PHP/パスワード生成

vY4xI6Wf
PHP
if(isset($_POST["pass"])){
		$num = $_POST["pass"];
	} else {
		$num = 3;
	}
	$az = range('a', 'z');
	$AZ = range('A', 'Z');
	$zq = range(0, 9);
	$arr = array_merge($az, $AZ, $zq);
	shuffle($arr);
	echo substr(implode($arr), 0, $num);