NAME

date — write the date and time

SYNOPSIS

date [-u] [+format]



[XSI] date [-u] mmddhhmm[[cc]yy]

DESCRIPTION

The date utility shall write the date and time to standard output ^[XSI]  or attempt to set the system date and time. By default, the current date and time shall be written. If an operand beginning with '+' is specified, the output format of date shall be controlled by the conversion specifications and other text in the operand.

OPTIONS

The date utility shall conform to XBD 12.2 Utility Syntax Guidelines.

The following option shall be supported:

-u

Perform operations as if the TZ environment variable was set to the string "UTC0", or its equivalent historical value of "GMT0". Otherwise, date shall use the timezone indicated by the TZ environment variable or the system default if that variable is unset or null.

OPERANDS

The following operands shall be supported:

+format

When the format is specified, the output shall be formatted as if by strftime() with the specified format string, and a timeptr argument that is the equivalent of localtime(&now) if -u is not specified or gmtime(&now) if -u is specified, where now is an object of type time_t containing the return value of time(0).

A <newline> shall always be appended to the output of strftime().

mmddhhmm[[cc]yy]

^[XSI]
Attempt to set the system date and time from the value given in the operand. This is only possible if the user has appropriate privileges and the system permits the setting of the system date and time. The first mm is the month (number); dd is the day (number); hh is the hour (number, 24-hour system); the second mm is the minute (number); cc is the century and is the first two digits of the year (this is optional); yy is the last two digits of the year and is optional. If century is not specified, then values in the range [69,99] shall refer to years 1969 to 1999 inclusive, and values in the range [00,68] shall refer to years 2000 to 2068 inclusive. The current year is the default if yy is omitted.

Note:

It is expected that in a future version of this standard the default century inferred from a 2-digit year will change. (This would apply to all commands accepting a 2-digit year as input.)

STDIN

Not used.

INPUT FILES

None.

ENVIRONMENT VARIABLES

The following environment variables shall affect the execution of date:

LANG

Provide a default value for the internationalization variables that are unset or null. (See XBD 8.2 Internationalization Variables for the precedence of internationalization variables used to determine the values of locale categories.)

LC_ALL

If set to a non-empty string value, override the values of all the other internationalization variables.

LC_CTYPE

Determine the locale for the interpretation of sequences of bytes of text data as characters (for example, single-byte as opposed to multi-byte characters in arguments).

LC_MESSAGES

Determine the locale that should be used to affect the format and contents of diagnostic messages written to standard error.

LC_TIME

Determine the format and contents of date and time strings written by date.

NLSPATH

^[XSI] Determine the location of messages objects and message catalogs.

TZ

Determine the timezone in which the time and date are written, unless the -u option is specified. If the TZ variable is unset or null and -u is not specified, an unspecified system default timezone is used.

ASYNCHRONOUS EVENTS

Default.

STDOUT

When no formatting operand is specified, the output in the POSIX locale shall be equivalent to specifying:

date "+%a %b %e %H:%M:%S %Z %Y"

STDERR

The standard error shall be used only for diagnostic messages.

OUTPUT FILES

None.

EXTENDED DESCRIPTION

None.

EXIT STATUS

The following exit values shall be returned:

 0

The date was written successfully.

>0

An error occurred.

CONSEQUENCES OF ERRORS

Default.

APPLICATION USAGE

Conversion specifiers are of unspecified format when not in the POSIX locale. Some of them can contain <newline> characters in some locales, so it may be difficult to use the format shown in standard output for parsing the output of date in those locales.

Since the default date utility format for locales other than the POSIX or C locale is not required to include anything beyond the date and time, whereas for the POSIX or C locale it also includes the day name and time zone, it may be necessary to specify a format (or override the locale-selection environment variables) to ensure this information is included when desired.

The range of values for %S extends from 0 to 60 seconds to accommodate the occasional leap second.

Although certain of the conversion specifiers in the POSIX locale (such as the name of the month) are shown with initial capital letters, this need not be the case in other locales. Programs using these fields may need to adjust the capitalization if the output is going to be used at the beginning of a sentence.

The date string formatting capabilities are intended for use in Gregorian-style calendars, possibly with a different starting year (or years). The %x and %c conversion specifications, however, are intended for local representation; these may be based on a different, non-Gregorian calendar.

The %C conversion specification was introduced to allow a fallback for the %EC (alternative year format base year); it can be viewed as the base of the current subdivision in the Gregorian calendar. The century number is calculated as the year divided by 100 and truncated to an integer; it should not be confused with the use of ordinal numbers for centuries (for example, "twenty-first century".) Both the %Ey and %y can then be viewed as the offset from %EC and %C, respectively.

The E and O modifiers modify the traditional conversion specifiers, so that they can always be used, even if the implementation (or the current locale) does not support the modifier.

The E modifier supports alternative date formats, such as the Japanese Emperor's Era, as long as these are based on the Gregorian calendar system. Extending the E modifiers to other date elements may provide an implementation-defined extension capable of supporting other calendar systems, especially in combination with the O modifier.

The O modifier supports time and date formats using the locale's alternative numerical symbols, such as Kanji or Hindi digits or ordinal number representation.

Non-European locales, whether they use Latin digits in computational items or not, often have local forms of the digits for use in date formats. This is not totally unknown even in Europe; a variant of dates uses Roman numerals for the months: the third day of September 1991 would be written as 3.IX.1991. In Japan, Kanji digits are regularly used for dates; in Arabic-speaking countries, Hindi digits are used. The %d, %e, %H, %I, %m, %S, %U, %w, %W, and %y conversion specifications always return the date and time field in Latin digits (that is, 0 to 9). The %O modifier was introduced to support the use for display purposes of non-Latin digits. In the LC_TIME category in localedef, the optional alt_digits keyword is intended for this purpose. As an example, assume the following (partial) localedef source:

alt_digits  "";"I";"II";"III";"IV";"V";"VI";"VII";"VIII" \
            "IX";"X";"XI";"XII"
d_fmt       "%e.%Om.%Y"

With the above date, the command:

date "+%x"

would yield 3.IX.1991. With the same d_fmt, but without the alt_digits, the command would yield 3.9.1991.

EXAMPLES

1. The following are input/output examples of date used at arbitrary times in the POSIX locale:

   $ date
   Tue Jun 26 09:58:10 PDT 1990
   
   
   $ date "+DATE: %m/%d/%y%nTIME: %H:%M:%S"
   DATE: 11/02/91
   TIME: 13:36:16
   
   
   $ date "+TIME: %r"
   TIME: 01:36:32 PM
   

2. Examples for Denmark, where the default date and time format is %a %d %b %Y %T %Z:

   $ LANG=da_DK.iso_8859-1 date
   ons 02 okt 1991 15:03:32 CET
   
   
   $ LANG=da_DK.iso_8859-1 \
       date "+DATO: %A den %e. %B %Y%nKLOKKEN: %H:%M:%S"
   DATO: onsdag den 2. oktober 1991
   KLOKKEN: 15:03:56
   

3. Examples for Germany, where the default date and time format is %a %d.%h.%Y, %T %Z:

   $ LANG=De_DE.88591 date
   Mi 02.Okt.1991, 15:01:21 MEZ
   
   
   $ LANG=De_DE.88591 date "+DATUM: %A, %d. %B %Y%nZEIT: %H:%M:%S"
   DATUM: Mittwoch, 02. Oktober 1991
   ZEIT: 15:02:02
   

4. Examples for France, where the default date and time format is %a %d %h %Y %Z %T:

   $ LANG=Fr_FR.88591 date
   Mer 02 oct 1991 MET 15:03:32
   
   
   $ LANG=Fr_FR.88591 date "+JOUR: %A %d %B %Y%nHEURE: %H:%M:%S"
   JOUR: Mercredi 02 octobre 1991
   HEURE: 15:03:56
   

RATIONALE

Some of the new options for formatting are from the ISO C standard. The -u option was introduced to allow portable access to Coordinated Universal Time (UTC). The string "GMT0" is allowed as an equivalent TZ value to be compatible with all of the systems using the BSD implementation, where this option originated.

The %e format conversion specification (adopted from System V) was added because the ISO C standard conversion specifications did not provide any way to produce the historical default date output during the first nine days of any month.

There are two varieties of day and week numbering supported (in addition to any others created with the locale-dependent %E and %O modifier characters):

• The historical variety in which Sunday is the first day of the week and the weekdays preceding the first Sunday of the year are considered week 0. These are represented by %w and %U. A variant of this is %W, using Monday as the first day of the week, but still referring to week 0. This view of the calendar was retained because so many historical applications depend on it and the ISO C standard strftime() function, on which many date implementations are based, was defined in this way.

• The international standard, based on the ISO 8601:2019 standard where Monday is the first weekday and the algorithm for the first week number is more complex: If the week (Monday to Sunday) containing January 1 has four or more days in the new year, then it is week 1; otherwise, it is week 53 of the previous year, and the next week is week 1. These are represented by the new conversion specifications %u and %V, added as a result of international comments.

Although this standard only requires the default date utility format, for locales other than the POSIX or C locale, to include the date and time, it is common for implementations to include day name and time zone information as well. (For the POSIX locale this is required, with the day name in %a format at the beginning and the time zone in %Z format before the year.) Implementations are encouraged to include the day name (in %a or %A format) and the time zone (in %Z or %z format) in the default date utility format for all of the locales they provide.

Some implementations have a date_fmt locale keyword (see 7.3.5 LC_TIME) as an extension, to specify the default date utility format for each locale. On such implementations, if the localedef utility is used to create a locale that does not have this information, the date utility must by default still produce output for that locale that includes both the time and the date.

FUTURE DIRECTIONS

None.

SEE ALSO

XBD 7.3.5 LC_TIME, 8. Environment Variables, 12.2 Utility Syntax Guidelines

XSH fprintf, strftime

CHANGE HISTORY

First released in Issue 2.

Issue 5

Changes are made for Year 2000 alignment.

Issue 6

The following new requirements on POSIX implementations derive from alignment with the Single UNIX Specification:

• The %EX modified conversion specification is added.

The Open Group Corrigendum U048/2 is applied, correcting the examples.

The DESCRIPTION is updated to refer to conversion specifications, instead of field descriptors for consistency with the LC_TIME category.

A clarification is made such that the current year is the default if the yy argument is omitted when setting the system date and time.

IEEE Std 1003.1-2001/Cor 1-2002, item XCU/TC1/D6/19 is applied, correcting the CHANGE HISTORY section.

Issue 8

Austin Group Defect 466 is applied, replacing the list of conversion specifications for the +format operand with a requirement that the output is formatted as if by a call to strftime() with specific arguments.

Austin Group Defect 1122 is applied, changing the description of NLSPATH .

Austin Group Defect 1345 is applied, adding paragraphs to APPLICATION USAGE and RATIONALE about the default date utility format.