How to Validate Password using Regular Expressions in PHP ?

Password validation is a crucial part of web application security. Regular expressions provide a powerful tool to define complex patterns. This article will guide you through various approaches to validate passwords using regular expressions in PHP.

Approach 1: Basic Password Validation

In this case, we will use basic password validation using a regular expression.

The basic password contains -

• password minimum length should be 8.
• at least one uppercase letter,
• at least one lowercase letter,
• and one digit.

<?php

$password = "GeeksforGeeks@123";

$pattern = '/^(?=.*[a-z])(?=.*[A-Z])(?=.*\d).{8,}$/';

if (preg_match($pattern, $password)) {
    echo "Valid Password";
} else {
    echo "Invalid Password";
}

?>

Valid Password

In the above example -

• (?=.*[a-z]): At least one lowercase letter.
• (?=.*[A-Z]): At least one uppercase letter.
• (?=.*\d): At least one digit.
• .{8,}: Minimum length of 8 characters.

Approach 2: Enhanced Password Strength

In this case, we will check the password contains -

• minimum length should be 8.
• at least one uppercase letter.
• at least one lowercase letter.
• at least one digits, and
• at least one special character.

<?php

$password = "GeeksforGeeks@123";

$pattern = '/^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)(?=.*[\W_]).{8,}$/';

if (preg_match($pattern, $password)) {
    echo "Valid Password";
} else {
    echo "Invalid Password";
}

?>

Valid Password

In above example, (?=.*[\W_]) defines at least one special character.