Replacing only numbers using Regex in C#

REGEX stands for Regular expression.
Using regex, we can replace the characters,numbers with a string (from 0-9)

Regex regex = new Regex("[Regular expression]");
output = regex.Replace("input_string", "substitution_string");

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;

namespace ConsoleApplication1
    class Program
        static void Main(string[] args)

            string filename = "My name is c-sharp 007; (got it !)";
            //find all characters that are letters
            Regex regex = new Regex("[0-9]");
            filename = regex.Replace(filename, "$");



My name is c-sharp $$$; (got it !)