Methods for Regular Expressions in C#

The Regex class in C# provides various methods to work with regular expressions, enabling pattern matching, searching, replacing, and extracting specific data.

Commonly Used Regular Expression Methods

Below are some essential methods provided by the Regex class:

Method	Description	Example Usage
`IsMatch()`	Checks if a string matches a given pattern.	`Regex.IsMatch("abc123", @"\d+")` → Returns true
`Match()`	Finds the first match of a pattern in a string.	`Regex.Match("abc123", @"\d+")` → Returns "123"
`Matches()`	Finds all matches of a pattern in a string.	`Regex.Matches("a1b2c3", @"\d")` → Returns "1", "2", "3"
`Replace()`	Replaces matching text with a new value.	`Regex.Replace("hello 123", @"\d+", "*")` → Returns "hello *"
`Split()`	Splits a string based on a pattern.	`Regex.Split("apple,banana,grape", @",")` → Returns "apple", "banana", "grape"

Example: Checking if a String Matches a Pattern

The following example demonstrates how to use IsMatch() to validate an email address.

Example: Validating an Email with `IsMatch()`

using System;
using System.Text.RegularExpressions;

class Program
{
    static void Main()
    {
        string email = "user@example.com";
        string pattern = @"^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$";

        bool isValid = Regex.IsMatch(email, pattern);
        Console.WriteLine($"Is Valid Email: {isValid}");
    }
}

// Output:
// Is Valid Email: True

The IsMatch() method checks if the provided email matches the pattern.

Example: Extracting a Phone Number from Text

The following example demonstrates how to extract a phone number using Match().

Example: Extracting a Phone Number with `Match()`

using System;
using System.Text.RegularExpressions;

class Program
{
    static void Main()
    {
        string text = "Contact: 9876543210";
        string pattern = @"\b\d{10}\b";

        Match match = Regex.Match(text, pattern);
        Console.WriteLine($"Extracted Phone Number: {match.Value}");
    }
}

// Output:
// Extracted Phone Number: 9876543210

The Match() method finds the first 10-digit number in the text.

Example: Replacing Digits in a String

The following example demonstrates how to replace digits with asterisks using Replace().

Example: Masking Numbers with `Replace()`

using System;
using System.Text.RegularExpressions;

class Program
{
    static void Main()
    {
        string text = "Order ID: 12345";
        string pattern = @"\d";

        string result = Regex.Replace(text, pattern, "*");
        Console.WriteLine(result);
    }
}

// Output:
// Order ID: *****

The Replace() method replaces all digits in the string with asterisks.

When to Use Regular Expression Methods?

Use IsMatch() for validation (e.g., email, phone number).
Use Match() to extract the first occurrence of a pattern.
Use Matches() to retrieve all occurrences of a pattern.
Use Replace() to substitute matching text.
Use Split() to break a string into an array based on a pattern.

Methods for Regular Expressions in C#