time::y2038(3pm) [debian man page]
Time::y2038(3pm) User Contributed Perl Documentation Time::y2038(3pm) NAME
Time::y2038 - Versions of Perl's time functions which work beyond 2038 SYNOPSIS
use Time::y2038; print scalar gmtime 2**52; # Sat Dec 6 03:48:16 142715360 DESCRIPTION
On many computers, Perl's time functions will not work past the year 2038. This is a design fault in the underlying C libraries Perl uses. Time::y2038 provides replacements for those functions which will work accurately +/1 142 million years. This only imports the functions into your namespace. To replace it everywhere, see Time::y2038::Everywhere. Replaces the following functions: gmtime() See "gmtime" in perlfunc for details. localtime() See "localtime" in perlfunc for details. timegm() my $time = timegm($sec, $min, $hour, $month_day, $month, $year); The inverse of "gmtime()", takes a date and returns the coorsponding $time (number of seconds since Midnight, January 1st, 1970 GMT). All values are the same as "gmtime()" so $month is 0..11 (January is 0) and the $year is years since 1900 (2008 is 108). # June 4, 1906 03:02:01 GMT my $time = timegm(1, 2, 3, 4, 5, 6); timegm() can take two additional arguments which are always ignored. This lets you feed the results from gmtime() back into timegm() without having to strip the arguments off. The following is always true: timegm(gmtime($time)) == $time; timelocal() my $time = timelocal($sec, $min, $hour, $mday, $month, $year); my $time = timelocal($sec, $min, $hour, $mday, $month, $year, $wday, $yday, $isdst); Like "timegm()", but interprets the date in the current time zone. "timelocal()" will normally figure out if daylight savings time is in effect, but if $isdst is given this will override that check. This is mostly useful to resolve ambiguous times around "fall back" when the hour between 1am and 2am occurs twice. # Sun Nov 4 00:59:59 2007 print timelocal(59, 59, 0, 4, 10, 107); # 1194163199 # Sun Nov 4 01:00:00 2007 DST, one second later print timelocal(0, 0, 1, 4, 10, 107, undef, undef, 1); # 1194163200 # Sun Nov 4 01:00:00 2007 no DST, one hour later print timelocal(0, 0, 1, 4, 10, 107, undef, undef, 0); # 1194166800 $wday and $yday are ignored. They are only there for compatibility with the return value of "localtime()". LIMITATIONS
The safe range of times is +/ 2**52 (about 142 million years). Although the underlying time library can handle times from -2**63 to 2**63-1 (about +/- 292 billion years) Perl uses floating point numbers internally and so accuracy degrates after 2**52. BUGS &; FEEDBACK See http://rt.cpan.org/Dist/Display.html?Queue=Time-y2038 to report and view bugs. If you like the module, please drop the author an email. The latest version of this module can be found at http://y2038.googlecode.com/ and the repository is at http://y2038.googlecode.com/svn/trunk/ in perl/Time-y2038. You have to check out the whole repository because there are symlinks. AUTHOR
Michael G Schwern <schwern@pobox.com> LICENSE &; COPYRIGHT Copyright 2008-2010 Michael G Schwern This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself. See http://www.perl.com/perl/misc/Artistic.html SEE ALSO
Time::y2038::Everywhere overrides localtime() and gmtime() across the whole program. The y2038 project at http://y2038.googlecode.com/ <http://xkcd.com/376/> perl v5.14.2 2011-11-15 Time::y2038(3pm)
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Time::Local(3pm) Perl Programmers Reference Guide Time::Local(3pm) NAME
Time::Local - efficiently compute time from local and GMT time SYNOPSIS
$time = timelocal( $sec, $min, $hour, $mday, $mon, $year ); $time = timegm( $sec, $min, $hour, $mday, $mon, $year ); DESCRIPTION
This module provides functions that are the inverse of built-in perl functions "localtime()" and "gmtime()". They accept a date as a six- element array, and return the corresponding time(2) value in seconds since the system epoch (Midnight, January 1, 1970 GMT on Unix, for example). This value can be positive or negative, though POSIX only requires support for positive values, so dates before the system's epoch may not work on all operating systems. It is worth drawing particular attention to the expected ranges for the values provided. The value for the day of the month is the actual day (ie 1..31), while the month is the number of months since January (0..11). This is consistent with the values returned from "localtime()" and "gmtime()". FUNCTIONS
"timelocal()" and "timegm()" This module exports two functions by default, "timelocal()" and "timegm()". The "timelocal()" and "timegm()" functions perform range checking on the input $sec, $min, $hour, $mday, and $mon values by default. "timelocal_nocheck()" and "timegm_nocheck()" If you are working with data you know to be valid, you can speed your code up by using the "nocheck" variants, "timelocal_nocheck()" and "timegm_nocheck()". These variants must be explicitly imported. use Time::Local 'timelocal_nocheck'; # The 365th day of 1999 print scalar localtime timelocal_nocheck( 0, 0, 0, 365, 0, 99 ); If you supply data which is not valid (month 27, second 1,000) the results will be unpredictable (so don't do that). Year Value Interpretation Strictly speaking, the year should be specified in a form consistent with "localtime()", i.e. the offset from 1900. In order to make the interpretation of the year easier for humans, however, who are more accustomed to seeing years as two-digit or four-digit values, the following conventions are followed: o Years greater than 999 are interpreted as being the actual year, rather than the offset from 1900. Thus, 1964 would indicate the year Martin Luther King won the Nobel prize, not the year 3864. o Years in the range 100..999 are interpreted as offset from 1900, so that 112 indicates 2012. This rule also applies to years less than zero (but see note below regarding date range). o Years in the range 0..99 are interpreted as shorthand for years in the rolling "current century," defined as 50 years on either side of the current year. Thus, today, in 1999, 0 would refer to 2000, and 45 to 2045, but 55 would refer to 1955. Twenty years from now, 55 would instead refer to 2055. This is messy, but matches the way people currently think about two digit dates. Whenever possible, use an absolute four digit year instead. The scheme above allows interpretation of a wide range of dates, particularly if 4-digit years are used. Limits of time_t On perl versions older than 5.12.0, the range of dates that can be actually be handled depends on the size of "time_t" (usually a signed integer) on the given platform. Currently, this is 32 bits for most systems, yielding an approximate range from Dec 1901 to Jan 2038. Both "timelocal()" and "timegm()" croak if given dates outside the supported range. As of version 5.12.0, perl has stopped using the underlying time library of the operating system it's running on and has its own implementation of those routines with a safe range of at least +/ 2**52 (about 142 million years). Ambiguous Local Times (DST) Because of DST changes, there are many time zones where the same local time occurs for two different GMT times on the same day. For example, in the "Europe/Paris" time zone, the local time of 2001-10-28 02:30:00 can represent either 2001-10-28 00:30:00 GMT, or 2001-10-28 01:30:00 GMT. When given an ambiguous local time, the timelocal() function should always return the epoch for the earlier of the two possible GMT times. Non-Existent Local Times (DST) When a DST change causes a locale clock to skip one hour forward, there will be an hour's worth of local times that don't exist. Again, for the "Europe/Paris" time zone, the local clock jumped from 2001-03-25 01:59:59 to 2001-03-25 03:00:00. If the "timelocal()" function is given a non-existent local time, it will simply return an epoch value for the time one hour later. Negative Epoch Values On perl version 5.12.0 and newer, negative epoch values are fully supported. On older versions of perl, negative epoch ("time_t") values, which are not officially supported by the POSIX standards, are known not to work on some systems. These include MacOS (pre-OSX) and Win32. On systems which do support negative epoch values, this module should be able to cope with dates before the start of the epoch, down the minimum value of time_t for the system. IMPLEMENTATION
These routines are quite efficient and yet are always guaranteed to agree with "localtime()" and "gmtime()". We manage this by caching the start times of any months we've seen before. If we know the start time of the month, we can always calculate any time within the month. The start times are calculated using a mathematical formula. Unlike other algorithms that do multiple calls to "gmtime()". The "timelocal()" function is implemented using the same cache. We just assume that we're translating a GMT time, and then fudge it when we're done for the timezone and daylight savings arguments. Note that the timezone is evaluated for each date because countries occasionally change their official timezones. Assuming that "localtime()" corrects for these changes, this routine will also be correct. BUGS
The whole scheme for interpreting two-digit years can be considered a bug. SUPPORT
Support for this module is provided via the datetime@perl.org email list. See http://lists.perl.org/ for more details. Please submit bugs to the CPAN RT system at http://rt.cpan.org/NoAuth/ReportBug.html?Queue=Time-Local or via email at bug-time-local@rt.cpan.org. COPYRIGHT
Copyright (c) 1997-2003 Graham Barr, 2003-2007 David Rolsky. All rights reserved. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself. The full text of the license can be found in the LICENSE file included with this module. AUTHOR
This module is based on a Perl 4 library, timelocal.pl, that was included with Perl 4.036, and was most likely written by Tom Christiansen. The current version was written by Graham Barr. It is now being maintained separately from the Perl core by Dave Rolsky, <autarch@urth.org>. perl v5.18.2 2013-11-04 Time::Local(3pm)