Regex help - domain is not validating

Question

I am having a problem validating domains. What am I doing wrong?

        Regex re = new Regex("^[a-zA-Z0-9][a-zA-Z0-9-]{1,61}[a-zA-Z0-9]\\.[a-zA-Z]{2,}$");
        if (re.IsMatch(domain.Text))
//          if (Regex.IsMatch(domain.Text, @"^[a-zA-Z0-9][a-zA-Z0-9-]{1,61}[a-zA-Z0-9]\\.[a-zA-Z]{2,}$"))
            warningLabel.Text = "Domain format is invalid!";    // domain: " + domain.Text;

I checked with Regex checker and got "your pattern matches but there were no (capturing (groups)) in it that matched anything in the subject string."

Why I don't get errors on invalid characters?

Thank you.

I entered test,com - I expect this value to fail. However, it was always true. I realize now that I would have had (!re.IsMatch(...)) — Moshe Shmukler, Jan 09 '15 at 11:56

score 1 · Accepted Answer · edited May 23 '17 at 11:50

your Regex is basically correct (but see link below), and this test method confirms it:

public static void Test()
        {
            Regex re = new Regex("^[a-zA-Z0-9][a-zA-Z0-9-]{1,61}[a-zA-Z0-9]\\.[a-zA-Z]{2,}$");
            var m=re.Match("test.com");
            Console.WriteLine(m.Groups[0].Value);
            m=   re.Match("more-messy-domain-0234-example.xx");
            Console.WriteLine(m.Groups[0].Value);
       }

This outputs:

test.com

more-messy-domain0234-example.xx

Note there is a good discussion of regex for domain names here: Domain name validation with RegEx

There are some subtle situations which are not included in your regex.

Regex help - domain is not validating

1 Answers1