Originální popis anglicky:
date - write the date and time
Návod, kniha: POSIX Programmer's Manual
date [-u] [+format]
date [-u]
mmddhhmm[[cc]yy]
The
date utility shall write the date and time to standard output
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.
The
date utility shall conform to the Base Definitions volume of
IEEE Std 1003.1-2001, Section 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.
The following operands shall be supported:
- +format
- When the format is specified, each conversion specifier
shall be replaced in the standard output by its corresponding value. All
other characters shall be copied to the output without change. The output
shall always be terminated with a <newline>.
- %a
- Locale's abbreviated weekday name.
- %A
- Locale's full weekday name.
- %b
- Locale's abbreviated month name.
- %B
- Locale's full month name.
- %c
- Locale's appropriate date and time representation.
- %C
- Century (a year divided by 100 and truncated to an integer)
as a decimal number [00,99].
- %d
- Day of the month as a decimal number [01,31].
- %D
- Date in the format mm/dd/yy.
- %e
- Day of the month as a decimal number [1,31] in a two-digit
field with leading space character fill.
- %h
- A synonym for %b .
- %H
- Hour (24-hour clock) as a decimal number [00,23].
- %I
- Hour (12-hour clock) as a decimal number [01,12].
- %j
- Day of the year as a decimal number [001,366].
- %m
- Month as a decimal number [01,12].
- %M
- Minute as a decimal number [00,59].
- %n
- A <newline>.
- %p
- Locale's equivalent of either AM or PM.
- %r
- 12-hour clock time [01,12] using the AM/PM notation; in the
POSIX locale, this shall be equivalent to %I : %M :
%S %p .
- %S
- Seconds as a decimal number [00,60].
- %t
- A <tab>.
- %T
- 24-hour clock time [00,23] in the format
HH:MM: SS.
- %u
- Weekday as a decimal number [1,7] (1=Monday).
- %U
- Week of the year (Sunday as the first day of the week) as a
decimal number [00,53]. All days in a new year preceding the first Sunday
shall be considered to be in week 0.
- %V
- Week of the year (Monday as the first day of the week) as a
decimal number [01,53]. If the week containing January 1 has four or more
days in the new year, then it shall be considered week 1; otherwise, it
shall be the last week of the previous year, and the next week shall be
week 1.
- %w
- Weekday as a decimal number [0,6] (0=Sunday).
- %W
- Week of the year (Monday as the first day of the week) as a
decimal number [00,53]. All days in a new year preceding the first Monday
shall be considered to be in week 0.
- %x
- Locale's appropriate date representation.
- %X
- Locale's appropriate time representation.
- %y
- Year within century [00,99].
- %Y
- Year with century as a decimal number.
- %Z
- Timezone name, or no characters if no timezone is
determinable.
- %%
- A percent sign character.
See the Base Definitions volume of IEEE Std 1003.1-2001, Section
7.3.5, LC_TIME for the conversion specifier values in the POSIX locale.
Some conversion specifiers can be modified by the
E and
O modifier
characters to indicate a different format or specification as specified in the
LC_TIME locale description (see the Base Definitions volume of
IEEE Std 1003.1-2001, Section 7.3.5, LC_TIME). If the
corresponding keyword (see
era,
era_year,
era_d_fmt, and
alt_digits in the Base Definitions volume of
IEEE Std 1003.1-2001, Section 7.3.5, LC_TIME) is not specified
or not supported for the current locale, the unmodified conversion specifier
value shall be used.
- %Ec
- Locale's alternative appropriate date and time
representation.
- %EC
- The name of the base year (period) in the locale's
alternative representation.
- %Ex
- Locale's alternative date representation.
- %EX
- Locale's alternative time representation.
- %Ey
- Offset from %EC (year only) in the locale's
alternative representation.
- %EY
- Full alternative year representation.
- %Od
- Day of month using the locale's alternative numeric
symbols.
- %Oe
- Day of month using the locale's alternative numeric
symbols.
- %OH
- Hour (24-hour clock) using the locale's alternative numeric
symbols.
- %OI
- Hour (12-hour clock) using the locale's alternative numeric
symbols.
- %Om
- Month using the locale's alternative numeric symbols.
- %OM
- Minutes using the locale's alternative numeric
symbols.
- %OS
- Seconds using the locale's alternative numeric
symbols.
- %Ou
- Weekday as a number in the locale's alternative
representation (Monday = 1).
- %OU
- Week number of the year (Sunday as the first day of the
week) using the locale's alternative numeric symbols.
- %OV
- Week number of the year (Monday as the first day of the
week, rules corresponding to %V ), using the locale's alternative
numeric symbols.
- %Ow
- Weekday as a number in the locale's alternative
representation (Sunday = 0).
- %OW
- Week number of the year (Monday as the first day of the
week) using the locale's alternative numeric symbols.
- %Oy
- Year (offset from %C ) in alternative
representation.
- mmddhhmm[[cc]yy]
-
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
IEEE Std 1003.1-2001 the default century inferred from a 2-digit
year will change. (This would apply to all commands accepting a 2-digit year
as input.)
Not used.
None.
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 the Base Definitions volume of
IEEE Std 1003.1-2001, Section 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
- Determine the location of message catalogs for the
processing of LC_MESSAGES .
- 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.
Default.
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"
The standard error shall be used only for diagnostic messages.
None.
None.
The following exit values shall be returned:
- 0
- The date was written successfully.
- >0
- An error occurred.
Default.
The following sections are informative.
Conversion specifiers are of unspecified format when not in the POSIX locale.
Some of them can contain <newline>s 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.
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:
would yield 3.IX.1991. With the same
d_fmt, but without the
alt_digits, the command would yield 3.9.1991.
- 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
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 8601:2000 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.
None.
The System Interfaces volume of IEEE Std 1003.1-2001,
printf(),
strftime()
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.opengroup.org/unix/online.html
.
