public function wd($dir = null, $code = E_USER_WARNING){
		if(null !== $dir && is_dir($dir)){
			$this->wd = $dir;
			if(chdir($dir) === false){
			    throw new \Exception('Cannot change to directory '.$dir.' in '.__METHOD__, $code);
				return $this;
			}
		}else{
			$dir = $this->wd;
		}
		return $this;
	}