date

Set, display and manipulate dates
To view / specify the timezone, use timedatectl

Flag	Usage
(none)	display the current date and time : Wed Aug 5 09:35:06 CEST 2015 you can specify the output format
-d dateString --date dateString	instruct date to work with dateString rather than with the current date+time. This is used mostly to compute dates+times extract date+time fields : month number, hour, number of seconds, dateString : can be the result of a previous date invocation provided its format matches "what we want to do with it" (not clear to me yet ) see example : use a common timestamp to compute start + end timestamps date jeu. 10 oct. 2024 09:00:37 CEST date -d $(date +%F) +%Y 2024 date -d $(date +%F) +%S ⇐ all OK 00 date -d $(date +%F) +%a jeu. date -d $(date) +%Y date: extra operand ‘oct.’ Try 'date --help' for more information. ⇐ KO date -d "$(date)" +%Y date: invalid date ‘jeu. 10 oct. 2024 09:04:25 CEST’ rightNow=$(date +%F); seconds=$(date -d "$rightNow" +%S); echo "right now : '$rightNow', seconds : '$seconds'" right now : '2024-10-10', seconds : '00' ⇐ always '00' if seconds are missing in the input rightNow=$(date '+%F %H:%M:%S'); seconds=$(date -d "$rightNow" +%S); echo "right now : '$rightNow', seconds : '$seconds'" right now : '2024-10-10 10:02:19', seconds : '19' ⇐ OK can use keywords such as now, yesterday, today, tomorrow, day(s), week(s), month(s), year(s), : date --date "-60 days" unsigned integers are interpreted as +n if the start date is omitted, +n / -n are relative to now : date --date 'now -60 days'; date --date '-60 days' it is possible to combine different units : date --date='now'; date --date='-23hour'; date --date='-1day +1hour' date --date=tomorrow date -d "2023-01-29 +42days" for unitOfTime in day week month year; do for number in {1..3}; do echo -en "+$number$unitOfTime :\t"; date --date "now +$number$unitOfTime"; done; done more about date strings
--iso-8601 --iso-8601=precision	display date/time using the ISO 8601 format : date; for precision in date hours minutes seconds ns; do echo -n "$precision : "; date --iso-8601="$precision"; done Fri 11 Mar 2022 09:10:22 AM CET just date, for comparison date : 2022-03-11 default precision hours : 2022-03-11T09+01:00 up to the current hour minutes : 2022-03-11T09:10+01:00 up to the current hour:minute seconds : 2022-03-11T09:10:22+01:00 up to the current hour:minute:second ns : 2022-03-11T09:10:22,111460006+01:00 up to the current hour:minute:second,nanosecond
-r file --reference file	display the last modification time of file
-s dateString --set dateString	set time described by dateString : date --set="Oct 31 10:52:40"

Date strings (source) :

For full details :

run info '(coreutils) date invocation'
then select Date input formats | Relative items in date strings

The --date='dateString' is a human-readable format such as next Thursday or 1 month ago. A date string may contain items indicating :

calendar date
time of day
time zone
day of the week
relative time
relative date
numbers

Keywords

now is a synonym of today. Check it : date --date now; date --date today
tomorrow is today + 24 hours. The same goes on with yesterday and today. Check it : date --date yesterday; date --date today; date --date tomorrow

Examples

The commands below were run on the Friday 19^th of July.

the basics

date
Fri 19 Jul 2019 11:17:29 AM CEST
date --date="today"			same as above
Fri 19 Jul 2019 11:17:44 AM CEST
date --date="tomorrow"
Sat 20 Jul 2019 11:17:54 AM CEST
date --date="next monday"
Mon 22 Jul 2019 12:00:00 AM CEST
date; TZ=GMT date			display current date+time in a different time zone
Tue Feb 20 09:32:07 AM CET 2024
Tue Feb 20 08:32:07 AM GMT 2024

dates in the future / in the past

date --date="3 days"
Mon 22 Jul 2019 11:22:13 AM CEST
date --date="3 days ago"		ago ...
Tue 16 Jul 2019 11:22:19 AM CEST
date --date="-3 days"			and negative values compute dates in the past ...
Tue 16 Jul 2019 11:22:25 AM CEST
date --date="-3 days ago"		unless you combine both 
Mon 22 Jul 2019 11:37:53 AM CEST
date --date="-1 year month"
Sun 19 Aug 2018 12:32:02 PM CEST	+1 is implied for units without a number

(void) / this / next

date --date="thursday"
Thu 25 Jul 2019 12:00:00 AM CEST
date --date="this thursday"
Thu 25 Jul 2019 12:00:00 AM CEST
date --date="next thursday"
Thu 25 Jul 2019 12:00:00 AM CEST

date --date="friday"
Fri 19 Jul 2019 12:00:00 AM CEST
date --date="this friday"
Fri 19 Jul 2019 12:00:00 AM CEST
date --date="next friday"
Fri 26 Jul 2019 12:00:00 AM CEST

date --date="saturday"
Sat 20 Jul 2019 12:00:00 AM CEST
date --date="this saturday"
Sat 20 Jul 2019 12:00:00 AM CEST
date --date="next saturday"
Sat 20 Jul 2019 12:00:00 AM CEST

(void) implies this
this weekDay means :
- if today is a weekDay : the current day
- otherwise : next weekDay

future weekdays :

date --date="next monday"
Mon 22 Jul 2019 12:00:00 AM CEST
date --date="1 monday"			same as next
Mon 22 Jul 2019 12:00:00 AM CEST
date --date="2 monday"
Mon 29 Jul 2019 12:00:00 AM CEST
date --date="second monday"		second is "1 second", not "the second from now"
Mon 22 Jul 2019 12:00:01 AM CEST
date --date="third monday"
Mon 05 Aug 2019 12:00:00 AM CEST
date --date="fourth monday"
Mon 12 Aug 2019 12:00:00 AM CEST
date --date="tenth monday"
Mon 23 Sep 2019 12:00:00 AM CEST

a specific timestamp in order to compute accurate start + end timestamps

You may run :
outputFormat='+%F %H:%M:%S'; startTime=$(date "$outputFormat"); endTime=$(date -d '+2years' "$outputFormat"); echo -e "start :\t$startTime\nend :\t$endTime"
which outputs values that are split by 2 full years (same second ) and is fine 99.99999999% of the time :
```
start : 2024-12-05 15:37:40
end :   2026-12-05 15:37:40
```
But if you run :
outputFormat='+%F %H:%M:%S.%N'; startTime=$(date "$outputFormat"); endTime=$(date -d '+2years' "$outputFormat"); echo -e "start :\t$startTime\nend :\t$endTime"
you get :
```
start : 2024-12-05 15:50:47.065296725
end :   2026-12-05 15:50:47.067093474
```
which is milliseconds away from the exact "start +2years". This is because :
- startTime is "now"
- endTime is based on "now" + a delay, but this "now" occurred a blink after the "now" of startTime, hence the difference.
I've never encountered a situation where it mattered, but for the sake of completeness, let's say it does, and continue
Now let's run :
outputFormat='+%F %H:%M:%S.%N %Z'; currentDateTime=$(date "$outputFormat"); startTime=$(date -d "$currentDateTime" "$outputFormat"); endTime=$(date -d "$currentDateTime +2years" "$outputFormat"); echo -e "start :\t$startTime\nend :\t$endTime"
```
start : 2024-12-05 16:07:50.159780462 CET
end :   2026-12-05 16:07:50.159780462 CET
```
For an unknown reason, if $currentDateTime has no timezone field (%Z), the computed value for $endTime is effectively after $startTime, but not by the specified delay.

Output format :

full list : man -P 'less -p "^ *FORMAT "' date
GMT, CET, CEST, Z, , are known as Time Zone Abbreviations. View list :
- timeanddate.com
- Wikipedia

Output	Format string	Usage
20170201	date +%Y%m%d	compact representation of a date that can be used in a filename
20181116_152852	date +%Y%m%d_%H%M%S
2018-11-29 15:51:36	date '+%F %H:%M:%S'	Quotes are necessary when the format string has a space, otherwise you'll get a date: extra operand '%H:%M:%S' error message. %F is a synonymous of %Y-%m-%d
2024-04-25	date +%F date --iso-8601
2011-12-29_10-23-08	date +%F_%H-%M-%S	(almost) same as above except the `:` changed to `_`, which is better if this timestamp is part of a filename
1014	date +%H%M	at time format
jeu., 28 nov. 2013 15:10:46 GMT	date +"%a, %d %b %Y %H:%M:%S GMT"	If-Modified-Since HTTP header date format
1387202860	date +%s	Unix timestamp, see examples
Wed Mar 15 Fri Sep 1	date +"%a %b %-d"	git log date format the extra `-` prevents padding the day number with a leading 0 if <10. this format ignores the year, which may have unexpected results if the Git history has commits on the "same day" of distinct years (which happened to me with Wed Dec 12 of 2018 and 2012)
Fri Mar 13 17:35:03 2020 +0100	date +"%a %b %-d %H:%M:%S %Y %z"	git log long date format (depending on personal settings / aliases /...)
CEST +0200	date +"%Z %z"	current timezone : alphabetic abbreviation, then numeric
16:22:22.056139331	date '+%H:%M:%S.%N'	display nanoseconds

Convert dates :

Date string YYYY-MM-DD hh:mm:ss to Unix timestamp :

date -d '2013-10-24 14:35:55' +%s

1382618155

Unix timestamp to date :

date -d @1387215550 '+%d/%m/%Y - %H:%M'
```
16/12/2013 - 18:39
```

for unixTime in 1234567890 1500000000 1600000000 2000000000; do echo -e "UNIX time : $unixTime\t==>\tLOCAL TIME : $(date -d @$unixTime)"; done

UNIX time : 1234567890	==>	LOCAL TIME : Sat Feb 14 00:31:30 CET 2009		Central European Time
UNIX time : 1500000000	==>	LOCAL TIME : Fri Jul 14 04:40:00 CEST 2017
UNIX time : 1600000000	==>	LOCAL TIME : Sun Sep 13 14:26:40 CEST 2020		Central European Summer Time, nothing's wrong with date 
UNIX time : 2000000000	==>	LOCAL TIME : Wed May 18 05:33:20 CEST 2033

Compute the end of Epoch (source) :

date -d @$(echo $((2 ** 31 - 1)))

Compute the number of days since any past date :

echo "scale=3; ("$(date -d"now" +%s) - $(date -d"2016-12-18 10:05:00" +%s)") / 86400" | bc

Compute the number of days between 2 dates :

general case :

startDate='2016-12-18 10:05:00'; endDate='today'; echo "scale=1; ("$(date --date "$endDate" +%s) - $(date --date "$startDate" +%s)") / 86400" | bc

excluding start and end days :

startDate='yesterday'; endDate='tomorrow'; echo "scale=1; ("$(date --date "$endDate 00:00:00" +%s) - $(date --date "$startDate 23:59:59" +%s)") / 86400" | bc
startDate='20170330'; endDate='20170401'; printf %0.f $(echo "scale=1; ("$(date --date "$endDate" +%s) - $(date --date "$startDate" +%s)") / 86400 -1" | bc)

go even further :

There's a hack to compute dates with integers only, which makes the whole command not exact if there's an odd number of days .

Compute an end date while still considering workdays and week-ends :

This is typically the kind of questions we face once having determined a list of tasks and their durations, and now having to plan all these.

I am convinced it would be possible to do this with date + Bash (believe me, I like scripting ! ), but in the light of getting-results-fast, LibreOffice Calc's workday function wins !
For those wondering, Excel has a similar workday function.

Travel back in time (and in logfiles) :

startYear='2014'
startMonth='08'
startDay='06'

startHour='13'
startMinute='00'
startSecond='00'

nbDaysBack=4
resolutionInHours=1	# number of hours between 2 generated datetimes

#dateTimeFormat='%d%m%y-%H'	# ddmmyy-hh
dateTimeFormat='%Y-%m-%d %H'	# yyyy-mm-dd hh

initialTimestamp=$(date -d"$startYear-$startMonth-$startDay $startHour:$startMinute:$startSecond" +%s)
nbLoops=$((24/$resolutionInHours*$nbDaysBack))
timestamp=$initialTimestamp
for i in $(seq 1 $nbLoops);do
	formattedDate=$(date -d@$timestamp +"$dateTimeFormat")
	echo $formattedDate

	# ... now do something smart with the formatted date !

	timestamp=$((timestamp-(3600*$resolutionInHours)))
done

date - Today is tomorrow's yesterday.

Usage

Flags