Regular Expression

[wuno]

Hello

I need to check if the usser id contains valid string characters. There are some rules that apply to the user id input validation.

1. The first character of the user id has to be lower case of english letters.

2. The user id has to be in lower case.

3. The user id can only contain numbers, english letters and underscore(_).

4. The last character of the user id can't be underscore(_).

5. The underscore(_) can't appear continuously, for example __

I need regular expression to perform the check of the valid user id.

Thanks.

Norman

[Weedpacket]

Right; and how far have you got so far? (I recommend not trying to do all this in one regular expression. For example, part 5 can be done as strpos('__',$user)===false, part 4 as $user[strlen($user)-1]!='_', and part 3 as preg_match('/^{[a-z0-9]$/i',} $user)).