Display or set date and time

Green
options
not BSD
not mac os

java Script

date [-nu] [-r file] [ +format]

date [-jnRu] [-d ¬ datestring| --date= datestring] [-r seconds] [-t west] [-v[+|-]val[ymwdHMS]] …
             [-f | fmt date | --file=fileOfDates
      [[[mm]dd]HH]MM[[cc]yy][.ss]] [+format]

date -d n -t minutes_west date [[[[[cc]yy]mm]dd]hh]mm[.ss]      # set system time

The default format is: "%a %b %e %H:%M:%S %Z %Y"
sample output: Sat Dec 31 18:09:28 EST 2021

Useful forms:
date "+%y-%m-%d_%H:%M:%S $0 started with $*" >> %y%m%d-%H%M.log
export TODAY=`date +%y%m%d`
quotes are unneeded as format does not include space etc		echo $TODAY
221231
export yymmdd=`date +%y%m%d` echo $yymmdd
130915
export LOG=`date +log/%y%m%d.%H%M` echo $LOG
log/211231.1859

myscript1 >> $LOG
myscript2 >> $LOG

date "+%m-%d %H:%M:%S birdloger.cgi starts" >> birdloger.cgi.log

export title=`date +"Report Date: %m/%d %H:%M"` Report Date: 07/20 18:56

echo `date "+%Y-%m-%d %H:%M:%S"` 2018-12-31 23:59:59 (Similar to linux syslog formats.)
touch `date +"%F_%T"` creates files named yy-mm-dd_hh:mm:ss
I forget why this is interesting!

format codes
(arranged by function, not alphabetically, composite formats)

   N.B. If used in crontab command fields, % must be escaped.

Items which vary by

locale

 Order of date items vary
Spellings as per language.
Examples:
LC_ALL=C
 > date
Wed Jun 22 13:18:10 EDT 2016
 > export LC_ALL=es_ES  # use Spanish (Español)
 > date
miércoles, 22 de junio de 2016, 13:39:34 EDT
%m mm month (01…12)
to blank pad ie ' 1, 2, 3' vs '01,02,03' ?? ) sed s/0([[:digit:]])/ $1/
%b abbreviated month (Jan…Dec) %h (same as:%b)
%B full month, variable length (January…December)
%d dd (01…31), %e ( ' 1'…'31')
%C cc century (00…99) %y yy two digit year (00…99)
%Y ccyy year (1970)
%F %Y-%m-%d (2013-02-24)
%y%m%d (241231)
%D mm/dd/yy %x mm/dd/yy
%g 2-digit year corresponding to the %V week number %G 4-digit

Time

%I (01…12) %H (00…23)
%l† (1…12)  %k (0…23)
%p AM or PM upper case (blank in many locales)   %P am or pm lower case
%M MM minutes (00…59)
%S SS second (00…60) The 60 is necessary to accommodate a leap second
%H%M%S 235958
24-hour: %R (23:59), %T HH:mm:ss ( 11:53:41 )
12-hour: %r (11:26:20 AM )
%X %H:%M:%S (11:56:05 AM)
%c date and time (Sat Nov 04 12:02:33 EST 1989 )
%N nanoseconds † since last second (000000000..999999999)
(on mac OS use gdate )
     Use sed to restrict the output to milliseconds:
date +%S.%N|sed "s/......$//" 26.123 


%j     day of year (001…366) 

%u     day of week (1…7);  7 represents Sunday mtwtfss     

%w                    (0…6);  0 represents Sunday smtwtfs 

%a     abbreviated weekday (Sun…Sat) 

%A     full weekday, variable length (Sunday…Saturday) 

%U     week number  Sunday as first day of week (00…53) 

%W     week number  Monday as first day of week (00…53)        %V    (01…53) 

%z     -zzzz      RFC-822 style numeric timezone (-0400) 

 %:z    +hh:mm numeric timezone ( -04:00) 

 %::z   +hh:mm:ss numeric time zone ( -04:00:00)
 

 %:::z  numeric time zone with : to necessary precision (-04, +05:30) 

%Z     time zone (EDT) nothing if  no  time  zone  is  determinable

$TZ     timezone, unless overridden by command line parameters.

Default: the setting from /etc/localtime is used. 

on macBookPro:
     > hexdump -e  '"%_p"' -s 0x4DB -n 7   /etc/localtime
     EDT.EST

On Real-World-Systems.com
     hexdump -e  '"%_p"'    /etc/localtime |tail -2
     .MST7MDT,M3.2.0,M1*

     > echo $TZ
     America/Boise
     > date
     Wed Mar 27 18:36:50 MDT 2019

     export TZ=US/Eastern 
     > echo $TZ
     US/Eastern
     > date
     Wed Mar 27 20:37:00 EDT 2019





%s seconds since 00:00:00 1970-01-01 UTC i.e. epoch

To convert %s value like           10 1212642879 

 use date -d "1970-01-01 1212642879 sec utc" Not mac 


  1264434947 was Mon Jan 25 10:55:57 EST 2010
  1402410634 was Tue Jun 10 10:29:44 EDT 2014


Example usage: 

export login_s=`date +%s`  # include this in .profile



#      ~/.bash_logout
echo " $(((`date +%s` - $login_s)/60))  minutes"
sleep 3 

 
literals:  %n  newline    ;  %% percent; %t horizontal tab 



By  default, date pads numeric fields with zeroes.  


GNU (not BSD) date recognizes modifiers between % and a numeric: 

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

 examples:  

%_H == %k          %-m/%-d/%y    1/2/50







 Options









 
            -d string



            -de=string		
Display time described by string 

Including some "humand readable" strings like last Thursday and last month

date -d "2010/12/31"              Fri Dec 31 00:00:00 EST 2010
date -d "12/31/2010"              Fri Dec 31 00:00:00 EST 2010
date -d "2010-12-31 23:58:57"     Fri Dec 31 23:58:57 EST 2010
date -d "23:58:57 12/31/2010"     Fri Dec 31 23:58:57 EST 2010
date -d "12/31/2010 23:58:57"     Fri Dec 31 23:58:57 EST 2010
date -d "12/31/2010 23 sec"       Fri Dec 31 00:00:23 EST 2010 

To convert seconds (for example 1212642879) use: 

> date -d "1970-01-01 1212642879 sec utc"

Thu Jun  5 01:14:39 EDT 2008



  




-e=datefile like -de once for each line of datefile



 BSD(Mac OS X):


-f fmt_str idate [ +fmt] Output idate

Default fmt_str is  [[[mm]dd]HH]MM[[cc]yy][.ss]

 -j with -f Don't set 






date and time seconds from the Epoch. ( i.e. Dec 31 19:00:00 EST 1969 i.e. 01/01/70 00:00:00)




       
-r secondsSinceEpochi Use  secondsSinceEpoch instead of current time
       
-r file     
 
--reference=file     		output modification date/time of file 

         > date -r 0test 
         Thu Aug 19 18:05:09 EDT 2010

         > date -r arp.1.html +"%y%m%d_%H%M"
         140630_1810




  -v [±]value​m|d|H|M|S|w

 -v{±]name
 Output the current date adjusted by ± value months, days, hours, Minutes, Seconds or weeks.

Suffix is required (with no preceeding space) 

name is a case in-sensitive, 3 character or longer week_day or month (example Tue June).


If a name is used with a sign, the date will be adjusted forwards (or backwards) to the next (previous) date 
that matches the given week day or month.  

If the given week day or month is the same as the current one no adjustment is made.  

Multiple -v options are permitted.
% date
Fri Feb 21 17:54:06 EST 2025
date -v +tue   # i.e. next Tuesday
Tue Feb 25 17:54:06 EST 2025
% date -v +tue -v +3H
Tue Feb 25 20:54:06 EST 2025 



Attempting to  set or adjust a date to an invalid day fails with return code of 1. 

For example: -v 31d, for months having less than 31 days. 

To minimize this problem, set the minutes first then the day, for example: -v 12m -v 31d    


Adjusting by months is ambiguous because months have varying numbers of days.

Adjusting the month on the 31st,  if the target month is shorter than the present one, 
will result in using the last day of the target month.  

For example, using -v +1m on May 31 will adjust the date to June 30, 

For y the value must be in the range of 80-38 or 1980-2038, otherwise return code will be 1.
 
Multiple -ts are permitted.




-u

--utc

--universal [MMDDhhmm[[CC]YY][.ss]] 		
aka GMT 
Sun Jun 27 21:56:05 UTC 2021
Sat Feb 5 14:49:42 GMT 2005




-I[precision]

--iso-8601[=precision] 		output in ISO 8601 format. 

precision : date |  hours |  minutes |  seconds 
| ns

> date --iso-8601               2010-08-23
> date --iso-8601=hours         2010-08-23T21-0400
> date --iso-8601=minutes       2010-08-23T21:05-0400
> date --iso-8601=seconds       2010-08-23T21:05:53-0400 
> date --iso-8601=ns            2010-08-23T21:05:53,632672872-04:00


-R 

--rfc-822         		output RFC-822 compliant date string

                                     Sun, 23 Aug 2010 21:53:18 -0400



 -s string

--set=string 		set the system the clock to string

                        Example: date -s "2010-12-31 23:59:00"


 
-d dst Set kernel  value for daylight saving time. 

-n      No synchroniztion of clocks on groups of machines using timed.  

          Default: if timed is running, date will set the time on all of the machines in the local group,

  -n inhibites that.

 --help display help and exit 
       
--version output version information and exit








 
Daylight Saving Time
 
Daylight savings time considerations are ignored when a date is set/adjusted to a value or adjusted in units greater than hours.
Daylight saving time is honored with Adjustments in units of hours or less .  

For example:

If the current date is March 26, 00:30 and the DST adjustment means the clock goes forward at 01:00 to 02:00,
using -v +1H will adjust the date to March 26, 02:30.  

if the date is October 29, 00:30 and the DST adjustment means that
             the clock goes back at 02:00 to 01:00, -v +3H is necessary to reach October 29, 02:30.


If the date is adjusted to a value that does not exist (due to day light savings time, for example March 26, 01:30 BST 2000
in the Europe/London timezone), the date will be adjusted forwards in units of one hour until it reaches a valid time

If the date is adjusted to a value that occurs twice (for example October 29, 01:30 2000),
    the resulting timezone will be set so that the date matches the earlier of the two times.




 see also
 
strftime



java script functions

From w3schools.com




according to 

UTC (aka GMT)



Max  00 1F FF FF   FF FF FF FF aka 9,007,199,254,740,991
date object is local 

  
 getMonth()   0-11
     getUTCMonth() 

 getDate()  day of the month ( 1-31)
     getUTCDate()
  
 getFullYear()  year yyyy
     getUTCFullYear()
    
 getHours()  0-23
     getUTCHours()

 getMinutes()  0-59
     getUTCMinutes()
  
 getSeconds()   0-59
     getUTCSeconds() 

 getMilliseconds()  0-999
     getUTCMilliseconds() 

 getDay()  of the week ( 0-6)
     getUTCDay()
    
 getTime()  milliseconds since  1/1/1970 00:00
    
 getTimezoneOffset()  minutes between UTC and local 
  
 getYear() Deprecated. Use the getFullYear() method 
  
 parse() number of milliseconds since 1/1/1970 00:00  of date string 

set portions of a date object

 setFullYear()  YYYY
     setUTCFullYear()

 setMonth()  
setUTCMonth()
  
 setDate()  day of the month 
setUTCDate()
    
 setHours()  
setUTCHours()
    
 setMinutes() 
setUTCMinutes()
  
 setSeconds()  
setUTCSeconds()

 setMilliseconds() 
setUTCMilliseconds() 
    
 setTime() Sets a date and time 

by adding or subtracting milliseconds to/from  1/1/1970 00:00 
  
 setYear() Deprecated. Use the setFullYear() method 


formatting to string
    
 toString() Sat Aug 04 2012 17:09:15 GMT-0400 (EDT)
toLocaleString() Sat Aug  4 17:08:41 2012 

                        Really! YYYY last

    
 toISOString() 
2012-08-04T21:03:51.449Z
    
 toJSON() 

JavaScript Object Notation
2012-08-04T20:27:42.419Z

  
 toUTCString() Sat, 04 Aug 2012 21:32:18 GMT
  
 toDateString() Sat Aug 04 2012
     toLocaleDateString() 08/04/2012 

    
 toTimeString() 17:14:24 GMT-0400 (EDT)
toLocaleTimeString() 17:06:00

    
 toGMTString() Deprecated. Use the toUTCString() method 
  
 valueOf()  primitive value of a Date object
1344116221551
  
 UTC(yyyy,mm,dd)  number of milliseconds in yyyy,mm,dd

since 00:00 1/1/1970
 according to universal time
1333065600000