeouts are ignored.")]
public static string Replace (string input, string pattern, MatchEvaluator evaluator, RegexOptions options, TimeSpan matchTimeout)

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 enumeration values that provide options for matching.
matchTimeout
A time-out interval, or Regex.InfiniteMatchTimeout to indicate that the method should not time out.

Returns

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.

Remarks

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

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

  • If the replacement string results from some processing performed on the matched string.

  • If 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 matchTimeout parameter specifies how long a pattern matching method should try to find a match before it times out. Setting a time-out interval prevents regular expressions that rely on excessive backtracking from appearing to "stop responding when they process input that contains near matches. For more information, see Best Practices for Regular Expressions in the .NET Framework and Backtracking. If no match is found in that time interval, the method throws a System.Text.RegularExpressions.RegexMatchTimeoutException exception. matchTimeout overrides any default time-out value defined for the application domain in which the method executes.

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: 4.0.0.0