Regex for extracting second level domain from FQDN?
asp.net-mvc, vb.net
Solution
I used this Regex successfully to match "example.com" from your list of test cases.
"(?<hostname>(\w+\.)*)(?<domainname>(\w+\.\w+))"
The dot character (".") needs to escaped as "\.". The "." character in a regex pattern matches any character.
Also the regex pattern you provided requires that there be 1 or more word characters followed by a dot before the domainname match (this part "(?(\w+))." of the pattern. Also, I'm assuming that the . character was supposed to be escaped). This fails to make a match for the input "example.com" because there's no word character and dot before the domainname match.
I changed the pattern so that the hostname match would have zero or more matches of "1 or more word characters followed by a dot". This will match "foo" in "foo.example.com" and "foo.bar" in "foo.bar.example.com".
Problem
I can't figure this out. I need to extract the second level domain from a FQDN. For example, all of these need to return "example.com": - example.com - foo.example.com - bar.foo.example.com - example.com:8080 - foo.example.com:8080 - bar.foo.example.com:8080 Here's what I have so far: ``` Dim host = Request.Headers("Host") Dim pattern As String = "(?<hostname>(\w+)).(?<domainname>(\w+.\w+))" Dim theMatch = Regex.Match(host, pattern) ViewData("Message") = "Domain is: " + theMatch.Groups("domainname").ToString ``` It fails for `example.com:8080` and `bar.foo.example.com:8080`. Any ideas?