How to create a regular expression to validate an internet domain? The rules are below:
Remember that the validation in question refers between the beginning of the value and the first point. Example: domain .com.br.
It will be used for both URLs and emails.
Here is the code I did:
([^-](([a-zA-Z0-9]?)*([a-zA-Z-])([a-zA-Z0-9]?))+[^-])\.
The closest I got to the answer, the hyphens need to be removed at the beginning and end:
((([\w]?)+([a-zA-Z-_])([\w]?)+){2,26})\.
What about:
^(?!\d+\.)(\w[\w\-]{0,24}\w)\.
(?!\d+\.) is a negative lookahead. He checks that the domain is not just digits.
\w after the first character is consistently a [\w\-]{0,24} , there may be 0 or 24 letters, numbers, or hyphen.
não hífen The last character can not also be a hyphen.
\w start of the rest of the domain you are not interested in.
In \. you expect (\w[\w\-]{0,24}\w) + 1 caracter não hífen + 0 até 24 letras, números ou hífen . These three rules together guarantee that your domain will be at least 2 characters and a maximum of 26 characters.
You can see the regex running here .
Notes:
The above regex does not handle letters in other languages, as commented out by @Bacoo, because ECMAScript 5 and below do not provide native support for Unicode regexes ( ECMAScript 6 sim ).
The same regex could be implemented in PHP (which supports Unicode regexes) as follows:
^(?!\d+\.)([\p{L}0-9][\p{L}0-9\-]{0,24}[\p{L}0-9])\.
where 1 caracter não hífen replaces [\p{L}0-9] to accept any letters in any languages + digits. You can see this regex running here .