I'm currently writing a register script (where users register for an account on my site).

I want to check the username, password and email.

only letters [both upper and lower] and underscores (_) are allowed for the username no spaces are allowed

only letters [both upper and lower] and numbers allowed for the password and again no spaces are allowed.

and i want to check if the email is a proper email address, so the user cant submit something like aslfdjhgk for the email

The only real, guaranteed way to verify the email address is to do a 2-step registration. You'd have to send a confirmation email to the email address specified by the user, and then have them click on a link in the email to verify the registration.

You can do "simple" verification on email addresses by making sure they're [some characters][@][more characters][.][more characters], but that would allow asfdjsd@asfdsdf.com, for example.

The 2 step appraoch is by far the most sucessfull.

You can fiddle with the getmxrr method or the try connecting to the mail server with a socket but even with these two methods it sometimes failes on valid emails.

So I send them a confirmation email with an activation link.

No activation within a month they get an email, still no activation then drop that row.

Ibbo

thanks

what about validating the username and password submitted, im a bit of a n00b to php so i dont know what code to use.

regular expressions? dont know how to use them

also how could i automatically get php to remove the user if the email isnt validated after a certain period of time?

Well for the username I stick to this rule.

A it must be over 6 chars long, B it must not start with any numbers or non alpha chars.

so if(strlen($user) < 6) || preg_match('/^[0-9][!|"|£|$|%|^|&|*|(|)|_|-/', $user)) { fail }

Same applies to the password though I let them use anything in a pass so long as it is over 6 chars long.

When your user register they get a registration date with there details. As you go through adding users/ polling for results you can add that xtra overhead by checking for out of date accounts. if say its over a month since registering and they have not activated then drop that row.

Of course you need to be a bit smarter and first of all send out a last chance email.

If then they dont respond to that then drop it.

Ibbo