The date command is used to print system time and date. It can also set system time and date, but you should generally use ntp daemon to handle this for you.
When used without options, the date command displays the current system time and date:
$ date
Sun Sep 23 03:55:04 UTC 2018As you can see, the default output includes the day of the week (Sun), the day of the month (Sep 23), time (03:55:04), timezone (UTC), and year (2018).
By default, the date displays information about the current date and time, but you can make it show information about a specific date in the past or the future with the -d option.
For example, to find out what day of the week will be October 26 of this year, I could use one of the following commands:
$ date -d 'October 26'
Fri Oct 26 00:00:00 UTC 2018
$ date -d '2018-10-26'
Fri Oct 26 00:00:00 UTC 2018
$ date -d '10/26/2018'
Fri Oct 26 00:00:00 UTC 2018date also accepts words like day of the week, "today", and "yesterday":
$ date -d yesterday
Sat Sep 22 04:11:12 UTC 2018
$ date -d friday
Fri Sep 28 00:00:00 UTC 2018
$ date -d sun
Sun Sep 23 00:00:00 UTC 2018Notice how for future dates the time is set to be 00:00:00 and for past dates it displays the current system time.
Other valid date strings include: last-week, next-week, last-month, next-month, last-year, and next-year.
date can display given date/time in Unix epoch time format, i.e the number of seconds elapsed since 00:00:00, Jan 1, 1970. For this to work, you need to use %s output format specifier.
The following example will show you the seconds from epoch to the current time:
$ date +%s
1537676319And again, use can use the -d option to count the number of seconds since the epoch to a specific date.
$ date -d '10/26/2018' +%s
1540512000To convert seconds from the epoch to a human readable date, use the -d option and prepend the number of seconds with the @ sign:
$ date -d @1540512000
Fri Oct 26 00:00:00 UTC 2018Note that the command above won't work on Mac OSX, use the following command instead:
$ date -r 1540512000
Thu Oct 25 17:00:00 PDT 2018Notice how it showed a different date because of the timezone difference.
To specify a different timezone other than the system default, set the TZ environment variable when running the date command:
$ date
Sun Sep 23 04:55:20 UTC 2018
$ TZ=Europe/Moscow date
Sun Sep 23 07:55:22 MSK 2018
$ date -d @1540512000
Fri Oct 26 00:00:00 UTC 2018
$ TZ=US/Pacific date -d @1540512000
Thu Oct 25 17:00:00 PDT 2018You can find available timezones by listing /usr/share/zoneinfo directory:
$ ls /usr/share/zoneinfo/
Africa Brazil Egypt GB-Eire HST Japan MST7MDT posix Singapore WET
America Canada Eire GMT Iceland Kwajalein Navajo posixrules Turkey W-SU
Antarctica CET EST GMT0 Indian leapseconds NZ PRC tzdata.zi zone1970.tab
Arctic Chile EST5EDT GMT-0 Iran Libya NZ-CHAT PST8PDT UCT zone.tab
Asia CST6CDT Etc GMT+0 iso3166.tab MET Pacific right Universal Zulu
Atlantic Cuba Europe Greenwich Israel Mexico Poland ROC US
Australia EET GB Hongkong Jamaica MST Portugal ROK UTCThere is also the -u option which makes the date command act as if the TZ environment variable was set to UTC.
$ date -u
Sun Sep 23 05:10:21 UTC 2018You can overwrite the default output of the date command using format specifiers. Examples of format specifiers include:
%F: displays the dateYYYY-MM-DDformat;%T: displays the time;%A: displays full weekday name;
To see a full list of specifiers, user the date --help or man date command.
You specify output format after the + sign:
$ date +'%F %T'
2018-09-23 05:31:21
$ date +%A
SundayYou will often see the date command to be used as part of the scripts for creating scheduled backups.
For example, the following command will create a backup of /home/vagrant/ directory and include the current date in the name of the resulting archive file:
$ tar cfz /backup-`date +%F`.tar.gz /home/vagrant/
$ ls /backup-2018-09-23.tar.gz
/backup-2018-09-23.tar.gz