using System;

using System.Text.RegularExpressions;

public class Program

{

    public static void Main()

    {

        string input = "This {is} a {test}...";

        string output = Test(input);

        Console.WriteLine(output);

    }

    private static readonly Regex Pattern = new Regex("{(.+?)}", RegexOptions.Compiled);

​

    public static string Test(string input)

    {

        return Pattern.Replace(input, match =>

        {

            string newMatch = match.Groups[1].Value;

            return ">> " + newMatch + " <<";

        });

    }

}