DateTime::TimeZone - Time zone object base class and factory

  use DateTime;
  use DateTime::TimeZone

  my $tz = DateTime::TimeZone->new( name => 'America/Chicago' );

  my $dt = DateTime->now();
  my $offset = $tz->offset_for_datetime($dt);

This class is the base class for all time zone objects. A time zone is represented internally as a set of observances, each of which describes the offset from GMT for a given time period.

Note that without the CWDateTime.pm module, this module does not do much. It's primary interface is through a CWDateTime object, and most users will not need to directly use CWDateTime::TimeZone methods.

This class has the following methods: Given a valid time zone name, this method returns a new time zone blessed into the appropriate subclass. Subclasses are named for the given time zone, so that the time zone America/Chicago is the DateTime::TimeZone::America::Chicago class. If the name given is a link name in the Olson database, the object created may have a different name. For example, there is a link from the old EST5EDT name to America/New_York. There are also several special values that can be given as names. If the name parameter is floating, then a CWDateTime::TimeZone::Floating object is returned. A floating time zone does have any offset, and is always the same time. This is useful for calendaring applications, which may need to specify that a given event happens at the same local time, regardless of where it occurs. See RFC 2445 for more details. If the name parameter is UTC, then a CWDateTime::TimeZone::UTC object is returned. If the name is an offset string, it is converted to a number, and a CWDateTime::TimeZone::OffsetOnly object is returned.

The local time zone

If the name parameter is local, then the module attempts to determine the local time zone for the system.

First it checks CW$ENV for keys named TZ, SYS$TIMEZONE_RULE, SYS$TIMEZONE_NAME, UCX$TZ, or TCPIP$TZC (the last 4 are for VMS). If this is defined, and it is not the string local, then it is treated as any other valid name (including floating), and the constructor tries to create a time zone based on that name.

Next, it checks for the existence of a symlink at /etc/localtime. It follows this link to the real file and figures out what the file's name is. It then tries to turn this name into a valid time zone. For example, if this file is linked to /usr/share/zoneinfo/US/Central, it will end up trying US/Central, which will then be converted to America/Chicago internally.

Some systems just copy the relevant file to /etc/localtime instead of making a symlink. In this case, we look in /usr/share/zoneinfo for a file that has the same size and content as /etc/localtime to determine the local time zone.

Then it checks for a file called /etc/timezone or /etc/TIMEZONE. If one of these exists, it is read and it tries to create a time zone with the name contained in the file.

Finally, it checks for a file called /etc/sysconfig/clock. If this file exists, it looks for a line inside the file matching CW/^(?:TIME)?ZONE="([^"]+)"/. If this line exists, it tries the value as a time zone name.

If none of these methods work, it gives up and dies.

CWDateTime::TimeZone objects provide the following methods: Given a CWDateTime object, this method returns the offset in seconds for the given datetime. This takes into account historical time zone information, as well as Daylight Saving Time. The offset is determined by looking at the object's UTC Rata Die days and seconds. Given a CWDateTime object, this method returns the offset in seconds for the given datetime. Unlike the previous method, this method uses the local time's Rata Die days and seconds. This should only be done when the corresponding UTC time is not yet known, because local times can be ambiguous due to Daylight Saving Time rules.

* name

Returns the name of the time zone. If this value is passed to the CWnew() method, it is guaranteed to create the same object. Given a CWDateTime object, this method returns the short name for the current observance and rule this datetime is in. These are names like EST, GMT, etc. It is strongly recommended that you do not rely on these names for anything other than display. These names are not official, and many of them are simply the invention of the Olson database maintainers. Moreover, these names are not unique. For example, there is an EST at both -0500 and +1000/+1100.

* is_floating

Returns a boolean indicating whether or not this object represents a floating time zone, as defined by RFC 2445.

* is_utc

Indicates whether or not this object represents the UTC (GMT) time zone.

* is_olson

Returns true if the time zone is a named time zone from the Olson database.

* category

Returns the part of the time zone name before the first slash. For example, the America/Chicago time zone would return America.

This class provides one class method:

* is_valid_name ($name)

Given a string, this method returns a boolean value indicating whether or not the string is a valid time zone name. If you are using CWDateTime::TimeZone::Alias, any aliases you've created will be valid.

This module provides freeze and thaw hooks for CWStorable so that the huge data structures for Olson time zones are not actually stored in the serialized structure.

If you subclass CWDateTime::TimeZone, you will inherit its hooks, which may not work for your module, so please test the interaction of your module with Storable.

This class also contains several functions, none of which are exported. Calling these as class methods will also work.

* all_names

This returns a pre-sorted list of all the time zone names. This list does not include link names. In scalar context, it returns an array reference, while in list context it returns an array.

* categories

This returns a list of all time zone categories. In scalar context, it returns an array reference, while in list context it returns an array.

* links

This returns a hash of all time zone links, where the keys are the old, deprecated names, and the values are the new names. In scalar context, it returns a hash reference, while in list context it returns a hash. Given a valid category, this method returns a list of the names in that category, without the category portion. So the list for the America category would include the strings Chicago, Kentucky/Monticello, and New_York. In scalar context, it returns an array reference, while in list context it returns an array. Given an offset as a string, this returns the number of seconds represented by the offset as a positive or negative number. Returns CWundef if CW$offset is not in the range CW-99:59:59 to CW+99:59:59. The offset is expected to match either CW/^([\+\-])?(\d\d?):(\d\d)(?::(\d\d))?$/ or CW/^([\+\-])?(\d\d)(\d\d)(\d\d)?$/. If it doesn't match either of these, CWundef will be returned. This means that if you want to specify hours as a single digit, then each element of the offset must be separated by a colon (:). Given an offset as a number, this returns the offset as a string. Returns CWundef if CW$offset is not in the range CW-359999 to CW359999.

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=datetime%3A%3Atimezone or via email at bug-datetime-timezone@rt.cpan.org.

Dave Rolsky <autarch@urth.org>

This module was inspired by Jesse Vincent's work on Date::ICal::Timezone, and written with much help from the datetime@perl.org list.

Copyright (c) 2003 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.

datetime@perl.org mailing list

http://datetime.perl.org/

The tools directory of the DateTime::TimeZone distribution includes two scripts that may be of interest to some people. They are parse_olson and tests_from_zdump. Please run them with the --help flag to see what they can be used for.