How to Use Regex.IsMatch in C# for Pattern Matching

Use Regex.IsMatch(string input, string pattern) in C# to check if the input string matches the given regular expression pattern. It returns true if the pattern is found and false otherwise.

Syntax

The Regex.IsMatch method checks if a string matches a regular expression pattern.

• input: The string you want to test.
• pattern: The regular expression pattern to match.
• Returns true if the pattern matches anywhere in the input string; otherwise, false.

csharp

bool isMatch = Regex.IsMatch(input, pattern);

Example

This example shows how to check if a string contains only digits using Regex.IsMatch. It prints Match found! if the input matches the pattern.

csharp

using System;
using System.Text.RegularExpressions;

class Program
{
    static void Main()
    {
        string input = "12345";
        string pattern = "^\\d+$"; // Matches only digits from start to end

        bool isMatch = Regex.IsMatch(input, pattern);

        if (isMatch)
        {
            Console.WriteLine("Match found!");
        }
        else
        {
            Console.WriteLine("No match.");
        }
    }
}

Output

Match found!

Common Pitfalls

Common mistakes when using Regex.IsMatch include:

• Not escaping special characters in the pattern properly.
• Using patterns that match partially when full match is needed (use anchors like ^ and $).
• Confusing Regex.IsMatch with methods that return matched text.

Example of a wrong and right pattern:

csharp

using System;
using System.Text.RegularExpressions;

class Program
{
    static void Main()
    {
        string input = "abc123";

        // Wrong: pattern missing anchors, matches anywhere
        bool wrongMatch = Regex.IsMatch(input, "123");
        Console.WriteLine(wrongMatch); // True, but partial match

        // Right: pattern with anchors for full match
        bool rightMatch = Regex.IsMatch(input, "^abc123$");
        Console.WriteLine(rightMatch); // True, full match
    }
}

Output

True
True

Quick Reference

Tips for using Regex.IsMatch:

• Use ^ and $ to match the whole string.
• Escape special characters like \, ., ? in patterns.
• Use verbatim strings @"pattern" to avoid double escaping.
• Remember it returns a boolean, not the matched text.

Key Takeaways

Regex.IsMatch returns true if the input string matches the given pattern anywhere.

Use anchors ^ and $ to ensure the entire string matches the pattern.

Escape special regex characters properly or use verbatim strings for patterns.

Regex.IsMatch only tells if a match exists; it does not return the matched text.

Common mistakes include missing anchors and incorrect escaping.