using System;

using System.Linq;

​

// Purpose: see related StackOverflow topic:

// https://stackoverflow.com/a/44633997/1016343

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Sammy".TrimEnd("my"));

        Console.WriteLine("My o My".TrimEnd("My"));

        Console.WriteLine("My o My".TrimStart("My"));

        Console.WriteLine("moinmoin gibts gips? gips gibts moin".TrimStart("moin", false));

        Console.WriteLine("moinmoin gibts gips? gips gibts moin".TrimStart("moin", true).TrimEnd("moin").Trim());

    }

}

​

​

public static class Extension

{

    public static string TrimEnd(this string str, string trimStr, bool repeatTrim=false)

    {

        var strLen=str.Length;

        do

        {

            if (!str.EndsWith(trimStr)) return str;

            var spl = str.Split(new string[] { trimStr }, StringSplitOptions.None);

            str = string.Join(trimStr, spl, 0, spl.Count() - 1);

        } while (repeatTrim && strLen>str.Length);

        return str;

    }

    public static string TrimStart(this string str, string trimStr, bool repeatTrim=false)

    {

        var strLen = str.Length;

        do

        {

            if (!str.StartsWith(trimStr)) return str;

            var spl = str.Split(new string[] { trimStr }, 2, StringSplitOptions.None);

            str =  string.Join(trimStr, spl, 1, 1);

        } while (repeatTrim && strLen > str.Length);

        return str;

    }

}

​