https://blog.gongquiz.com/2023/02/28/%ec%9c%a0%eb%8b%89%ec%8a%a4unix-%eb%aa%85%eb%a0%b9%ec%96%b4-%ec%a4%91-dos%ec%9d%98-dir%ea%b3%bc-%ea%b0%99%ec%9d%80-%ec%97%ad%ed%95%a0%ec%9d%84-%ed%95%98%eb%8a%94-%eb%aa%85%eb%a0%b9%ec%9d%80/