NAME¶
DateTime::TimeZone::SystemV - System V and POSIX timezone strings
SYNOPSIS¶
use DateTime::TimeZone::SystemV;
$tz = DateTime::TimeZone::SystemV->new(
name => "US Eastern",
recipe => "EST5EDT,M3.2.0,M11.1.0");
$tz = DateTime::TimeZone::SystemV->new(
"EST5EDT,M3.2.0,M11.1.0");
if($tz->is_floating) { ...
if($tz->is_utc) { ...
if($tz->is_olson) { ...
$category = $tz->category;
$tz_string = $tz->name;
if($tz->has_dst_changes) { ...
if($tz->is_dst_for_datetime($dt)) { ...
$offset = $tz->offset_for_datetime($dt);
$abbrev = $tz->short_name_for_datetime($dt);
$offset = $tz->offset_for_local_datetime($dt);
DESCRIPTION¶
An instance of this class represents a timezone that was specified by means of a
System V timezone recipe or an extended form of the same syntax (such as that
specified by POSIX). These can express a plain offset from Universal Time, or
a system of two offsets (standard and daylight saving time) switching on a
yearly cycle according to certain types of rule.
This class implements the DateTime::TimeZone interface, so that its instances
can be used with DateTime objects.
SYSTEM V TIMEZONE RECIPE SYSTEM¶
This module supports multiple versions of the timezone recipe syntax derived
from System V. Specifically, it supports the version specified by POSIX.1, and
the extension of the POSIX format that is used by version 3 of the
tzfile(5) file format.
A timezone may be specified that has a fixed offset by the syntax "
aaa ooo", or a timezone with DST by the syntax "
aaa
oooaaa[
ooo]
,rrr,rrr".
"
aaa" specifies an abbreviation by which an offset is known,
"
ooo" specifies the offset, and "
rrr" is a
rule for when DST starts or ends. For backward compatibility, the rules part
may also be omitted from a DST-using timezone, in which case some built-in
default rules are used; don't rely on those rules being useful.
An abbreviation must be a string of three or more characters from ASCII
alphanumerics, "
+", and "
-". If it contains
only ASCII alphabetic characters then the abbreviation specification "
aaa" may be simply the abbreviation. Otherwise "
aaa" must consist of the abbreviation wrapped in angle brackets
("
<...
>"). The angle bracket form is always
allowed. POSIX allows an implementation to set an upper limit on the length of
timezone abbreviations. The limit is known as "TZNAME_MAX", and is
required to be no less than 6 (characters/bytes). Abbreviations longer than 6
characters are therefore not portable. This class imposes no such limit.
An offset (from Universal Time), "
ooo", is given in hours, or
hours and minutes, or hours and minutes and seconds, with an optional
preceding sign. Hours, minutes, and seconds must be separated by colons. The
hours may be one or two digits, and the minutes and seconds must be two digits
each. The maximum magnitude permitted is 24:59:59. The sign in the
specification is the opposite of the sign of the actual offset. If no sign is
given then the default is "
+", meaning a timezone that is
behind UT (or equal to UT if the offset is zero). If no DST offset is
specified, it defaults to one hour ahead of the standard offset.
A DST-using timezone has one transition to DST and one transition to standard
time in each Gregorian year. The transitions may be in either order within the
year. If the transitions are in different orders from year to year then the
behaviour is undefined; don't rely on it remaining the same in future
versions. Likewise, the behaviour is generally undefined if transitions
coincide. However, in the
tzfile(5) variant, if the rules specify a
transition to DST at 00:00 standard time on 1 January and a transition to
standard time at 24:00 standard time on 31 December, which makes the
transitions coincide with those of adjacent years, then the timezone is
treated as observing DST all year.
A transition rule "
rrr" takes the form
"
ddd[
/ ttt]", where "
ddd" is
the rule giving the day on which the transition notionally takes place and
"
ttt" is the time of day at which the transition takes
place. (A time of day outside the usual 24-hour range can make the transition
actually take place on a different day.) The time may be given in hours, or
hours and minutes, or hours and minutes and seconds. Hours, minutes, and
seconds must be separated by colons. The minutes and seconds must be two
digits each. In the POSIX variant, the hours may be one or two digits, with no
preceding sign, and the time stated may range from 00:00:00 to 24:59:59
(almost an hour into the following day). In the
tzfile(5) variant, the
hours may be one to three digits, with optional preceding sign, and the time
stated may range from -167:59:59 to +167:59:59 (a span of a little over two
weeks). If the time is not stated then it defaults to 02:00:00. The time for
the transition to DST is interpreted according to the standard offset, and the
time for the transition to standard time is interpreted according to the DST
offset. (Thus normally the transition time is interpreted according to the
offset that prevailed immediately before the transition.)
A day rule "
ddd" may take three forms. Firstly,
"
Jnnn" means the month-day date that is the
nnnth day of a non-leap year. Thus "
J59" means the
February 28 and "
J60" means March 1 (even in a leap year).
February 29 cannot be specified this way.
Secondly, if "
ddd" is just a decimal number, it means the
(1+
ddd)th day of the year. February 29 counts in this case, and it is
not possible to specify December 31 of a leap year.
Thirdly, "
ddd" may have the form
"
Mm. w.d" means day
d of the
wth week of the
mth month. The day is given as a
single digit, with "
0" meaning Sunday and
"
6" meaning Saturday. The first week contains days 1 to 7 of
the month, the second week contains days 8 to 14, and so on. If "
w" is "
5" then the last week of the month
(containing its last seven days) is used, rather than the fifth week (which is
incomplete).
Examples:
- MUT-4
- Mauritius time, since 1907: 4 hours ahead of UT all year.
- EST5EDT,M3.2.0,M11.1.0
- US Eastern timezone with DST, from 2007 onwards. 5 hours behind UT in
winter and 4 hours behind in summer. Changes on the second Sunday in March
and the first Sunday in November, in each case at 02:00 local time.
- NST3:30NDT,M3.2.0/0:01,M11.1.0/0:01
- Newfoundland timezone with DST, from 2007 onwards. 3.5 hours behind UT in
winter and 2.5 hours behind in summer. Changes on the second Sunday in
March and the first Sunday in November, in each case at 00:01 local
time.
- GMT0BST,M3.5.0/1,M10.5.0
- UK civil time, from 1996 onwards. On UT during the winter, calling it
"GMT", and 1 hour ahead of UT during the summer, called
"BST". Changes on the last Sunday in March and the last Sunday
in October, in each case at 01:00 UT.
- EST-10EST,M10.5.0,M3.5.0/3
- Australian Eastern timezone, from 2007 onwards. 10 hours ahead of UT in
the southern winter (the middle of the calendar year), and 11 hours ahead
in the southern summer. Changes to DST on the last Sunday in October, and
back on the last Sunday in March, in each case at 02:00 standard time
(16:00 UT of the preceding day).
- EET-2EEST,M3.5.4/24,M9.3.6/145
- Palestinian civil time, from 2012 onwards. 2 hours ahead of UT in winter
and 3 hours ahead in summer. Changes at the end (24:00 local time) of the
last Thursday in March and 01:00 local time on the Friday following the
third Saturday in September (that is, the Friday falling between September
21 and September 27 inclusive). The extended time-of-day "145",
meaning 01:00 of the day six days after the nominal day, is only valid in
the tzfile(5) variant of the System V syntax. The time-of-day
"24" is not so restricted, being permitted by POSIX.
CONSTRUCTOR¶
- DateTime::TimeZone::SystemV->new(ATTR => VALUE, ...)
- Constructs and returns a DateTime-compatible timezone object that
implements the timezone described by the recipe given in the arguments.
The following attributes may be given:
- name
- Name for the timezone object. This will be returned by the
"name" method described below, and will be included in certain
error messages. If not given, then the recipe is used as the timezone
name.
- recipe
- The short textual timezone recipe, as described in "SYSTEM V TIMEZONE
RECIPE SYSTEM". Must be given.
- system
- Keyword identifying the particular variant of the recipe system according
to which the recipe is to be interpreted. It may be:
- posix (default)
- As specified by POSIX.1.
- tzfile3
- As specified by version 3 of the tzfile(5) file format.
- DateTime::TimeZone::SystemV->new(RECIPE)
- Simpler way to invoke the above constructor in the usual case. Only the
recipe is given; it will be interpreted according to POSIX system, and the
recipe will also be used as the timezone name.
METHODS¶
These methods are all part of the DateTime::TimeZone interface. See that class
for the general meaning of these methods; the documentation below only
comments on the specific behaviour of this class.
Identification¶
- $tz->is_floating
- Returns false.
- $tz->is_utc
- Returns false.
- $tz->is_olson
- Returns false.
- $tz->category
- Returns "undef", because the category concept doesn't properly
apply to these timezones.
- $tz->name
- Returns the timezone name. Usually this is the recipe that was supplied to
the constructor, but it can be overridden by the constructor's name
attribute.
Offsets¶
- $tz->has_dst_changes
- Returns a truth value indicating whether the timezone includes a DST
offset.
- $tz->is_dst_for_datetime(DT)
- DT must be a DateTime-compatible object (specifically, it must
implement the "utc_rd_values" method). Returns a truth value
indicating whether the timezone is on DST at the instant represented by
DT.
- $tz->offset_for_datetime(DT)
- DT must be a DateTime-compatible object (specifically, it must
implement the "utc_rd_values" method). Returns the offset from
UT that is in effect at the instant represented by DT, in
seconds.
- $tz->short_name_for_datetime(DT)
- DT must be a DateTime-compatible object (specifically, it must
implement the "utc_rd_values" method). Returns the time scale
abbreviation for the offset that is in effect at the instant represented
by DT.
- $tz->offset_for_local_datetime(DT)
- DT must be a DateTime-compatible object (specifically, it must
implement the "local_rd_values" method). Takes the local time
represented by DT (regardless of what absolute time it also
represents), and interprets that as a local time in the timezone of the
timezone object (not the timezone used in DT). Returns the offset
from UT that is in effect at that local time, in seconds.
If the local time given is ambiguous due to a nearby offset change, the
numerically lower offset (usually the standard one) is returned with no
warning of the situation. If the local time given does not exist due to a
nearby offset change, the method "die"s saying so.
SEE ALSO¶
DateTime, DateTime::TimeZone, POSIX.1
<
http://www.opengroup.org/onlinepubs/000095399/basedefs/xbd_chap08.html>,
tzfile(5)
AUTHOR¶
Andrew Main (Zefram) <zefram@fysh.org>
COPYRIGHT¶
Copyright (C) 2007, 2009, 2010, 2011, 2012, 2013 Andrew Main (Zefram)
<zefram@fysh.org>
LICENSE¶
This module is free software; you can redistribute it and/or modify it under the
same terms as Perl itself.