Linux date command details

Name: Date
Permission: All Users
Usage: date [-u] [-D datestr] [-s datestr] [-- UTC] [-- Universal] [-- date = datestr] [-- set = datestr] [-- help] [-- version] [+ format] [mmddhhmm [[CC] YY] [. SS]
Note: date can be used to display or set the date and time of the system. In terms of display, users can set the format to be displayed. The format is set to a plus sign followed by several tags, the available tags are listed as follows:
Time:
%: Printed
% N: Next row
% T: Skip
% H: hour (00 .. 23)
% I: hour (01 .. 12)
% K: hour (0 .. 23)
% L: hour (1 .. 12)
% M: minute (00 .. 59)
% P: displays local am or PM
% R: direct display time (in 12-hour format: hh: mm: ss [AP] m)
% S: number of seconds from January 1, 1970 00:00:00 UTC till now % s: seconds (00 .. 61)
% T: direct display time (in 24-hour format)
% X: equivalent to % H: % m: % s
% Z: display the time zone
Date:
% A: The day of the week (Sun .. SAT)
% A: The day of the week (Sunday .. Saturday)
% B: Month (Jan .. dec)
% B: Month (January... December)
% C: Display date and time directly
% D: Day (01 .. 31)
% D: Display date directly (mm/DD/yy)
% H: Same as % B
% J: The day of the year (001 .. 366)
% M: Month (01 .. 12)
% U: Week (00 .. 53) of the year (the first day of the week on Sunday)
% W: The day of the week (0 .. 6)
% W: Week (00 .. 53) of the Year (Monday is the first day of the week)
% X: Display date directly (mm/DD/yy)
% Y: last two digits of the Year (00.99)
% Y: full year (0000 .. 9999)
If it does not start with a plus sign, the time is set, and the time format is mmddhhmm [[CC] YY] [. SS].
MM indicates the month,
Dd is a day,
HH is the hour,
Mm is minute,
CC is the first two digits of the year,
YY is the last two digits of the year,
SS is the number of seconds
Calculation:
-D datestr: display the time set in datestr (non-system time)
-- Help: displays auxiliary messages.
-S datestr: set the system time to the time set in datestr
-U: displays the current Greenwich Mean Time.
-- Version: displays the version number.
Example:
The current date is displayed: date + % T % N % d
Show month and day: date + % B % d
Display date and set time (12:34:56): date -- date 12:34:56
Set the current system time (12:34:56): date -- s 12:34:56
Note: If you do not want meaningless 0 values (for example,), you can insert the-symbol in the tag, for example, date + %-H: %-M: %-s removes the meaningless 0 in the hour, minute, and second, as if the original 08:09:04 will change. In addition, you can set the system time only when you have the permission (such as root. After you change the system time as root, remember to write the system time to CMOS using clock-w, in this way, the system time will continue to hold the latest correct value upon the next reboot.
NTP Time Synchronization
The NTP service is installed by default in Linux. Manual NTP synchronization is as follows:
Ntpdate ntp1.nl.net
Of course, other NTP servers can also be specified.

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Extended Functions

The date tool can do more work, not just print out the current system date. You can use it to obtain the day of the week for the given date, and obtain the relative date relative to the current date. Know the day of a week

Another extension of GNU's date command is the-D option. This option is useful when there is no calendar table on your table (Unix users do not need a calendar table. With this powerful option, you can quickly find out the day of the week for a specific date by enclose the date as a parameter enclosed by quotation marks:

$ Date-d "Nov 22"
Wed Nov 22 00:00:00 est 2006
$

In this example, you can see that July 22, November 22 is Wednesday this year.

Therefore, if you hold a major meeting on July 15, November 22, you can immediately learn that this day is Wednesday and that day you will arrive at the resident office.

Get relative date

The D option also tells you which day is relative to the current date, from the current several days or after several weeks, or before (past ). You can complete this task by enclose the relative offset in quotation marks as a parameter of the-D option.

For example, you need to know the date two weeks later. If you are at the shell prompt, you can quickly get the answer:

$ Date-D '2 weeks'

There are other important methods to use this command. With the next/last command, you can get the day of the week in the future:

$ Date-D 'Next Monday' (next Monday)

$ Date-D next-day + % Y % m % d (tomorrow's date) or: Date-d tomorrow + % Y % m % d

$ Date-d last-Day + % Y % m % d (date of yesterday) or: Date-d Yesterday + % Y % m % d

$ Date-d last-month + % Y % m (last month)

$ Date-D next-month + % Y % m (What month is next)

Using the AGO command, you can get the past date:

$ Date-D '30 days ago '(date 30 days ago)

You can use a negative number to get the opposite Date:

$ Date-D 'dec 14-2 weeks '(relative: date two weeks before Dec 14)
$ Date-d '-100 days' (date before 100 days)
$ Date-D '50 days '(date after 50 days)

This technique is very useful. It can Set reminders for itself based on future dates, possibly in scripts or shell startup files, as shown below:

Day = 'date-d' 2 weeks '+ "% B % d "'
If test "'echo $ Day'" = "Aug 16"; Then ECHO 'product launch is now two weeks away! '; FI