Time::Local - Efficiently compute time from local and GMT time
version 1.28
use Time::Local;
my $time = timelocal( $sec, $min, $hour, $mday, $mon, $year );
my $time = timegm( $sec, $min, $hour, $mday, $mon, $year );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 (i.e. 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().
timelocal_modern() and timegm_modern()When Time::Local was first written, it was a common practice to represent years as a two-digit value like 99 for 1999 or 1 for 2001. This caused all sorts of problems (google "Y2K problem" if you're very young) and developers eventually realized that this was a terrible idea.
The default exports of timelocal() and timegm() do a complicated calculation when given a year value less than 1000. This leads to surprising results in many cases. See "Year Value Interpretation" for details.
The time*_modern() subs do not do this year munging and simply take the year value as provided.
While it would be nice to make this the default behavior, that would almost certainly break a lot of code, so you must explicitly import these subs and use them instead of the default timelocal() and timegm().
You are strongly encouraged to use these subs in any new code which uses this module. It will almost certainly make your code's behavior less surprising.
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).
This does not apply to timelocal_modern or timegm_modern. Use those exports if you want to ensure consistent behavior as your code ages.
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.