Check if a string is a valid string

isValidString.php

function isValidString($string)
{
    if (empty($string)) {
        return false;
    }

    if (preg_match("/[\||\'|\<|\>|\[|\]|\"|\!|\?|\$|\@|\/|\\\|\&\~\*\{\+]/", $string)) {
        return false;
    } else {
        return true;
    }
}