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:

       •   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.

       •   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).

       •   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(3perl)