How to validate domain name using regex?

Question

This is my code for validating domain name.

function frmValidate() {
    var val = document.frmDomin;
    if (/^[a-zA-Z0-9][a-zA-Z0-9-]{1,61}[a-zA-Z0-9]\.[a-zA-Z]{2,}$/.test(val.name.value)) {
    }
    else {
        alert("Enter Valid Domain Name");
        val.name.focus();
        return false;
    }
}

and

<form name="frmDomin" action="" method="post" onsubmit="return frmValidate();">
Domain Name : <input type="text" value="" id="name" name="name"  />
</form>

Now I entered http://devp1.tech.in and it alert the message. I want to enter sub domain also. How to change this? I should not get alert.

if you want to validate only the domain names then why are you passing `http://`? — Avinash Raj, Sep 29 '14 at 06:21
Including `http://` makes it a [URI](https://en.wikipedia.org/wiki/Uniform_resource_identifier), not just a domain/host name. — Jonathan Lonowski, Sep 29 '14 at 06:21
Two immediate problems that I can see: no support for .co.uk (or subdomains, which your question is about) but also two consecutive hyphens is only valid as part of an IDN. — Niet the Dark Absol, Sep 29 '14 at 06:25
You need to add a dot iniside the character class. `^[a-zA-Z0-9][a-zA-Z0-9-.]{1,61}[a-zA-Z0-9]\.[a-zA-Z]{2,}$` — Avinash Raj, Sep 29 '14 at 06:27
@AvinashRaj that regex allow two dots in a row for subdomains, like subdomain..google.es. Can you fix it ? — Héctor León, Jun 20 '16 at 13:32

score 44 · Accepted Answer · edited Feb 10 '23 at 23:13

44

Try this:

^[a-zA-Z0-9][a-zA-Z0-9-]{0,61}[a-zA-Z0-9](?:\.[a-zA-Z]{2,})+$

Demo

edited Feb 10 '23 at 23:13

Alex Gyoshev

11,929
4
44
74

answered Sep 29 '14 at 06:21

walid toumi

2,172
1
13
10

Can you update this answer to also allow subdomains ? – Héctor León Jun 20 '16 at 14:03
3

Something missing here, It doesn't match `www.test2.com` but it does match `test2.com`. – yeya Nov 05 '16 at 20:40
it does not test for domain in numbers like 192.168.3.1 – test_124 Apr 17 '18 at 07:58
1

In my implementation of this answer, it worked as `/^[a-zA-Z0-9][a-zA-Z0-9-]{1,61}[a-zA-Z0-9](?:\.[a-zA-Z]{2,})+/` regex – Abel Callejo Dec 26 '18 at 15:56
Why aren't underscores included in regex? – Miguel Mota Jan 28 '20 at 22:45
@MiguelMota Underscore is no allowed characters in domain names. – Mecki Nov 12 '21 at 14:43
1

This regex does not work correctly. It should match all samples given here except the last one which is no valid domain: https://regex101.com/r/Vi2CYC/1 But it fails to match 3 valid domains and does match the invalid one at the end. For comparison, this one works as expected: https://regex101.com/r/d7YuFt/1 – Mecki Nov 12 '21 at 22:13
1

This also fails for single-letter domains, i.e. `a.co`, but those are valid. – J23 May 25 '22 at 21:36

Lux · Answer 2 · 2020-07-10T06:48:01.050

This is a little on the heavy side:

^(?:(?:(?:[a-zA-z\-]+)\:\/{1,3})?(?:[a-zA-Z0-9])(?:[a-zA-Z0-9\-\.]){1,61}(?:\.[a-zA-Z]{2,})+|\[(?:(?:(?:[a-fA-F0-9]){1,4})(?::(?:[a-fA-F0-9]){1,4}){7}|::1|::)\]|(?:(?:[0-9]{1,3})(?:\.[0-9]{1,3}){3}))(?:\:[0-9]{1,5})?$

Will match:

google.com
db.my-website.co.us
ftp://container-617.databases.online
many-ports.com:7777

Note: will not match localhost

IPv4

192.168.3.1
127.0.0.1:3306

IPv6 (partial support)

[2001:0db8:85a3:0000:0000:8a2e:0370:7334]
[2001:db8:85a3:0:0:8a2e:370:7334] (same as previous)
[da7a:ba5e:da7a:ba5e:da7a:ba5e:da7a:ba5e]:3306
[::1] (localhost loopback)
[::] (unspecified address)

But not (IPv6)

[2001:db8:85a3::8a2e:370:7334]

This regular expression does not support collapsing consecutive 0-segments into a '::' in IPv6 addresses. (read: don't try this on IPv6 addresses)

2 letter domains such as `ti.com` do not work with this regex. — James Anderson Jr., Jul 04 '20 at 23:45
@JamesAndersonJr.Should be fixed? In all honesty, I'm no longer 100% sure what most of that regex does anyway... — Lux, Jul 10 '20 at 06:48

score 11 · Answer 3 · answered Jul 15 '20 at 14:18

I'd advise reading up on O'Reilly's guide: https://www.oreilly.com/library/view/regular-expressions-cookbook/9781449327453/ch08s15.html

Try using https://regex101.com/ to validate the results of your regex.

8.15. Validating Domain Names Problem You want to check whether a string looks like it may be a valid, fully qualified domain name, or find such domain names in longer text.

Solution Check whether a string looks like a valid domain name:
^([a-z0-9]+(-[a-z0-9]+)*\.)+[a-z]{2,}$
Regex options: Case insensitive Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python
\A([a-z0-9]+(-[a-z0-9]+)*\.)+[a-z]{2,}\Z
Regex options: Case insensitive Regex flavors: .NET, Java, PCRE, Perl, Python, Ruby Find valid domain names in longer text:
\b([a-z0-9]+(-[a-z0-9]+)*\.)+[a-z]{2,}\b
Regex options: Case insensitive Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby Check whether each part of the domain is not longer than 63 characters:
\b((?=[a-z0-9-]{1,63}\.)[a-z0-9]+(-[a-z0-9]+)*\.)+[a-z]{2,63}\b
Regex options: Case insensitive Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby Allow internationalized domain names using the punycode notation:
\b((xn--)?[a-z0-9]+(-[a-z0-9]+)*\.)+[a-z]{2,}\b
Regex options: Case insensitive Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby Check whether each part of the domain is not longer than 63 characters, and allow internationalized domain names using the punycode notation:
\b((?=[a-z0-9-]{1,63}\.)(xn--)?[a-z0-9]+(-[a-z0-9]+)*\.)+[a-z]{2,63}\b
Regex options: Case insensitive Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby

Discussion A domain name has the form of domain.tld, or subdomain.domain.tld, or any number of additional subdomains. ...

score 1 · Answer 4 · edited Sep 21 '17 at 13:03

<script>
    function frmValidate() {
        var val = document.frmDomin.name.value;
        if (/^[a-zA-Z0-9][a-zA-Z0-9-]{1,61}[a-zA-Z0-9](?:\.[a-zA-Z]{2,})+$/.test(val)) {
            alert("Valid Domain Name");
            return true;
        } else {
            alert("Enter Valid Domain Name");
            val.name.focus();
            return false;
        }
    }
</script>

Note : This will not validate Url.

Mogli · Answer 5 · 2014-09-29T06:29:11.820

0

Try this regex:

/([a-z0-9]+\.)*[a-z0-9]+\.[a-z]+/

edited Sep 29 '14 at 06:29

answered Sep 29 '14 at 06:19

Mogli

27
3

How to validate domain name using regex?

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