Odtnhj

I am using ipstack to get information about the user's IP. It gives me the hostname, but I would like to use the hostname to get the ISP. The hostname I am getting is:

d9687b05.cm-24.dynamic.ziggo.nl

Where I would like to extract the ziggo.nl <-- thats the ISP.

Of course it wont allways be ziggo, and it wont allways be .nl, so how would I go about getting that part of the hostname on different ones?

Without Regex and extra explanations it can be done in readable and comprehensible way ;)

var names = hostname.split(".");
var notRequired = Math.Max(0, names.Count() - 2);

var isp = string.Join(".", names.skip(notRequired));

Instead of using Regex I would do something like this:

string isp = "";
string split = hostname.Split('.');
int len = split.Length;
if(len >= 2)
 isp = $"split[len-2].split[len-1]";

Or this:

 string isp = "";
 string hostname = "d9687b05.cm-24.dynamic.ziggo.nl";
 int a = hostname.LastIndexOf(".");
 if(a>0)a=hostname.LastIndexOf(".", a-1);
 if(a!=-1) isp = hostname.Substring(a+1);

Live Demo

You can use this regex to capture the last two words,

.*.(w+.w+)

Demo

Explanation:

• 
  .*. --> Matches zero or more any character followed by a literal dot


• 
  (w+.w+) --> Matches one or more word char followed by literal dot followed by one or more word char

Here is a sample C# code,

 public static void Main(string args)
 
 var pattern = ".*\.(\w+\.\w+)";
 var match = Regex.Match("d9687b05.cm-24.dynamic.ziggo.nl", pattern);
 Console.WriteLine("DomainName: " + match.Groups[1].Value);
 

This gives following output,

DomainName: ziggo.nl