用法: date [OPTION]... [+FORMAT]
或: date [OPTION] [MMDDhhmm[[CC]YY][.ss]]
Display the current time in the given FORMAT, or set the system date.
-d, --date=STRING display time described by STRING, not `now'
-f, --file=DATEFILE like --date once for each line of DATEFILE
-I, --iso-8601[=TIMESPEC] output an ISO-8601 compliant date/time string.
TIMESPEC=`date' (or missing) for date only,
`hours', `minutes', or `seconds' for date and
time to the indicated precision.
-r, --reference=FILE display the last modification time of FILE
-R, --rfc-822 output RFC-822 compliant date string
-s, --set=STRING set time described by STRING
-u, --utc, --universal print or set Coordinated Universal Time
--help display this help and exit
--version output version information and exit