Given a string e.g. “domain.com” we want to find out if it is a valid domain string name. We can do this in PHP via Regx aka Regular Expression. We can perform 3 checks: first, the characters need to be lowercase/uppercases, digits, hypens, and dots. Second, the overall domain length should between 1 to 253. Lastly, the length of each label (separated by dots) should be no longer than 63 characters.
The following is a handy PHP function can validate the domain string:
1 2 3 4 5 6 7 8 | <?php if (!function_exists("is_valid_domain_name")) { function is_valid_domain_name($domain_name) { return (preg_match("/^([a-z\d](-*[a-z\d])*)(\.([a-z\d](-*[a-z\d])*))*$/i", $domain_name) //valid chars check && preg_match("/^.{1,253}$/", $domain_name) //overall length check && preg_match("/^[^\.]{1,63}(\.[^\.]{1,63})*$/", $domain_name) ); //length of each label } } |
<?php
if (!function_exists("is_valid_domain_name")) {
function is_valid_domain_name($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
}
}For example:
1 2 | is_valid_domain_name("domain.com"); // true is_valid_domain_name("--anothers"); // false |
is_valid_domain_name("domain.com"); // true
is_valid_domain_name("--anothers"); // false–EOF (The Ultimate Computing & Technology Blog) —
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