Can Domain Names Be Validated in PHP Without Regular Expressions?

Validating Domain Names in PHP

Can Validation Be Done Without Regular Expressions?

Validating domain names without regular expressions is not recommended due to potential security vulnerabilities and inconsistent results. Regular expressions provide a robust and standardized approach to ensure accuracy.

Regex Pattern for Domain Name Validation

To validate domain names using regular expressions, consider the following pattern:

^([a-z\d](-*[a-z\d])*)(\.([a-z\d](-*[a-z\d])*))*$/i

This expression comprises multiple criteria:

• Valid Characters: Ensures domain names contain only alphanumeric characters, hyphens, and periods.
• Overall Length: Domain names must not exceed 253 characters in length.
• Individual Label Length: Each label (the part separated by periods) must not exceed 63 characters.

Custom Validation Function

An improved PHP function for domain name validation:

<code class="php">function is_valid_domain_name($domain_name)
{
    return (preg_match("/^([a-z\d](-*[a-z\d])*)(\.([a-z\d](-*[a-z\d])*))*$/i", $domain_name)
            &amp;&amp; preg_match("/^.{1,253}$/", $domain_name)
            &amp;&amp; preg_match("/^[^\.]{1,63}(\.[^\.]{1,63})*$/", $domain_name));
}</code>

Test Cases

Domain Name	Validation Result
a	Yes
0	Yes
a.b	Yes
localhost	Yes
google.com	Yes
news.google.co.uk	Yes
xn--fsqu00a.xn--0zwm56d	Yes
goo gle.com	No
google..com	No
google.com	No
google-.com	No
.google.com	No
	No
alert(	No
.	No
..	No
	No
-	No
	No

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