Username may contain lowercase characters and numbers

Question

I want to allow lowercase characters and numbers in username field.

But with following conditions...

• Only numbers as username NOT allowed (e.g. only mobile number)
• Only lowercase characters allowed (e.g. without any number in username)
• Lowercase characters + numbers allowed (e.g. combination of lowercase and numbers)
• Minimum length 8 characters required
• Maximum length 20 characters allowed

What php regex will do it ?

I tried with following, but it forces lowercase + numbers. Only lowercase username not allowing.

$username_pattern = '/^(?=.*[a-z])(?=.*[a-z])(?=.*\d)[a-z0-9]{8,20}$/';

I want only lowercase and/or lowercase+numbers ( min 8 and max 20 ) in username

Help appreciated.

Answer 1

You can simplify it to not allowing only digits

^(?!\d*$)[a-z0-9]{8,20}$

Explanation

• ^ Start of string
• (?!\d*$) Negative lookahead, assert not only digits till end of string
• [a-z0-9]{8,20} Match 8-20 times a char a-z or a digit 0-9
• $ End of string

Regex demo | Php demo

$username_pattern = '/^(?!\d*$)[a-z0-9]{8,20}$/';
$userNames = [
    "1a3b5678",
    "1a3b5678abcd",
    "12345678",
    "1a3b5678abcddddddddddddddddddddddddddddddd",
    "1a3B5678",
    "a1"
];

foreach ($userNames as $userName) {
    if (preg_match($username_pattern, $userName)) {
        echo "Match - $userName" . PHP_EOL;
    } else {
        echo "No match - $userName" . PHP_EOL;
    }
}

Output

Match - 1a3b5678
Match - 1a3b5678abcd
No match - 12345678
No match - 1a3b5678abcddddddddddddddddddddddddddddddd
No match - 1a3B5678
No match - a1