http://tetzzang.com/%ec%95%88%eb%93%9c%eb%a1%9c%ec%9d%b4%eb%93%9c-shell%ec%97%90%ec%84%9c-%ec%84%a4%ec%b9%98%eb%90%9c-%ec%95%b1%ec%9d%98-%ec%a0%95%eb%b3%b4-%ed%99%95%ec%9d%b8%ed%95%98%eb%8a%94-%eb%b0%a9%eb%b2%95/