Regex.Replace Method (String, MatchEvaluator, Int32)
In a specified input string, replaces a specified maximum number of strings that match a regular expression pattern with a string returned by a MatchEvaluator delegate.
Assembly: System (in System.dll)
Public Function Replace ( input As String, evaluator As MatchEvaluator, count As Integer ) As String
The string to search for a match.
A custom method that examines each match and returns either the original matched string or a replacement string.
The maximum number of times the replacement will occur.
Return ValueType: 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 the regular expression pattern is not matched in the current instance, the method returns the current instance unchanged.
Themethod is useful for replacing a regular expression match 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 regular expression is the pattern defined by the constructor for the current Regex object.
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.
Your custom method returns a string that replaces the matched input.
The RegexMatchTimeoutException exception is thrown if the execution time of the replacement operation exceeds the time-out interval specified by the Regex.Regex(String, RegexOptions, TimeSpan) constructor. If you do not set a time-out interval when you call the constructor, the exception is thrown if the operation exceeds any time-out value established for the application domain in which the Regex object is created. If no time-out is defined in the Regex constructor call or 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 deliberately misspell half of the words in a list. It uses the regular expression \w*(ie|ei)\w* to match words that include the characters "ie" or "ei". It passes the first half of the matching words to the ReverseLetter method, which, in turn, uses the Replace(String, String, String, RegexOptions) method to reverse "i" and "e" in the matched string. The remaining words remain unchanged.
Imports System.Text.RegularExpressions Module Example Public Sub Main() Dim input As String = "deceive relieve achieve belief fierce receive" Dim pattern As String = "\w*(ie|ei)\w*" Dim rgx As New Regex(pattern, RegexOptions.IgnoreCase) Console.WriteLine("Original string: " + input) Dim result As String = rgx.Replace(input, AddressOf ReverseLetter, input.Split(" "c).Length \ 2) Console.WriteLine("Returned string: " + result) End Sub Public Function ReverseLetter(match As Match) As String Return Regex.Replace(match.Value, "([ie])([ie])", "$2$1", RegexOptions.IgnoreCase) End Function End Module ' The example displays the following output: ' Original string: deceive relieve achieve belief fierce receive ' Returned string: decieve releive acheive belief fierce receive
Available since 8
Available since 1.1
Portable Class Library
Supported in: portable .NET platforms
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Available since 8.1