Regex for getting domain and subdomain in C#

Question

I am having a requirement to correctly get the domain/subdomain based on the current url. this is required in order to correctly fetch the data from database and further call web api with correct parameters.

In perticular, I am facing issues with local and production urls. for ex.

In local, i have

http://sample.local.example.com 
http://test.dev.example.com

In production, i have

http://client.example.com 
http://program.live.example.com

i need

Subdomain as: sample / test / client / program
Domain as: exmpale

So far i tried to use c# with following code to identify the same. It works fine on my local but i am sure this will create an issue on production at some point of time. Basically, for Subdomain, get the first part and for Domain, get the last part before ''.com''

 var host = Request.Url.Host;
 var domains = host.Split('.');
 var subDomain = domains[0];
 string mainDomain = string.Empty;
  #if DEBUG
    mainDomain = domains[2]; 
  #else
    mainDomain = domains[1]; 
  #endif

 return Tuple.Create(mainDomain, subDomain);

so for the subdomain you want only `sample´ ? without the `http://` ? and for the production the value would be `client` ? — Mong Zhu, Sep 07 '18 at 09:25
Try `^https?://(\w+)?\S*\.(\w+)\.\w+$`. See live demo here https://regex101.com/r/80KxB6/1 — revo, Sep 07 '18 at 09:41

aloisdg · Accepted Answer · 2021-10-30T08:50:41.180

6

Instead of a regex, I think Linq should help your here. Try:

public static (string, string) GetDomains(Uri url)
{
    var domains = url.Host.Substring(0, url.Host.LastIndexOf(".")).Split('.');
    var subDomain = string.Join("/", domains.Take(domains.Length - 1));
    var mainDomain = domains.Last();
    return (mainDomain, subDomain);
}

output for "http://program.live.example.com"

example
program/live

Try it Online!

edited Oct 30 '21 at 08:50

answered Sep 07 '18 at 09:29

aloisdg

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2

marking this as answer because of the fact that it would be easy for the debugging. – patel.milanb Sep 07 '18 at 10:00
This will only work for top level domains (.com etc). Try it for a UK (.co.uk) website – Lee Smith Aug 17 '23 at 16:11

Mong Zhu · Answer 2 · 2018-09-07T10:29:17.990

2

This regex should work for you:

Match match = Regex.Match(temp, @"http://(\w+)\.?.*\.(\w+).com$");

string subdomain = match.Groups[1].Value;
string domain = match.Groups[2].Value;

http://(\w+)\. matches 1 or more word characters as group 1 before a dot and after http://

.* matches zero or more occurences of any character

\.(\w+).com matches 1 or more word characters as group 2 before .com and after a dot

$ specifies the end of the string

\.? makes the dot optional to catch the case if there is nothing between group 1 and 2 like in http://client.example.com

edited Sep 07 '18 at 10:29

answered Sep 07 '18 at 09:51

Mong Zhu

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@patel.milanb glad to hear – Mong Zhu Sep 07 '18 at 10:08

score 1 · Answer 3 · edited Jul 13 '19 at 22:58

1

You are doing the right and you can get the domain name as the second last value in the array.

var host = Request.Url.Host;
var domains = host.Split('.');
string subDomain = domains[0].Split('/')[2];
string mainDomain = domains[domains.Length-2];  
return Tuple.Create(mainDomain, subDomain);

If you want all the subdomains you can put a loop here.

edited Jul 13 '19 at 22:58

MarvMan

41
9

answered Sep 07 '18 at 10:09

Amit chauhan

540
9
22

Regex for getting domain and subdomain in C#

3 Answers3