date.html

unix 下的C开发手册,还用详细的例程。

characters (for example, single- as opposed to multi-byte characters
in arguments).

<dt><i>LC_MESSAGES</i><dd>
Determine the locale that should be used to affect
the format and contents of diagnostic
messages written to standard error.

<dt><i>LC_TIME</i><dd>
Determine the format and contents of date and time
strings written by
<i>date</i>.

<dt><i>NLSPATH</i><dd>
Determine the location of message catalogues
for the processing of
<i>LC_MESSAGES .
</i>
<dt><i>TZ</i><dd>Determine the timezone in which the time and date are
written, unless the
<b>-u</b>
option is specified.
If the
<i>TZ</i>
variable is not set and the
<b>-u</b>
is not specified, an unspecified system default timezone is used.

</dl>
</blockquote><h4><a name = "tag_001_014_347">&nbsp;</a>ASYNCHRONOUS EVENTS</h4><blockquote>
Default.
</blockquote><h4><a name = "tag_001_014_348">&nbsp;</a>STDOUT</h4><blockquote>
When no formatting operand is specified, the output
in the POSIX locale is equivalent to specifying:
<pre>
<code>
date "+%a %b %e %H:%M:%S %Z %Y"
</code>
</pre>
</blockquote><h4><a name = "tag_001_014_349">&nbsp;</a>STDERR</h4><blockquote>
Used only for diagnostic messages.
</blockquote><h4><a name = "tag_001_014_350">&nbsp;</a>OUTPUT FILES</h4><blockquote>
None.
</blockquote><h4><a name = "tag_001_014_351">&nbsp;</a>EXTENDED DESCRIPTION</h4><blockquote>
None.
</blockquote><h4><a name = "tag_001_014_352">&nbsp;</a>EXIT STATUS</h4><blockquote>
The following exit values are returned:
<dl compact>

<dt>0<dd>The date was written successfully.

<dt>&gt;0<dd>An error occurred.

</dl>
</blockquote><h4><a name = "tag_001_014_353">&nbsp;</a>CONSEQUENCES OF ERRORS</h4><blockquote>
Default.
</blockquote><h4><a name = "tag_001_014_354">&nbsp;</a>APPLICATION USAGE</h4><blockquote>
Field descriptors 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
<i>date</i>
in those locales.
<p>
The range of values for
<b>%S</b>
extends from 0 to 61 seconds to accommodate the occasional leap second
or double leap second.
<p>
Although certain of the field descriptors 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 capitalisation
if the output is going to be used at the beginning of a sentence.
<p>
The date string formatting capabilities are intended for use in
Gregorian style calendars, possibly with a different starting
year (or years).
The
<b>%x</b>
and
<b>%c</b>
field descriptors, however, are
intended for local representation;
these may be based on a
different, non-Gregorian calendar.
<p>
The
<b>%C</b>
field descriptor was introduced to allow a fallback for the
<b>%EC</b>
(alternative year format base year);
it can be viewed as
the base of the current subdivision in the Gregorian calendar.
A century is not calculated as an ordinal number;
this Guide was published in century 19, not the twentieth.
Both the
<b>%Ey</b>
and
<b>%y</b>
can then be viewed as the offset from
<b>%EC</b>
and
<b>%C</b>,
respectively.
<p>
The
E
and
O
modifiers modify the traditional field descriptors,
so that they can always be used, even if the implementation (or
the current locale) does not support the modifier.
<p>
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-dependent extension
capable of supporting other calendar systems, especially in
combination with the
O
modifier.
<p>
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.
<p>
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
<b>%d</b>,
<b>%e</b>,
<b>%H</b>,
<b>%I</b>,
<b>%m</b>,
<b>%S</b>,
<b>%U</b>,
<b>%w</b>,
<b>%W</b>
and
<b>%y</b>
field descriptors
always return the date and time field in Latin digits (that is, 0 to 9).
The
<b>%O</b>
modifier was introduced to support the use
for display purposes of non-Latin digits.
In the LC_TIME category
in
<i><a href="localedef.html">localedef</a></i>,
the optional
<b>alt_digits</b>
keyword is intended
for this purpose.
As an example, assume the following (partial)
<i><a href="localedef.html">localedef</a></i>
source:
<pre>
<code>
alt_digits    "";"I";"II";"III";"IV";"V";"VI";"VII";"VIII" \
              "IX";"X";"XI";"XII"
d_fmt         "%e.%Om.%Y"
</code>
</pre>
With the above date, the command:
<pre>
<code>
date "+%x"
</code>
</pre>
would yield 3.IX.1991.
With the same
<b>d_fmt</b>,
but without the
<b>alt_digits</b>,
the command would yield 3.9.1991.
</blockquote><h4><a name = "tag_001_014_355">&nbsp;</a>EXAMPLES</h4><blockquote>
<ol>
<p>
<li>
The following are input/output examples of
<i>date</i>
used at arbitrary times in the POSIX locale:
<pre>
<code>
<b>$</b> date
<b>Tue Jun 26 09:58:10 PDT 1990</b>
</code>
</pre>
<pre>
<code>
<b>$</b> date "+DATE: %m/%d/%y%nTIME: %H:%M:%S"
<b>DATE: 11/02/91
TIME: 13:36:16</b>
</code>
</pre>
<pre>
<code>
<b>$</b> date "+TIME: %r"
<b>TIME: 01:36:32 PM</b>
</code>
</pre>
<p>
<li>
Examples for Denmark, where the
default date and time format is
"%a %d %b %Y %T %Z":
<pre>
<code>
<b>$</b> LANG=da_DK.iso_8859-1 date
<b>ons 02 okt 1991 15:03:32 CET
</b></code>
</pre>
<pre>
<code>
<b>$</b> LANG=da_DK.iso_8859-1 date"+DATO:%Aden%e.%B%Y%nKLOKKEN:%H:%M:%S"
<b>DATO: onsdag den  2. oktober 1991
KLOKKEN: 15:03:56
</b></code>
</pre>
<p>
<li>
Examples for Germany, where the
default date and time format is
"%a %d.%h.%Y, %T %Z":
<pre>
<code>
<b>$</b> LANG=De_DE.88591 date
<b>Mi 02.Okt.1991, 15:01:21 MEZ
</b></code>
</pre>
<pre>
<code>
<b>$</b> LANG=De_DE.88591 date "+DATUM: %A, %d. %B %Y%nZEIT:  %H:%M:%S" 
<b>DATUM: Mittwoch, 02. Oktober 1991
ZEIT:  15:02:02
</b></code>
</pre>
<br>
<p>
<li>
Examples for France, where the
default date and time format is
"%a %d %h %Y %Z %T":
<pre>
<code>
<b>$</b> LANG=Fr_FR.88591 date
<b>Mer 02 oct 1991 MET 15:03:32
</b></code>
</pre>
<pre>
<code>
<b>$</b> LANG=Fr_FR.88591 date "+JOUR:  %A %d %B %Y%nHEURE: %H:%M:%S"
<b>JOUR:  Mercredi 02 octobre 1991
HEURE: 15:03:56
</b></code>
</pre>
<p>
</ol>
</blockquote><h4><a name = "tag_001_014_356">&nbsp;</a>FUTURE DIRECTIONS</h4><blockquote>
None.
</blockquote><h4><a name = "tag_001_014_357">&nbsp;</a>SEE ALSO</h4><blockquote>
The <b>XSH</b> specification description of
<i><a href="../xsh/ctime.html">ctime()</a></i>,
<i><a href="../xsh/printf.html">printf()</a></i>.
</blockquote><hr size=2 noshade>
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