named capture, C# - rextester

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//Title of this code
//Rextester.Program.Main is the entry point for your code. Don't change it.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;

namespace Rextester
{
    public class Program
    {
        public static void Main(string[] args)
        {
            string[] urls = {
                "https://download.my-domain.com/auth/login",
                "https://download.my-domain.com",
                "http://localhost:60162/API/script/authbar.js",
                "http://localhost:28173/logout.aspx",
                "http://my-domain.com/logout.aspx",
                "http://my-domain.com/logout.aspx/",
                "http://my-domain.com/",
                "http://my-domain.com",
                "http://my-domain.tk/",
                "http://my-domain.gov",
                "download.my-domain.com/auth/login",
                "www.download.my-domain.com/auth/login",
                "http://www.google.com",
                "https://www.google.com",
                "http://www.google.com/",
                "https://www.google.com/"
            };
            string p1 = @"[-a-z0-9_]+(?!://)(?:\.[-a-z0-9_\.]+)?(?=[/:]|$)";
            string p2 = @"(?:(https?://))?(?:((www\.)?))?(?<domain>([^[:/])+)";
            
            Regex r = new Regex(p2, RegexOptions.IgnoreCase);
            foreach(string url in urls)
            {
                Match m = r.Match(url);
                if (m.Success)
                    Console.WriteLine(m.Groups["domain"].Value);
            }
        }
    }
}

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Compilation time: 0.11 sec, absolute running time: 0.17 sec, cpu time: 0.12 sec, average memory usage: 18 Mb, average nr of threads: 5