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build a regex for password check

Hi i have a password strength check in PHP. that looks like this:

    public static function validPass($candidate) {
    $r1 = '/[A-Z]/';  //1 upper
    $r2 = '/[a-z]/';  //2 lower
    $r3 = '/[!@#$%^&*()\-_=+{}:<.>]/';  //1 special char
    $r4 = '/[0-9]/';  //1 number

    //no space
    if (preg_match('/\s/',$candidate)) {
        return false;
    }

    if (preg_match_all($r1, $candidate, $o) < 1) {
        return false;
    }
    if (preg_match_all($r2, $candidate, $o) < 1) {
        return false;
    }
    if (preg_match_all($r3, $candidate, $o) < 1) {
        return false;
    }
    if (preg_match_all($r4, $candidate, $o) < 1) {
        return false;
    }
    return true;
}

so 1 capital, 1 lower, 1 number, 1 special char and no spaces allowed

now i am using a javascript validator for the frontend and the only custom feature i can add for password is to add a regex so i have to build this into a regex. I tried and I have so far:

^(?=.*[^a-zA-Z])(?=.*[a-z])(?=.*[A-Z])$

but i dont know how to approach this. What is the best way to perform these checks into a regex?

6 months ago · Santiago Trujillo

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Accepted Answer · 2022-05-26T16:46:43.964Z

Your ^(?=.*[^a-zA-Z])(?=.*[a-z])(?=.*[A-Z])$ pattern is an example of a regex that will never match because, with lookaheads, you require at least 1 non-letter, uppercase and lowercase letters, but the consuming pattern only matches an empty string.

You may use a single regex like

^(?=.*[A-Z])(?=.*[a-z])(?=.*[!@#$%^&*()_=+{}:<.>-])(?=.*[0-9])\S*$

If you need to set a minmum number of characters, replace the last * with a limiting quantifier, e.g. {8,} to require at least 8 chars.

See the regex demo.

Details:

^ - start of string
(?=.*[A-Z]) - at least one uppercase
(?=.*[a-z]) - - at least one lowercase
(?=.*[!@#$%^&*()_=+{}:<.>-]) - at least one special char
(?=.*[0-9]) - at least one digit
\S* - 0 or more non-whitespace chars
$ - end of strings.