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C# Regex.Replace Examples: MatchEvaluatorUse Regex.Replace and MatchEvaluator to manipulate strings based on patterns.
Regex.Replace. This C# method processes text replacements. It handles simple and complex replacements. For complex patterns, we use a MatchEvaluator delegate to encode the logic.
Method details. To learn how to use Regex.Replace, we change a string with lowercased words to have uppercased ones. But many other replacements can be done.
Regex
First example. This program uses the Regex.Replace static method with a string replacement. It is possible to specify a delegate of type MatchEvaluator for more complex replacements.
Pattern We use a pattern to replace all 3-letter sequences starting and ending with certain letters with a replacement string.
Tip The Regex method allows you to replace variations in the string in one statement.
C# program that uses Regex.Replace method
using System; using System.Text.RegularExpressions; class Program { static void Main() { // Input string. string input = "abc def axc"; Console.WriteLine(input); // Use Regex.Replace to replace the pattern in the input. string output = Regex.Replace(input, @"a..", "CHANGED"); Console.WriteLine(output); } }
abc def axc CHANGED def CHANGED
a First letter starts with lowercase a. .. Two characters of any kind.
MatchEvaluator. We can specify a MatchEvaluator. This is a delegate method that the Regex.Replace method calls to modify the match. Here we use MatchEvaluator to uppercase matches.
Delegates
String You can use Regex.Replace for simple replacements by using a string argument. For complex replacements, use MatchEvaluator.
UpperFirst In Regex.Replace, we use the delegate syntax for a method that alters strings to have an uppercase first letter.
Tip Delegate methods are methods you can use as variables and parameters. They introduce some syntactic complexity.
C# program that capitalizes strings
using System; using System.Text.RegularExpressions; class Program { static void Main() { // Input strings. const string s1 = "marcus aurelius"; const string s2 = "the golden bowl"; const string s3 = "Thomas jefferson"; // Write output strings. Console.WriteLine(TextTools.UpperFirst(s1)); Console.WriteLine(TextTools.UpperFirst(s2)); Console.WriteLine(TextTools.UpperFirst(s3)); } } public static class TextTools { /// <summary> /// Uppercase first letters of all words in the string. /// </summary> public static string UpperFirst(string s) { return Regex.Replace(s, @"\b[a-z]\w+", delegate(Match match) { string v = match.ToString(); return char.ToUpper(v[0]) + v.Substring(1); }); } }
Marcus Aurelius The Golden Bowl Thomas Jefferson
\b Word break: Matches where a word starts. [a-z] Matches any lowercase ASCII letter. We only need to match words with lowercase first letters. This is a character range expression. \w+ Word characters: Matches must have one or more characters.
Other uses. Microsoft indicates we can use MatchEvaluator to perform validation. We can use it "to perform custom verifications or operations at each Replace operation."
Tip To enhance this capitalization algorithm, you could store a Dictionary of words that need special-casing.
However This requires a bit of manual work to find most of the names using different rules.
A summary. Regex.Replace can be used in 2 ways. The MatchEvaluator delegate offers a high degree of control. With a string, the Regex.Replace method can be used for simpler tasks.
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