


Why Can\'t I Validate Domains in PHP Without Regular Expressions?
Oct 31, 2024 am 05:01 AMPHP domain name verification
Question: How to verify domain name in PHP without using regular expressions?
Verification requirements:
- Starts with a letter or number
- Can contain letters, numbers and hyphens
- Starts with Ending with a letter or number
- Length between 1 and 253 characters
- Each label length between 1 and 63 characters
Possible answers:
Domain name validation without using regular expressions is not possible as multiple rules and restrictions need to be checked.
Regular expression pattern:
/^[a-z\d](-*[a-z\d])*)(\.([a-z\d](-*[a-z\d])*))*$/i
Meaning:
- ^ and $ anchor strings the beginning and end of.
- [a-zd] matches letters or numbers.
- (-*[a-zd])* matches zero or more letters or numbers separated by hyphens.
- . Matches a period.
- {} specifies the number of repetitions.
Sample code:
<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", $domain_name) //valid chars check && preg_match("/^.{1,253}$/", $domain_name) //overall length check && preg_match("/^[^\.]{1,63}(\.[^\.]{1,63})*$/", $domain_name) ); //length of each label }</code>
Test case:
域名 | 有效性 |
---|---|
a | Y |
0 | Y |
a.b | Y |
localhost | Y |
google.com | Y |
news.google.co.uk | Y |
xn--fsqu00a.xn--0zwm56d | Y |
goo gle.com | N |
google..com | N |
google.com | N |
google-.com | N |
.google.com | N |
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