How to change PHP's eregi to preg_match

Question

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How can I convert ereg expressions to preg in PHP?

I need help, below is a small VERY basic regex to somewhat validate an email, I do realize it does not work the greatest but for my needs it is ok for now.

It currently uses PHP's eregi function which php.net says is now a depreciated function and I should use preg_match instead, simply replacing erei with preg_match does not work, can someone show me how to make it work?

function validate_email($email) {
    if (!eregi("^[[:alnum:]][a-z0-9_.-]*@[a-z0-9.-]+\.[a-z]{2,4}$", $email)) {
        echo 'bad email';
    } else {
        echo 'good email';
    }
}
function validate_email($email) {
    if (!preg_match("^[[:alnum:]][a-z0-9_.-]*@[a-z0-9.-]+\.[a-z]{2,4}$", $email)) {
        echo 'bad email';
    } else {
        echo 'good email';
    }
}

Answer 1

Perl-style regex patterns always need to be delimited. The very first character in the string is considered the delimiter, so something like this:

function validate_email($email) {
    if (!preg_match("/^[[:alnum:]][a-z0-9_.-]*@[a-z0-9.-]+\.[a-z]{2,4}$/i", $email)) {
        echo 'bad email';
    } else {
        echo 'good email';
    }
}

The reason your initial attempt didn't work is because it was trying to use ^ as the delimiter character but (obviously) found no matching ^ for the end of the regex.