为什么我的电子邮件验证不起作用？ PHP

I have used

if (!preg_match('/[a-z||0-9]@[a-z||0-9].[a-z]/', $email)) {
    [PRINT ERROR]
}

&

if (!eregi( "^[0-9]+$", $email)) {
    [PRINT ERROR]
}

&

if (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
    [PRINT ERROR]
}

I have also tried taking out the ! and make it work backwards but for some reason NONE of those work to find out if it is valid. Any ideas why?... I have it in an else if statement, Im not sure if that could be the cause..

I am using PHP

Try

'/[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,4}/'

...

if (!preg_match('/[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,4}/', strtoupper($email))) {
    [PRINT ERROR]
}

As far as I can see, none of your regex expressions would match an email.

Check your php version. eregi is deprecated after 5.3.0. Also, the regex is not correct.

Try this from the Kohana source code:

function email($email)
{
    return (bool) preg_match('/^[-_a-z0-9\'+*$^&%=~!?{}]++(?:\.[-_a-z0-9\'+*$^&%=~!?{}]+)*+@(?:(?![-.])[-a-z0-9.]+(?<![-.])\.[a-z]{2,6}|\d{1,3}(?:\.\d{1,3}){3})(?::\d++)?$/iD', (string) $email);
}

Try this (from wordpress):

// from wordpress code: wp-includes/formatting.php
function is_email($user_email)
{
    $chars = "/^([a-z0-9+_]|\\-|\\.)+@(([a-z0-9_]|\\-)+\\.)+[a-z]{2,6}\$/i";

    if (strpos($user_email, '@') !== false && strpos($user_email, '.') !== false)
    {
        if (preg_match($chars, $user_email)) {
            return true;
        } else {
            return false;
        }
    } else {
        return false;
    }
}