How Do I Make A Username Require _ In A Form

[system]

Hello. I have a php, mysql and jquery login and registration sliding system, all works fine but if this requires a new user to use between 4 and 32 characters:

[php]if(preg_match(’/[^a-z0-9-_.]+/i’,$_POST[‘username’]))
{
$err[]=‘Your username contains invalid characters!’;
}[/php]

How do I make it so the use HAS to have a name example of: John_Doe (with the underscore in the middle of the name) both parts of the name having to be 4 or more characters.

I think I’ve fixed the 4 or more character part by changing the above code to 9 or more (John_Test), like this or more.

I will appreciate your help very much, I am making a San Andreas Multiplayer roleplaying community and need the registration system set up correctly.

[richei]

That’s not going to check the length of the string, all it does is check the characters. to do that, you’d need to use strlen().
[php]if(strlen($_POST[‘username’]) > 4 && strlen($_POST[‘usernae’]) < 32) {
if(!preg_match(’/[^a-z0-9-_.]+/i’,$_POST[‘username’])) {
$err[] = ‘Your username contains invalid characters!’;
}
} else {
$err[] = “Username must be between 4 and 32 characters”;
}[/php]

[Aphex]

Please close this post because I have now registered my username and it won’t let me edit it. I have made a new one, I posted the wrong part of my script in this one. Thanks!