using System;

using System.Text.RegularExpressions;

public class Program

{

    public static void Main()

    {

        string test = "test";

        Regex regex = new Regex(@"\\d{7}");

        Console.WriteLine(regex.Match(test));

        Console.WriteLine("test");

        Console.WriteLine(TryGetVesselImoFromFolder("test"));

        Console.WriteLine(TryGetVesselImoFromFolder("IMO 1234567"));

        Console.WriteLine(TryGetVesselImoFromFolder("IMO 12345678"));

        Console.WriteLine(TryGetVesselImoFromFolder("12345678"));

    }

        private static string TryGetVesselImoFromFolder(string folder) {

            if (folder.ToUpper().Contains("IMO")) {

​

            }

            Regex regex = new Regex(@"\\d{7}");

            Console.WriteLine(regex.Match(folder));

            return regex.IsMatch(folder) ? regex.Match(folder).Value : null;

        }

}