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.

   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.

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 datetimeATperl.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-localATrt.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, <autarchATurth.org>.



perl v5.12.4                                               2011-06-20                                           Time::Local(3pm)