Valid domain name [duplicate]

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Possible Duplicate:

PHP validation/regex for URL

I'm building a small app in PHP, and have to validate domain names (for use in E-mail addresses). For instance if I have mads@gmail.com I want to check if gmail.com is a valid domain name (I'm essentially throwing away the part before the @).

I have been using the following code:

if (!preg_match ("/^[a-z0-9][a-z0-9\-]+[a-z0-9](\.[a-z]{2,4})+$/i", trim($valid_emails[$i]))) {
         // Return error
}

And everything has been working fine. Until I got GE MoneyBank as a client. They are using ge.com as their domain, and开发者_运维知识库 that doesn't pass.

I have a rudimentary understanding of regex, and have tried deleting some of the [a-z0-9] blocks so the minimum character count comes down to 2, but without luck. Can anyone with more experience point me in the right direction?

Thanks in advance

---

What you currently have does the following:
- [a-z0-9]: A letter or a number
- [a-z0-9\-]+: A letter or a number or a hyphen, 1 or more times
- [a-z0-9]: A letter or a number

Your problem is that it is expecting at least 3 letters.

You need to make sure it can accept only two letters, and the last one can't be a hyphen.

So you need to change the middle expression to 0 or more times:
- [a-z0-9\-]*: A letter or a number or a hyphen, 0 or more times