Question

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regular expression for letters, numbers and – _

I am creating a signup form in PHP and need to ensure that user’s usernames don’t contain unwanted characters. Is there anyway I can create a function that returns true for A-Z a-z 0-9 - . _.

Also I do not want the user’s emails to be from yahoo as for some reason they reject the confirmation emails sent. Along with __FILTER_VALIDATE_EMAIL__what would I need to add?

PS: is there anything wrong with the characters I have mentioned above? I have noted that gmail doesn’t allow -_ only . and YouTube only alpha-numeric characters.

Answer 1

Edited to use \w instead of a-zA-Z0-9_

if(preg_match("/[^\w-.]/", $user)){
    // invalid character
}
if(!filter_var($email, FILTER_VALIDATE_EMAIL) || strstr($email,'@yahoo.com')) {
    // either invalid email, or it contains in @yahoo.com
}