using System;

using System.Text.RegularExpressions;

public class Program

{

    public static void Main()

    {

        string[] keys = new string[] {

            "FOR TESTING/",

            "FOR TESTING/20220809-222-SUCAT.csv",

            "FOR TESTING/20220809-223-MARIKINA.csv"

        };

        Regex _regex = new Regex(

                pattern: "^[0-9]{8}-[0-9]{3}-\\w+.csv",

                options: RegexOptions.Compiled | RegexOptions.IgnoreCase);

        foreach(var s3Object in keys)

        {

            var idx = s3Object.LastIndexOfAny(new char[] { '\\', '/' }) + 1;

            if(idx >= 0 && _regex.IsMatch(s3Object, startat: idx))

            {

                Console.WriteLine($"{s3Object} is match ({s3Object[idx..]}).");

            } else {

                Console.WriteLine($"{s3Object} is not match ({s3Object[idx..]}).");

            }

        }

    }

}