$str = "[test]";
$str = ltrim($str,1); //becomes test]
$str = rtrim($str,1); //becomes test

function my_rtrim($str, $count) {
  return substr($str, 0, -$count);
}

function my_ltrim($str, $count) {
  return substr($str, $count);
}

substr("abcdef", 0, -1);     // 'abcde'
substr("abcdef", 1);         // 'bcdef'

substr('abcdef', 1, -1)