在linux下獲取時間字符串
命令 date
# 以yyyymmdd格式輸出23天之前現在這個時刻的時間
$ date +%Y%m%d –date=’23 days ago’

$ date -u
Thu Sep 28 09:32:04 UTC 2006

$ date -R
Thu, 28 Sep 2006 17:32:28 +0800

# 測試十億分之一秒
$ date +’%Y%m%d %H:%M:%S.%N’;date +’%Y%m%d %H:%M:%S.%N’;date +’%Y%m%d %H:%M:%S.%N’;date +’%Y%m%d %H:%M:%S.%N’
20060928 17:44:20.906805000
20060928 17:44:20.909188000
20060928 17:44:20.911535000
20060928 17:44:20.913886000
date 參考
$ date –help
Usage: date [OPTION]… [+FORMAT]
or: date [-u|--utc|--universal] [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’
# such as ‘n days ago |1 month ago|n years ago’
-f, –file=DATEFILE like –date once for each line of DATEFILE
-ITIMESPEC, –iso-8601[=TIMESPEC] output date/time in ISO 8601 format.
TIMESPEC=`date’ for date only,
`hours’, `minutes’, or `seconds’ for date and
time to the indicated precision.
–iso-8601 without TIMESPEC defaults to `date’.
-r, –reference=FILE display the last modification time of FILE
-R, –rfc-2822 output RFC-2822 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

FORMAT controls the output. The only valid option for the second form
specifies Coordinated Universal Time. Interpreted sequences are:

%% 輸出%符號 a literal %
%a 當前域的星期縮寫 locale’s abbreviated weekday name (Sun..Sat)
%A 當前域的星期全寫 locale’s full weekday name, variable length (Sunday..Saturday)
%b 當前域的月份縮寫 locale’s abbreviated month name (Jan..Dec)
%B 當前域的月份全稱 locale’s full month name, variable length (January..December)
%c 當前域的默認時間格式 locale’s date and time (Sat Nov 04 12:02:33 EST 1989)
%C n百年 century (year divided by 100 and truncated to an integer) [00-99]
%d 兩位的天 day of month (01..31)
%D 短時間格式 date (mm/dd/yy)
%e 短格式天 day of month, blank padded ( 1..31)
%F 文件時間格式 same as %Y-%m-%d
%g the 2-digit year corresponding to the %V week number
%G the 4-digit year corresponding to the %V week number
%h same as %b
%H 24小時制的小時 hour (00..23)
%I 12小時制的小時 hour (01..12)
%j 一年中的第幾天 day of year (001..366)
%k 短格式24小時制的小時 hour ( 0..23)
%l 短格式12小時制的小時 hour ( 1..12)
%m 雙位月份 month (01..12)
%M 雙位分鐘 minute (00..59)
%n 換行 a newline
%N 十億分之一秒 nanoseconds (000000000..999999999)
%p 大寫的當前域的上下午指示 locale’s upper case AM or PM indicator (blank in many locales)
%P 小寫的當前域的上下午指示 locale’s lower case am or pm indicator (blank in many locales)
%r 12小時制的時間表示（時:分:秒,雙位） time, 12-hour (hh:mm:ss [AP]M)
%R 24小時制的時間表示 （時:分,雙位）time, 24-hour (hh:mm)
%s 自基礎時間 1970-01-01 00:00:00 到當前時刻的秒數 seconds since `00:00:00 1970-01-01 UTC’ (a GNU extension)
%S 雙位秒 second (00..60); the 60 is necessary to accommodate a leap second
%t 橫向制表位(tab) a horizontal tab
%T 24小時制時間表示 time, 24-hour (hh:mm:ss)
%u 數字表示的星期（從星期一開始 1-7）day of week (1..7); 1 represents Monday
%U 一年中的第幾周星期天為開始 week number of year with Sunday as first day of week (00..53)
%V 一年中的第幾周星期一為開始 week number of year with Monday as first day of week (01..53)
%w 一周中的第幾天 星期天為開始 0-6 day of week (0..6); 0 represents Sunday
%W 一年中的第幾周星期一為開始 week number of year with Monday as first day of week (00..53)
%x 本地日期格式 locale’s date representation (mm/dd/yy)
%X 本地時間格式 locale’s time representation (%H:%M:%S)
%y 兩位的年 last two digits of year (00..99)
%Y 年 year (1970…)
%z RFC-2822 標準時間格式表示的域 RFC-2822 style numeric timezone (-0500) (a nonstandard extension)
%Z 時間域 time zone (e.g., EDT), or nothing if no time zone is determinable

By default, date pads numeric fields with zeroes. GNU date recognizes
the following modifiers between `%’ and a numeric directive.

`-’ (hyphen) do not pad the field
`_’ (underscore) pad the field with spaces