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Time::Local(3)        User Contributed Perl Documentation       Time::Local(3)

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 AT 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 AT rt.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 AT urth.org>.

perl v5.16.3                      2012-07-20                    Time::Local(3)