How to validate a domain name using Regex & Php?

Question

I want a solution to validate only domain names not full urls, The following example is what i\'m looking for:

domain.com -> true
domain.net -> true
do         


        

Answer 1

In my case, domain name is considered as valid if the format is stackoverflow.com or xxx.stackoverflow.com

So in addition to other stack answers, I have added checking for www. also.

function isValidDomainName($domain) {
  if (filter_var(gethostbyname($domain), FILTER_VALIDATE_IP)) {
      return (preg_match('/^www./', $domain)) ? FALSE : TRUE;
  }
  return FALSE;
}

you can test the function with this code

    $domain = array("http://www.domain.com","http://www.domain.com/folder" ,"http://domain.com", "www.domain.com", "domain.com/subfolder", "domain.com","sub.domain.com");
    foreach ($domain as $v) {
        echo isValidDomainName($v) ? "{$v} is valid<br>" : "{$v} is invalid<br>";
    }

Answer 2

How about:

^(?:[-A-Za-z0-9]+\.)+[A-Za-z]{2,6}$

Answer 3

Please try this expression:

^(http[s]?\:\/\/)?((\w+)\.)?(([\w-]+)?)(\.[\w-]+){1,2}$

What it actually does

• optional http/s://
• optional www
• any valid alphanumeric name (including - and _)
• 1 or 2 occurrences of any valid alphanumeric name (including - and _)

Validation Examples

• http://www.test.com
• test.com.mt

Answer 4

Remember, regexes can only check to see if something is well formed. "www.idonotexistbecauseiammadeuponthespot.com" is well-formed, but doesn't actually exist... at the time of writing. ;) Furthermore, certain free web hosting providers (like Tripod) allow underscores in subdomains. This is clearly a violation of the RFCs, yet it sometimes works.

Do you want to check if the domain exists? Try dns_get_record instead of (just) a regex.

Answer 5

I made a function to validate the domain name without any regex.

<?php
function validDomain($domain) {
  $domain = rtrim($domain, '.');
  if (!mb_stripos($domain, '.')) {
    return false;
  }
  $domain = explode('.', $domain);
  $allowedChars = array('-');
  $extenion = array_pop($domain);
  foreach ($domain as $value) {
    $fc = mb_substr($value, 0, 1);
    $lc = mb_substr($value, -1);
    if (
      hash_equals($value, '')
      || in_array($fc, $allowedChars)
      || in_array($lc, $allowedChars)
    ) {
      return false;
    }
    if (!ctype_alnum(str_replace($allowedChars, '', $value))) {
      return false;
    }
  }
  if (
    !ctype_alnum(str_replace($allowedChars, '', $extenion))
    || hash_equals($extenion, '')
  ) {
    return false;
  }
  return true;
}
$testCases = array(
  'a',
  '0',
  'a.b',
  'google.com',
  'news.google.co.uk',
  'xn--fsqu00a.xn--0zwm56d',
  'google.com ',
  'google.com.',
  'goo gle.com',
  'a.',
  'hey.hey',
  'google-.com',
  '-nj--9*.vom',
  ' ',
  '..',
  'google..com',
  'www.google.com',
  'www.google.com/some/path/to/dir/'
);
foreach ($testCases as $testCase) {
  var_dump($testCase);
  var_dump(validDomain($TestCase));
  echo '<br /><br />';
}
?>

This code outputs:

string(1) "a" bool(false)

string(1) "0" bool(false)

string(3) "a.b" bool(true)

string(10) "google.com" bool(true)

string(17) "news.google.co.uk" bool(true)

string(23) "xn--fsqu00a.xn--0zwm56d" bool(true)

string(11) "google.com " bool(false)

string(11) "google.com." bool(true)

string(11) "goo gle.com" bool(false)

string(2) "a." bool(false)

string(7) "hey.hey" bool(true)

string(11) "google-.com" bool(false)

string(11) "-nj--9*.vom" bool(false)

string(1) " " bool(false)

string(2) ".." bool(false)

string(11) "google..com" bool(false)

string(14) "www.google.com" bool(true)

string(32) "www.google.com/some/path/to/dir/" bool(false)

I hope I have covered everything if I missed something please tell me and I can improve this function. :)

Answer 6

The accepted answer is incomplete/wrong.

The regex pattern;

• should NOT validate domains such as:
  -domain.com, domain--.com, -domain-.-.com, domain.000, etc...

• should validate domains such as:
  schools.k12, newTLD.clothing, good.photography, etc...

After some further research; below is the most correct, cross-language and compact pattern I could come up with:

^(?!\-)(?:(?:[a-zA-Z\d][a-zA-Z\d\-]{0,61})?[a-zA-Z\d]\.){1,126}(?!\d+)[a-zA-Z\d]{1,63}$

This pattern conforms with most* of the rules defined in the specs:

• Each label/level (splitted by a dot) may contain up to 63 characters.
• The full domain name may have up to 127 levels.
• The full domain name may not exceed the length of 253 characters in its textual representation.
• Each label can consist of letters, digits and hyphens.
• Labels cannot start or end with a hyphen.
• The top-level domain (extension) cannot be all-numeric.

Note 1: The full domain length check is not included in the regex. It should be simply checked by native methods e.g. strlen(domain) <= 253.
Note 2: This pattern works with most languages including PHP, Javascript, Python, etc...

See DEMO here (for JS, PHP, Python)

More Info:

• The regex above does not support IDNs.

• There is no spec that says the extension (TLD) should be between 2 and 6 characters. It actually supports 63 characters. See the current TLD list here. Also, some networks do internally use custom/pseudo TLDs.

• Registration authorities might impose some extra, specific rules which are not explicitly supported in this regex. For example, .CO.UK and .ORG.UK must have at least 3 characters, but less than 23, not including the extension. These kinds of rules are non-standard and subject to change. Do not implement them if you cannot maintain.

• Regular Expressions are great but not the best effective, performant solution to every problem. So a native URL parser should be used instead, whenever possible. e.g. Python's urlparse() method or PHP's parse_url() method...

• After all, this is just a format validation. A regex test does not confirm that a domain name is actually configured/exists! You should test the existence by making a request.

Specs & References:

• IETF: RFC1035
• IETF: RFC1123
• IETF: RFC2181
• IETF: RFC952
• Wikipedia: Domain Name System

UPDATE (2019-12-21): Fixed leading hyphen with subdomains.