How to validate domain name in PHP?

user_95944 0
Viewed 118712

Is it possible without using regular expression?

For example, I want to check that a string is a valid domain:

domain-name
abcd
example

Are valid domains. These are invalid of course:

domaia@name
ab$%cd

And so on. So basically it should start with an alphanumeric character, then there may be more alnum characters plus also a hyphen. And it must end with an alnum character, too.

If it's not possible, could you suggest me a regexp pattern to do this?

EDIT:

Why doesn't this work? Am I using preg_match incorrectly?

$domain = '@djkal';
$regexp = '/^[a-zA-Z0-9][a-zA-Z0-9\-\_]+[a-zA-Z0-9]$/';
if (false === preg_match($regexp, $domain)) {
    throw new Exception('Domain invalid');
}
domain-name php regex
20 Answers
<?php
function is_valid_domain_name($domain_name)
{
    return (preg_match("/^([a-z\d](-*[a-z\d])*)(\.([a-z\d](-*[a-z\d])*))*$/i", $domain_name) //valid chars check
            && preg_match("/^.{1,253}$/", $domain_name) //overall length check
            && preg_match("/^[^\.]{1,63}(\.[^\.]{1,63})*$/", $domain_name)   ); //length of each label
}
?>

Test cases:

is_valid_domain_name? [a]                       Y
is_valid_domain_name? [0]                       Y
is_valid_domain_name? [a.b]                     Y
is_valid_domain_name? [localhost]               Y
is_valid_domain_name? [google.com]              Y
is_valid_domain_name? [news.google.co.uk]       Y
is_valid_domain_name? [xn--fsqu00a.xn--0zwm56d] Y
is_valid_domain_name? [goo gle.com]             N
is_valid_domain_name? [google..com]             N
is_valid_domain_name? [google.com ]             N
is_valid_domain_name? [google-.com]             N
is_valid_domain_name? [.google.com]             N
is_valid_domain_name? [<script]                 N
is_valid_domain_name? [alert(]                  N
is_valid_domain_name? [.]                       N
is_valid_domain_name? [..]                      N
is_valid_domain_name? [ ]                       N
is_valid_domain_name? [-]                       N
is_valid_domain_name? []                        N
user_4610960

If you can run shell commands, following is the best way to determine if a domain is registered.

This function returns false, if domain name isn't registered else returns domain name.

function get_domain_name($domain) { 
    //Step 1 - Return false if any shell sensitive chars or space/tab were found
    if(escapeshellcmd($domain)!=$domain || count(explode(".", $domain))<2 || preg_match("/[\s\t]/", $domain)) {
            return false;
    }

    //Step 2 - Get the root domain in-case of subdomain
    $domain = (count(explode(".", $domain))>2 ? strtolower(explode(".", $domain)[count(explode(".", $domain))-2].".".explode(".", $domain)[count(explode(".", $domain))-1]) : strtolower($domain));

    //Step 3 - Run shell command 'dig' to get SOA servers for the domain extension
    $ns = shell_exec(escapeshellcmd("dig +short SOA ".escapeshellarg(explode(".", $domain)[count(explode(".", $domain))-1]))); 

    //Step 4 - Return false if invalid extension (returns NULL), or take the first server address out of output
    if($ns===NULL) {
            return false;
    }
    $ns = (((preg_split('/\s+/', $ns)[0])[strlen(preg_split('/\s+/', $ns)[0])-1]==".") ? substr(preg_split('/\s+/', $ns)[0], 0, strlen(preg_split('/\s+/', $ns)[0])-1) : preg_split('/\s+/', $ns)[0]);

    //Step 5 - Run another dig using the obtained address for our domain, and return false if returned NULL else return the domain name. This assumes an authoritative NS is assigned when a domain is registered, can be improved to filter more accurately.
    $ans = shell_exec(escapeshellcmd("dig +noall +authority ".escapeshellarg("@".$ns)." ".escapeshellarg($domain))); 
    return (($ans===NULL) ? false : ((strpos($ans, $ns)>-1) ? false : $domain));
}

Pros

  1. Works on any domain, while php dns functions may fail on some domains. (my .pro domain failed on php dns)
  2. Works on fresh domains without any dns (like A) records
  3. Unicode friendly

Cons

  1. Usage of shell execution, probably
user_60606020 
<?php

if(is_valid_domain('https://www.google.com')==1){
  echo 'Valid';
}else{
   echo 'InValid';
}

 function is_valid_domain($url){

    $validation = FALSE;
    /*Parse URL*/    
    $urlparts = parse_url(filter_var($url, FILTER_SANITIZE_URL));

    /*Check host exist else path assign to host*/    
    if(!isset($urlparts['host'])){
        $urlparts['host'] = $urlparts['path'];
    }

    if($urlparts['host']!=''){
        /*Add scheme if not found*/        if (!isset($urlparts['scheme'])){
        $urlparts['scheme'] = 'http';
        }

        /*Validation*/        
    if(checkdnsrr($urlparts['host'], 'A') && in_array($urlparts['scheme'],array('http','https')) && ip2long($urlparts['host']) === FALSE){ 
        $urlparts['host'] = preg_replace('/^www\./', '', $urlparts['host']);
        $url = $urlparts['scheme'].'://'.$urlparts['host']. "/";            

            if (filter_var($url, FILTER_VALIDATE_URL) !== false && @get_headers($url)) {
                $validation = TRUE;
            }
        }
    }

    return $validation;

}
?>
user_105799380

After reading all the issues with the added functions I decided I need something more accurate. Here's what I came up with that works for me.

If you need to specifically validate hostnames (they must start and end with an alphanumberic character and contain only alphanumerics and hyphens) this function should be enough.

function is_valid_domain($domain) {
    // Check for starting and ending hyphen(s)
    if(preg_match('/-./', $domain) || substr($domain, 1) == '-') {
        return false;
    }

    // Detect and convert international UTF-8 domain names to IDNA ASCII form
    if(mb_detect_encoding($domain) != "ASCII") {
        $idn_dom = idn_to_ascii($domain);
    } else {
        $idn_dom = $domain;
    }

    // Validate
    if(filter_var($idn_dom, FILTER_VALIDATE_DOMAIN, FILTER_FLAG_HOSTNAME) != false) {
        return true;
    }
    return false;
}

Note that this function will work on most (haven't tested all languages) LTR languages. It will not work on RTL languages.

is_valid_domain('a');                                                                       Y
is_valid_domain('a.b');                                                                     Y
is_valid_domain('localhost');                                                               Y
is_valid_domain('google.com');                                                              Y
is_valid_domain('news.google.co.uk');                                                       Y
is_valid_domain('xn--fsqu00a.xn--0zwm56d');                                                 Y
is_valid_domain('area51.com');                                                              Y
is_valid_domain('japanese.コム');                                                           Y
is_valid_domain('домейн.бг');                                                               Y
is_valid_domain('goo gle.com');                                                             N
is_valid_domain('google..com');                                                             N
is_valid_domain('google-.com');                                                             N
is_valid_domain('.google.com');                                                             N
is_valid_domain('<script');                                                                 N
is_valid_domain('alert(');                                                                  N
is_valid_domain('.');                                                                       N
is_valid_domain('..');                                                                      N
is_valid_domain(' ');                                                                       N
is_valid_domain('-');                                                                       N
is_valid_domain('');                                                                        N
is_valid_domain('-günter-.de');                                                             N
is_valid_domain('-günter.de');                                                              N
is_valid_domain('günter-.de');                                                              N
is_valid_domain('sadyasgduysgduysdgyuasdgusydgsyudgsuydgusydgsyudgsuydusdsdsdsaad.com');    N
is_valid_domain('2001:db8::7');                                                             N
is_valid_domain('876-555-4321');                                                            N
is_valid_domain('1-876-555-4321');                                                          N
user_15490920
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