Regular Expressions in C Sharp Language

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dia.org/wiki/C_Sharp_(programming_language)">C#, regular expressions are supported through the System.Text.RegularExpressions namespace, and they provide a versatile way to search, match, and manipulate text data. This post will introduce you to the basics of using regular expressions in C# with practical examples.

Getting Started

Before we dive into examples, make sure you have the System.Text.RegularExpressions namespace included in your project by adding the following line at the top of your C# file:

using System.Text.RegularExpressions;

Creating a Regular Expression

In C#, you create a regular expression by instantiating the Regex class, which allows you to define a pattern to search for in a string. Here’s an example of creating a simple regex to match an email address:

string pattern = @"[\w-]+(\.[\w-]+)*@[\w-]+(\.[\w-]+)+";
Regex regex = new Regex(pattern);

In this example, we’ve defined a regex pattern that matches a typical email address.

Matching with Regular Expressions

To search for and extract text that matches your regular expression, you can use the Match method. Here’s how you would use it with the email regex:

string text = "Contact us at support@example.com or info@example.org";
MatchCollection matches = regex.Matches(text);

foreach (Match match in matches)
{
    Console.WriteLine("Match found: " + match.Value);
}

In this code, the Matches method finds all matches in the input string, and we iterate through the MatchCollection to print out the matched email addresses.

Extracting Groups

Regular expressions allow you to define groups within your patterns. You can use these groups to extract specific parts of the matched text. Let’s modify our email regex example to capture the username and domain separately:

string pattern = @"(?<username>[\w-]+)(@)(?<domain>[\w-]+(\.[\w-]+)+)";
Regex regex = new Regex(pattern);
MatchCollection matches = regex.Matches(text);

foreach (Match match in matches)
{
    string username = match.Groups["username"].Value;
    string domain = match.Groups["domain"].Value;
    Console.WriteLine("Username: " + username);
    Console.WriteLine("Domain: " + domain);
}

In this code, we use named groups to extract the username and domain from each email address.

Replacing with Regular Expressions

Regular expressions in C# are also useful for text replacement. You can use the Regex.Replace method to replace text that matches a pattern. Here’s an example:

string text = "My phone number is (123) 456-7890.";
string pattern = @"\(\d{3}\) \d{3}-\d{4}";
string replacement = "###-###-####";

string result = Regex.Replace(text, pattern, replacement);
Console.WriteLine("Modified text: " + result);

In this example, we replace a phone number with a generic format (###-###-####).