code: public function getString($type = 'letter', $desired_length = null)
  	{
  		if (empty($desired_length)) {
  			$desired_length = $this->getInteger(1, 50);
  		}
  		
  		$result = '';
  		
  		while (strlen($result) < $desired_length) {
  			if ($type == 'letter') {
  				$result .= $this->getLetter();
  			} elseif ($type == 'number') {
  				$result .= $this->getInteger(1, 10);
  			} else {
  				// Mix letters/numbers.
  				$result .= $this->getUniqueHash();
  			}
  		}
  		
  		return substr($result, 0, $desired_length);
  	}
docs: Generate random string.
  
  @access public
  @param string $type Options: letter, number, or mix.	 default: letter
  @param mixed $desired_length Will be random length if not specified.
  @return string