正则表达式匹配user @ domain：port

Question

I have to match a string as user@domain:port. So it should allow domain or domain:port or user@domain or user@domain:port complete. Initially i had written multiple regular expressions to match some of these conditions as following:

preg_match('/^[A-z0-9_\-]+[@][A-z0-9_\-]+([.][A-z0-9_\-]+)+[A-z.]{2,4}$/', $str) or preg_match('/^[A-z0-9_\-]+([.][A-z0-9_\-]+)+[A-z.]{2,4}$/', $str) or preg_match('/^[A-z0-9_\-]+([.][A-z0-9_\-]+)+[A-z.]{2,4}+([:][0-9]+)$/', $str)

but now i have to cover all conditions as above and i think there should be a single expression which will pass all conditions.

Can someone please tell me the correct regular exp to match all conditions with some explanation?

I want to do it in PHP.

Answer 1

Here is something to help you

The regex

^(?:([\w-]+)@)?([\w-\.]+\.[a-zA-Z][\w-]+)(?::([0-9]{1,5}))?$

Should do what you want. Let's explain : You first want to match (if it exist) a user followed by @. To match a word you can use \w but in your regex you specified that you wanted the char - wich isn't include in \w (but _ is). So to match your user you will do :

(?:([\w-]*)@)?

Then you want to match a domain name

([\w-\.]+\.[a-zA-Z][\w-]+)

The domain name have to finish by at least one dot followed by a word (the top level domain). The top level domain doesn't begin by a digit (this rule was created based on the usedTopLevelDomainList

And to finish you want to match a port wich is a 1-5 digit :

(?::([0-9]{0,5}))?

---

As pointed out the regex can match IPv4 that aren't within the 255 max range. The regex to verify an IPv4 is :

^(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$

Source. I've updated the previous regex to exclude the IP match from my regex and add a OR statement for the domain name to match either an IPv4 based on the above regex or a domain as I've defined it previously.

Result with group to separate each part :

^(?:([\w-]+)@)?((?:[\w-\.]+\.[a-zA-Z][\w-]+)|(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?))(?::([0-9]{1,5}))?$

Result without any group to just match valid case :

^(?:[\w-]+@)?(?:(?:[\w-\.]+\.[a-zA-Z][\w-]+)|(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?))(?::[0-9]{1,5})?$