Check for password strength, password should be at least n characters, contain at least one number, contain at least one lowercase letter, contain at least one uppercase letter, contain at least one special character.

password_strength.php

<?php

$password_length = 8;

function password_strength($password) {
	$returnVal = True;

	if ( strlen($password) < $password_length ) {
		$returnVal = False;
	}

	if ( !preg_match("#[0-9]+#", $password) ) {
		$returnVal = False;
	}

	if ( !preg_match("#[a-z]+#", $password) ) {
		$returnVal = False;
	}

	if ( !preg_match("#[A-Z]+#", $password) ) {
		$returnVal = False;
	}

	if ( !preg_match("/[\'^£$%&*()}{@#~?><>,|=_+!-]/", $password) ) {
		$returnVal = False;
	}

	return $returnVal;

}
?>