using System;

using System.Linq;

using System.Text.RegularExpressions;

public class Program

{

    public static void Main()

    {

        string input = @"^en/resources/case-studies/

^/resources/case-studies/

^en/resources/case studies/

^/resources/case studies/";

        string output = Test(input);

        Console.WriteLine(output);

    }

    private static readonly Regex Pattern = new Regex(@"\^(en)?/resources/case(-|\s)studies/", RegexOptions.Compiled);

​

    public static string Test(string input)

    {

        var matches = Pattern.Matches(input);

        return String.Join("\r\n", matches.Cast<Match>().Select(m => m.Value).ToArray());

    }

}