cal
cal 用于查看日历等时间信息，如只有一个参数，则表示年份(1-9999)，如有两个参数，则表示月份和年份
语法:
cal [general options] [-jy] [[month] year]
cal [general options] [-j] [-m month] [year]
ncal -C [general options] [-jy] [[month] year]
ncal -C [general options] [-j] [-m month] [year]
ncal [general options] [-bhJjpwySM] [-H yyyy-mm-dd] [-s country_code] [[month] year]
ncal [general options] [-bhJeoSM] [year]
选项:
-y 显示一年
-j 按天数显示
操作: