Regular Expressions (RegEx) in C#

What is Regular Expressions (RegEx) in C#?

Regular Expressions (RegEx) in C# provide a powerful way to perform pattern matching and text processing. It is commonly used for tasks like input validation, searching, and replacing text.

Key Features of Regular Expressions

• Provides a powerful pattern-matching mechanism.
• Useful for text validation, searching, and replacing.
• Implemented using the System.Text.RegularExpressions namespace.
• Supports predefined character classes and quantifiers.

Example: Basic RegEx Usage

The following example demonstrates how to check if a string contains a valid email format.

Example: Validating an Email Address

using System;
using System.Text.RegularExpressions;

class Program
{
    static void Main()
    {
        string email = "example@domain.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 Regex.IsMatch() method checks if the email string matches the pattern.

Common RegEx Patterns

Below are some commonly used regular expressions for validation:

Using RegEx for Searching and Replacing

Regular expressions can be used to search for patterns and replace text dynamically.

Example: Replacing Text with RegEx

using System;
using System.Text.RegularExpressions;

class Program
{
    static void Main()
    {
        string text = "The quick brown fox jumps over the lazy dog.";
        string pattern = @"\bfox\b";
        string replacement = "cat";

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

// Output:
// The quick brown cat jumps over the lazy dog.
        

The Regex.Replace() method replaces occurrences of "fox" with "cat" in the given text.

Extracting Data Using RegEx

The Regex.Matches() method can be used to extract specific data from a text.

Example: Extracting Phone Numbers

using System;
using System.Text.RegularExpressions;

class Program
{
    static void Main()
    {
        string text = "Contact us at 9876543210 or 1234567890.";
        string pattern = @"\b\d{10}\b";

        MatchCollection matches = Regex.Matches(text, pattern);

        foreach (Match match in matches)
        {
            Console.WriteLine($"Phone Number: {match.Value}");
        }
    }
}

// Output:
// Phone Number: 9876543210
// Phone Number: 1234567890
        

The Regex.Matches() method extracts all 10-digit phone numbers from the given text.

When to Use Regular Expressions?

• For input validation (e.g., emails, phone numbers, passwords).
• To search and extract patterns from text.
• For replacing text dynamically in large data sets.
• To clean and format text efficiently.