Here is a simple example using C# to extract the various parts of a URL.

Code-Behind

        protected void Page_Load(object sender, EventArgs e)
        {
            // debug
            Response.Write(string.Format("{0}: {1}<br />", "Protocol", Request.Protocol()));
            Response.Write(string.Format("{0}: {1}<br />", "Host", Request.Host()));
            Response.Write(string.Format("{0}: {1}<br />", "SubDomains", string.Join(".", Request.SubDomains())));
            Response.Write(string.Format("{0}: {1}<br />", "SubDomain", Request.SubDomain()));
            Response.Write(string.Format("{0}: {1}<br />", "Domain", Request.Domain()));
            Response.Write(string.Format("{0}: {1}<br />", "BaseUrl", Request.BaseUrl()));
            Response.Write(string.Format("{0}: {1}<br />", "RawUrl", Request.RawUrl));
            Response.Write(string.Format("{0}: {1}<br />", "AbsoluteUri", Request.Url.AbsoluteUri));
            Response.Write(string.Format("{0}: {1}<br />", "AbsolutePath", Request.Url.AbsolutePath));
            Response.Write(string.Format("{0}: {1}<br />", "FileName", Path.GetFileName(Request.Url.AbsolutePath)));
            Response.Write(string.Format("{0}: {1}<br />", "VirtualPath", VirtualPathUtility.ToAbsolute("~/")));
            Response.Write(string.Format("{0}: {1}<br />", "UrlHttps", Request.UrlHttps()));
            Response.Write(string.Format("{0}: {1}<br />", "UrlHttp", Request.UrlHttp()));
            Response.Write(string.Format("{0}: {1}<br />", "PageName v1", Request.PageName()));
            Response.Write(string.Format("{0}: {1}<br />", "PageName v2", Request.PageName(IncludeExtension: true)));
        }

Extensions

        // e.g. https
        public static string Protocol(this HttpRequest Request)
        {
            return Request.Url.Scheme;
        }

        // e.g. pavey.azurewebsites.net
        public static string Host(this HttpRequest Request)
        {
            return Request.Url.Host.ToLower();
        }

        // e.g. https://pavey.azurewebsites.net/debug/?x=1&y=2
        public static string UrlHttps(this HttpRequest Request)
        {
            return string.Format("https://{0}{1}", Request.Host(), Request.RawUrl);
        }

        // e.g. http://pavey.azurewebsites.net/debug/?x=1&y=2
        public static string UrlHttp(this HttpRequest Request)
        {
            return string.Format("http://{0}{1}", Request.Host(), Request.RawUrl);
        }

        // e.g. true if value is formatted as a valid IPv4 address
        public static bool IsValidIPAddress(this string Value)
        {
            return Regex.Match(Value, "\\b(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\\b").Success;
        }

        // e.g. true if testing using an IP address instead of a fully qualified host name
        public static bool IsIPAddress(this HttpRequest Request)
        {
            return Request.Host().IsValidIPAddress();
        }

        // e.g. true if testing using localhost
        public static bool IsLocalHost(this HttpRequest Request)
        {
            return Request.Host().ToLower().Equals("localhost");
        }

        // e.g. dev.www
        public static List SubDomains(this HttpRequest Request)
        {
            // variables
            string[] MyArray = Request.Host().Split(".".ToCharArray());
            List MySubDomains = new List();

            // make sure this is not an ip address
            if (Request.IsIPAddress())
            {
                return MySubDomains;
            }

            // make sure we have all the parts necessary
            if (MyArray == null)
            {
                return MySubDomains;
            }

            // last part is the tld (e.g. .com)
            // second to last part is the domain (e.g. mydomain)
            // the remaining parts are the sub-domain(s)
            if (MyArray.Length > 2)
            {
                for (int i = 0; i <= MyArray.Length - 3; i++)
                {
                    MySubDomains.Add(MyArray[i]);
                }
            }

            // return
            return MySubDomains;
        }

        // e.g. www
        public static string SubDomain(this HttpRequest Request)
        {
            if (Request.SubDomains().Count > 0)
            {
                // handle cases where multiple sub-domains (e.g. dev.www)
                return Request.SubDomains().Last();
            }
            else
            {
                // handle cases where no sub-domains
                return string.Empty;
            }
        }

        // e.g. azurewebsites.net
        public static string Domain(this HttpRequest Request)
        {
            // variables
            string[] MyArray = Request.Host().Split(".".ToCharArray());

            // make sure this is not an ip address
            if (Request.IsIPAddress())
            {
                return string.Empty;
            }

            // special case for localhost
            if (Request.IsLocalHost())
            {
                return Request.Host().ToLower();
            }

            // make sure we have all the parts necessary
            if (MyArray == null)
            {
                return string.Empty;
            }

            // make sure we have all the parts necessary
            if (MyArray.Length > 1)
            {
                return string.Format("{0}.{1}", MyArray[MyArray.Length - 2], MyArray[MyArray.Length - 1]);
            }

            // return empty string
            return string.Empty;
        }

        // e.g. https://pavey.azurewebsites.net/
        public static string BaseUrl(this HttpRequest Request)
        {
            // variables
            string Authority = Request.Url.GetLeftPart(UriPartial.Authority).TrimStart('/').TrimEnd('/');
            string ApplicationPath = Request.ApplicationPath.TrimStart('/').TrimEnd('/');

            // add trailing slashes if necessary
            if (Authority.Length > 0)
            {
                Authority += "/";
            }

            if (ApplicationPath.Length > 0)
            {
                ApplicationPath += "/";
            }

            // return
            return string.Format("{0}{1}", Authority, ApplicationPath);
        }

        // e.g. default, default.aspx
        public static string PageName(this HttpRequest Request, bool IncludeExtension = false, bool IncludeQueryString = false)
        {
            // variables
            string AbsolutePath = Request.Url.AbsolutePath;
            string PageName = Path.GetFileName(AbsolutePath);
            string Extension = Path.GetExtension(AbsolutePath);
            string QueryString = Request.QueryString.ToString();

            // remove extension
            if (!IncludeExtension && !IncludeQueryString && PageName.HasValue())
            {
                PageName = PageName.Replace(Extension, string.Empty);
            }

            // include querystring
            if (IncludeQueryString && PageName.HasValue() && QueryString.HasValue())
            {
                PageName = string.Format("{0}?{1}", PageName, QueryString);
            }

            // return
            return PageName;
        }

Click here to see a demo with sample output.

Matt Pavey is a Microsoft Certified software developer who specializes in ASP.Net, VB.Net, C#, AJAX, LINQ, XML, XSL, Web Services, SQL, jQuery, and more. Follow on Twitter @matthewpavey