path: root/upstream/debian-unstable/man3/Time::Piece.3perl

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.\" ========================================================================
.\"
.IX Title "Time::Piece 3perl"
.TH Time::Piece 3perl 2024-05-30 "perl v5.38.2" "Perl Programmers Reference Guide"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH NAME
Time::Piece \- Object Oriented time objects
.SH SYNOPSIS
.IX Header "SYNOPSIS"
.Vb 1
\&    use Time::Piece;
\&    
\&    my $t = localtime;
\&    print "Time is $t\en";
\&    print "Year is ", $t\->year, "\en";
.Ve
.SH DESCRIPTION
.IX Header "DESCRIPTION"
This module replaces the standard \f(CW\*(C`localtime\*(C'\fR and \f(CW\*(C`gmtime\*(C'\fR functions with
implementations that return objects. It does so in a backwards
compatible manner, so that using localtime/gmtime in the way documented
in perlfunc will still return what you expect.
.PP
The module actually implements most of an interface described by
Larry Wall on the perl5\-porters mailing list here:
<https://www.nntp.perl.org/group/perl.perl5.porters/2000/01/msg5283.html>
.SH USAGE
.IX Header "USAGE"
After importing this module, when you use localtime or gmtime in a scalar
context, rather than getting an ordinary scalar string representing the
date and time, you get a Time::Piece object, whose stringification happens
to produce the same effect as the localtime and gmtime functions. There is 
also a \fBnew()\fR constructor provided, which is the same as \fBlocaltime()\fR, except
when passed a Time::Piece object, in which case it's a copy constructor. The
following methods are available on the object:
.PP
.Vb 10
\&    $t\->sec                 # also available as $t\->second
\&    $t\->min                 # also available as $t\->minute
\&    $t\->hour                # 24 hour
\&    $t\->mday                # also available as $t\->day_of_month
\&    $t\->mon                 # 1 = January
\&    $t\->_mon                # 0 = January
\&    $t\->monname             # Feb
\&    $t\->month               # same as $t\->monname
\&    $t\->fullmonth           # February
\&    $t\->year                # based at 0 (year 0 AD is, of course 1 BC)
\&    $t\->_year               # year minus 1900
\&    $t\->yy                  # 2 digit year
\&    $t\->wday                # 1 = Sunday
\&    $t\->_wday               # 0 = Sunday
\&    $t\->day_of_week         # 0 = Sunday
\&    $t\->wdayname            # Tue
\&    $t\->day                 # same as wdayname
\&    $t\->fullday             # Tuesday
\&    $t\->yday                # also available as $t\->day_of_year, 0 = Jan 01
\&    $t\->isdst               # also available as $t\->daylight_savings
\&
\&    $t\->hms                 # 12:34:56
\&    $t\->hms(".")            # 12.34.56
\&    $t\->time                # same as $t\->hms
\&
\&    $t\->ymd                 # 2000\-02\-29
\&    $t\->date                # same as $t\->ymd
\&    $t\->mdy                 # 02\-29\-2000
\&    $t\->mdy("/")            # 02/29/2000
\&    $t\->dmy                 # 29\-02\-2000
\&    $t\->dmy(".")            # 29.02.2000
\&    $t\->datetime            # 2000\-02\-29T12:34:56 (ISO 8601)
\&    $t\->cdate               # Tue Feb 29 12:34:56 2000
\&    "$t"                    # same as $t\->cdate
\&
\&    $t\->epoch               # seconds since the epoch
\&    $t\->tzoffset            # timezone offset in a Time::Seconds object
\&
\&    $t\->julian_day          # number of days since Julian period began
\&    $t\->mjd                 # modified Julian date (JD\-2400000.5 days)
\&
\&    $t\->week                # week number (ISO 8601)
\&
\&    $t\->is_leap_year        # true if it\*(Aqs a leap year
\&    $t\->month_last_day      # 28\-31
\&
\&    $t\->time_separator($s)  # set the default separator (default ":")
\&    $t\->date_separator($s)  # set the default separator (default "\-")
\&    $t\->day_list(@days)     # set the default weekdays
\&    $t\->mon_list(@days)     # set the default months
\&
\&    $t\->strftime(FORMAT)    # same as POSIX::strftime (without the overhead
\&                            # of the full POSIX extension)
\&    $t\->strftime()          # "Tue, 29 Feb 2000 12:34:56 GMT"
\&    
\&    Time::Piece\->strptime(STRING, FORMAT)
\&                            # see strptime man page. Creates a new
\&                            # Time::Piece object
.Ve
.PP
Note that \f(CW\*(C`localtime\*(C'\fR and \f(CW\*(C`gmtime\*(C'\fR are not listed above.  If called as
methods on a Time::Piece object, they act as constructors, returning a new
Time::Piece object for the current time.  In other words: they're not useful as
methods.
.SS "Local Locales"
.IX Subsection "Local Locales"
Both wdayname (day) and monname (month) allow passing in a list to use
to index the name of the days against. This can be useful if you need
to implement some form of localisation without actually installing or
using locales. Note that this is a global override and will affect
all Time::Piece instances.
.PP
.Vb 1
\&  my @days = qw( Dimanche Lundi Merdi Mercredi Jeudi Vendredi Samedi );
\&
\&  my $french_day = localtime\->day(@days);
.Ve
.PP
These settings can be overridden globally too:
.PP
.Vb 1
\&  Time::Piece::day_list(@days);
.Ve
.PP
Or for months:
.PP
.Vb 1
\&  Time::Piece::mon_list(@months);
.Ve
.PP
And locally for months:
.PP
.Vb 1
\&  print localtime\->month(@months);
.Ve
.PP
Or to populate with your current system locale call:
    Time::Piece\->\fBuse_locale()\fR;
.SS "Date Calculations"
.IX Subsection "Date Calculations"
It's possible to use simple addition and subtraction of objects:
.PP
.Vb 1
\&    use Time::Seconds;
\&    
\&    my $seconds = $t1 \- $t2;
\&    $t1 += ONE_DAY; # add 1 day (constant from Time::Seconds)
.Ve
.PP
The following are valid ($t1 and \f(CW$t2\fR are Time::Piece objects):
.PP
.Vb 3
\&    $t1 \- $t2; # returns Time::Seconds object
\&    $t1 \- 42; # returns Time::Piece object
\&    $t1 + 533; # returns Time::Piece object
.Ve
.PP
However adding a Time::Piece object to another Time::Piece object
will cause a runtime error.
.PP
Note that the first of the above returns a Time::Seconds object, so
while examining the object will print the number of seconds (because
of the overloading), you can also get the number of minutes, hours,
days, weeks and years in that delta, using the Time::Seconds API.
.PP
In addition to adding seconds, there are two APIs for adding months and
years:
.PP
.Vb 2
\&    $t = $t\->add_months(6);
\&    $t = $t\->add_years(5);
.Ve
.PP
The months and years can be negative for subtractions. Note that there
is some "strange" behaviour when adding and subtracting months at the
ends of months. Generally when the resulting month is shorter than the
starting month then the number of overlap days is added. For example
subtracting a month from 2008\-03\-31 will not result in 2008\-02\-31 as this
is an impossible date. Instead you will get 2008\-03\-02. This appears to
be consistent with other date manipulation tools.
.SS Truncation
.IX Subsection "Truncation"
Calling the \f(CW\*(C`truncate\*(C'\fR method returns a copy of the object but with the
time truncated to the start of the supplied unit.
.PP
.Vb 1
\&    $t = $t\->truncate(to => \*(Aqday\*(Aq);
.Ve
.PP
This example will set the time to midnight on the same date which \f(CW$t\fR
had previously. Allowed values for the "to" parameter are: "year",
"quarter", "month", "day", "hour", "minute" and "second".
.SS "Date Comparisons"
.IX Subsection "Date Comparisons"
Date comparisons are also possible, using the full suite of "<", ">",
"<=", ">=", "<=>", "==" and "!=".
.SS "Date Parsing"
.IX Subsection "Date Parsing"
Time::Piece has a built-in \fBstrptime()\fR function (from FreeBSD), allowing
you incredibly flexible date parsing routines. For example:
.PP
.Vb 2
\&  my $t = Time::Piece\->strptime("Sunday 3rd Nov, 1943",
\&                                "%A %drd %b, %Y");
\&  
\&  print $t\->strftime("%a, %d %b %Y");
.Ve
.PP
Outputs:
.PP
.Vb 1
\&  Wed, 03 Nov 1943
.Ve
.PP
(see, it's even smart enough to fix my obvious date bug)
.PP
For more information see "man strptime", which should be on all unix
systems.
.PP
Alternatively look here: <http://www.unix.com/man\-page/FreeBSD/3/strftime/>
.PP
\fICAVEAT \fR\f(CI%A\fR\fI, \fR\f(CI%a\fR\fI, \fR\f(CI%B\fR\fI, \fR\f(CI%b\fR\fI, and friends\fR
.IX Subsection "CAVEAT %A, %a, %B, %b, and friends"
.PP
Time::Piece::strptime by default can only parse American English date names.
Meanwhile, Time::Piece\->\fBstrftime()\fR will return date names that use the current
configured system locale. This means dates returned by strftime might not be
able to be parsed by strptime. This is the default behavior and can be
overridden by calling Time::Piece\->\fBuse_locale()\fR. This builds a list of the
current locale's day and month names which strptime will use to parse with.
Note this is a global override and will affect all Time::Piece instances.
.PP
For instance with a German locale:
.PP
.Vb 1
\&    localtime\->day_list();
.Ve
.PP
Returns
.PP
.Vb 1
\&    ( \*(AqSun\*(Aq, \*(AqMon\*(Aq, \*(AqTue\*(Aq, \*(AqWed\*(Aq, \*(AqThu\*(Aq, \*(AqFri\*(Aq, \*(AqSat\*(Aq )
.Ve
.PP
While:
.PP
.Vb 2
\&    Time::Piece\->use_locale();
\&    localtime\->day_list();
.Ve
.PP
Returns
.PP
.Vb 1
\&    ( \*(AqSo\*(Aq, \*(AqMo\*(Aq, \*(AqDi\*(Aq, \*(AqMi\*(Aq, \*(AqDo\*(Aq, \*(AqFr\*(Aq, \*(AqSa\*(Aq )
.Ve
.SS YYYY\-MM\-DDThh:mm:ss
.IX Subsection "YYYY-MM-DDThh:mm:ss"
The ISO 8601 standard defines the date format to be YYYY-MM-DD, and
the time format to be hh:mm:ss (24 hour clock), and if combined, they
should be concatenated with date first and with a capital 'T' in front
of the time.
.SS "Week Number"
.IX Subsection "Week Number"
The \fIweek number\fR may be an unknown concept to some readers.  The ISO
8601 standard defines that weeks begin on a Monday and week 1 of the
year is the week that includes both January 4th and the first Thursday
of the year.  In other words, if the first Monday of January is the
2nd, 3rd, or 4th, the preceding days of the January are part of the
last week of the preceding year.  Week numbers range from 1 to 53.
.SS "Global Overriding"
.IX Subsection "Global Overriding"
Finally, it's possible to override localtime and gmtime everywhere, by
including the ':override' tag in the import list:
.PP
.Vb 1
\&    use Time::Piece \*(Aq:override\*(Aq;
.Ve
.SH CAVEATS
.IX Header "CAVEATS"
.ie n .SS "Setting $ENV{TZ} in Threads on Win32"
.el .SS "Setting \f(CW$ENV\fP{TZ} in Threads on Win32"
.IX Subsection "Setting $ENV{TZ} in Threads on Win32"
Note that when using perl in the default build configuration on Win32
(specifically, when perl is built with PERL_IMPLICIT_SYS), each perl
interpreter maintains its own copy of the environment and only the main
interpreter will update the process environment seen by strftime.
.PP
Therefore, if you make changes to \f(CW$ENV\fR{TZ} from inside a thread other than
the main thread then those changes will not be seen by strftime if you
subsequently call that with the \f(CW%Z\fR formatting code. You must change \f(CW$ENV\fR{TZ}
in the main thread to have the desired effect in this case (and you must
also call \fB_tzset()\fR in the main thread to register the environment change).
.PP
Furthermore, remember that this caveat also applies to \fBfork()\fR, which is
emulated by threads on Win32.
.SS "Use of epoch seconds"
.IX Subsection "Use of epoch seconds"
This module internally uses the epoch seconds system that is provided via
the perl \f(CWtime()\fR function and supported by \f(CWgmtime()\fR and \f(CWlocaltime()\fR.
.PP
If your perl does not support times larger than \f(CW\*(C`2^31\*(C'\fR seconds then this
module is likely to fail at processing dates beyond the year 2038. There are
moves afoot to fix that in perl. Alternatively use 64 bit perl. Or if none
of those are options, use the DateTime module which has support for years
well into the future and past.
.PP
Also, the internal representation of Time::Piece\->strftime deviates from the
standard POSIX implementation in that is uses the epoch (instead of separate
year, month, day parts). This change was added in version 1.30. If you must
have a more traditional strftime (which will normally never calculate day
light saving times correctly), you can pass the date parts from Time::Piece
into the strftime function provided by the POSIX module
(see strftime in POSIX ).
.SH AUTHOR
.IX Header "AUTHOR"
Matt Sergeant, matt@sergeant.org
Jarkko Hietaniemi, jhi@iki.fi (while creating Time::Piece for core perl)
.SH "COPYRIGHT AND LICENSE"
.IX Header "COPYRIGHT AND LICENSE"
Copyright 2001, Larry Wall.
.PP
This module is free software, you may distribute it under the same terms
as Perl.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
The excellent Calendar FAQ at <http://www.tondering.dk/claus/calendar.html>
.SH BUGS
.IX Header "BUGS"
The test harness leaves much to be desired. Patches welcome.