using System;

using System.Collections.Generic;   

using System.Text.RegularExpressions;

public class Program

{

    public static void Main()

    {

​

        string input =@"abc

def

abc

xyz

pop

mmm

091

abc";

        string[] replaces =  {"123","456","789"};

        Regex regEx = new Regex("abc");

        int index = 0;

        string result = regEx.Replace(input, delegate(Match match) {return replaces[index++];} );

        Console.WriteLine(result);

    }

}