NAME¶
Date::Manip::TZ - an interface to the time zone data
SYNOPSIS¶
use Date::Manip::TZ;
$tz = new Date::Manip::TZ;
Data for most (and hopefully all) time zones used around the world have been
gathered and is publicly available in the zoneinfo (or Olson) database.
This module uses the data from the zoneinfo database to perform various time
zone operations.
DESCRIPTION¶
Every time zone has some of the following characteristics:
- name
- Every time zone has a unique name. In the zoneinfo
database, these are something similar to:
America/New_York
- aliases
- Time zones may have (but are not required to have) one or
more aliases. Each alias is unique, and is not the same as any time zone
name. An alias can be used in exactly the same way as a name.
- periods
- Every time zone is broken up into periods. Each period
describes how a portion of time relates to GMT, and how it might be
expressed.
Each period includes the following information:
- start time, end time
- The period begin and ends at certain times. The times are
included both as an absolute GMT time, and as a wallclock time. The
wallclock start time is the time that will be on a clock just as the
period starts (i.e. after a time change). The wallclock end time is the
time on a clock immediately before the period ends.
- offset
- The entire period has an offset which is how much the
wallclock time differs from GMT.
- abbreviation
- When expressing the time period, an abbreviation (such as
EST) is typically used.
- daylight saving time flag
- Every period is categorized as a standard time or a
daylight saving time. The flag will be 1 if it is a daylight saving time,
or 0 if it is a standard time.
Date::Manip includes all of the data for all of the time zones from the zoneinfo
database. This data is available from:
ftp://ftp.iana.org/tz/
Additional data from other standards are also used.
The zoneinfo database is not necessary in order to use Date::Manip. Instead, all
of that data has been extracted and stored in a series of other modules which
are used to handle each time zone. In that way, Date::Manip has no dependency
on any other source of data.
The Date::Manip::Zones document contains detailed information on the data
available.
METHODS¶
In all methods, the following variables are used:
- $zone
- This is a string which contains a valid time zone name. For
example:
America/New_York
- $alias
- This is a strings which contains a valid time zone name, or
a valid time zone alias. For example:
America/New_York
US/Eastern
EST5EDT
- $abbrev
- This is a string which contains a valid time zone
abbreviation. For example:
EST
- $offset
- This is a time zone entered as an offset. An offset is
either a string of one of the formats:
+HH
+HHMM
+HHMMSS
+HH:MM
+HH:MM:SS
or it can be a list reference:
[HH,MM,SS]
If a list reference is used, the sign must be included with all values. So,
the offset "-05:30" would be the list reference:
[-5,-30,0]
- $dstflag
- This is always one of the values: std, stdonly, dst,
dstonly
It defaults to "std" if it is not present. When determining a time
zone, it is usually necessary to check a number of different time zone and
DST combinations.
If $dstflag is "std", it will check both standard and daylight
saving times, but will give preference to standard times. If $dstflag is
"stdonly", only standard times will be checked.
The "dst" flag will search both, but give preference to daylight
saving times. The "dstonly" values will only use daylight saving
times.
- $date
- A date is always a string containing a date in one of the
formats:
YYYYMMDDHH:MN:SS
YYYY-MM-DD-HH:MN:SS
YYYYMMDDHHMNSS
or a list reference:
[Y,M,D,H,MN,S]
- $isdst
- This is 0 if a date is in standard time, 1 if it is in
daylight saving time.
- $period
- A period is a list reference currently containing the
following items:
[ $dateUT, $dateLT, $offsetstr, $offset, $abbrev, $isdst,
$endUT, $endLT, $begUTs, $begLTs, $endUTs, $endLTs ]
$dateUT and $dateLT are the starting date of the period (i.e. the first
second in a period) in universal (GMT) time and local (wallclock) time.
$endUT and $endLT are the end date of the period (i.e. the last second in
a period) in universal and local time. These are all stored as list
references.
$offsetstr is the string representation of the offset
("+05:00:00") and $offset is the corresponding list reference
form ([5,0,0]).
$abbrev is the abbreviation that applies during this period, and $isdst is 0
or 1 if it is standard or daylight saving time.
When accessing the elements in a period, use ONLY positive indices. In other
words, to get $endUT, access it as $$period[6], NOT as $$period[-2], since
I am considering adding more information to the period description that
may speed up performance.
$begUTs is the string representation (YYYYMMDDHH:MN:SS) of $begUT. Similar
for $begLTs, $endUTs, and $endLTs.
The following methods are available:
- base
- config
- err
- new
- new_config
- Please refer to the Date::Manip::Obj documentation for
these methods.
- all_periods
-
@periods = $tz->all_periods($zone,$year);
This returns the description of all time zone periods that occur (in full or
in part) during the given year.
- convert
- convert_to_gmt
- convert_from_gmt
- convert_to_local
- convert_from_local
- These functions convert a date from one time zone to
another.
($err,$date,$offset,$isdst,$abbrev) =
$tz->convert($date,$from,$to [,$isdst]);
This converts a date in the time zone given by $from to the time zone given
by $to.
($err,$date,$offset,$isdst,$abbrev) =
$tz->convert_to_gmt($date [,$from] [,$isdst]);
This converts a date to GMT. If $from is given, it is the current time zone
of the date. If $from is omitted, it defaults to the local time zone.
The value of $isdst returned is always 0.
($err,$date,$offset,$isdst,$abbrev) =
$tz->convert_from_gmt($date [,$to]);
This converts a date from GMT to another time zone. If $to is given, the
date is converted to that time zone. Otherwise, it is converted to the
local time zone.
($err,$date,$offset,$isdst,$abbrev) =
$tz->convert_to_local($date [,$from] [,$isdst]);
($err,$date,$offset,$isdst,$abbrev) =
$tz->convert_from_local($date [,$to] [,$isdst]);
Similar to the convert_to_gmt and convert_from_gmt functions. If $from or
$to are omitted, they default to GMT.
If there is any ambiguity about whether $date is in DST or not (i.e. if it
is a date that is repeated during a time change due to the clock being
moved back), the $isdst option can be passed in as an argument (it should
be 0 or 1) to say which time to use. It is ignored in all cases where
$date can be determined without that information.
The $isdst value passed back is 1 if the converted date is in DST. The
$offset value passed back is a list reference containing the offset from
GMT. $abbrev passed back is the time zone abbreviation.
Error codes are:
0 No error
1 Invalid arguments
2 Invalid FROM zone
3 Invalid TO zone
4 Invalid date
- curr_zone
-
$tz->curr_zone();
This returns the system time zone. The system time zone is determined using
the methods described below in the DETERMINING THE SYSTEM TIME ZONE
section.
This is the time zone that is used by default unless the SetDate or
ForceDate config variable is set to a different zone.
$tz->curr_zone(1);
This clears the system time zone and re-determines it using the methods
described below.
The main reason to do this is if the curr_zone_methods method is used to
change how the time zone is determined.
- curr_zone_methods
-
$tz->curr_zone_methods(@methods);
This sets the list and order of methods to use in determining the local time
zone. The various methods available are listed below in the section
DETERMINING THE SYSTEM TIME ZONE.
Some methods may require one or more arguments. For example, the method
named "mainvar" takes an option that is the name of a variable.
The arguments must be included in the @methods list immediately after the
method name (so @methods is actually a mixture of method names and
arguments).
This method may not be used in any environment where taint checking is
enabled. If it is, it will issue a warning, but will NOT change the method
list.
- date_period
-
$period = $tz->date_period($date,$zone,$wallclock [,$isdst]);
This returns the period information for the given date. $date defaults to
GMT, but may be given as local (i.e. wallclock) time if $wallclock is
non-zero. The period information is described in the periods method below.
If a wallclock time is given, no period is returned if the wallclock time
doesn't ever appear (such as when a time change results in the clock
moving forward "skipping" a period of time). If the wallclock
time appears twice (i.e. when a time change results in the clock being set
back), the $isdst variable is used. The standard time is used unless
$isdst is non-zero. $isdst is ignored except in the case where there are
two possible periods.
- define_abbrev
-
($err,$val) = $tz->define_abbrev($abbrev,@zone);
When encountering an abbreviation, by default, all time zones which ever
include the abbreviation will be examine in the order given in the
Date::Manip::Zones manual.
Occasionally, it may be necessary to change the order. This is true if you
are parsing dates in a time zone which uses an abbreviation which is also
used in another time zone, and where the other time zone is given
preference. As an example, the abbreviation "ADT" will default
to the "Atlantic/Bermuda" time zone. If you are in the
"America/Halifax" time zone (which also uses that abbreviation),
you may want to change the order of time zones.
This will take an abbreviation (which must be a known abbreviation... there
is no means of defining a totally new abbreviation) and a list of zones.
This will set the list of zones that will be checked, and the order in
which they are checked, when a date is encountered with the given
abbreviation. It is not necessary that the list include every zone that
has ever used the abbreviation, but it may not include a zone that has
never used it.
If $abbrev is "reset", all abbreviations are reset to the standard
values. If @zone includes only the element 'reset', the default list for
$abbrev is restored.
The following error codes are returned:
0 No error
1 $abbrev is not a valid abbreviation in any time zone
2 A zone (returned as $val) is not a valid time zone
3 A zone (returned as $val) does not use the abbreviation
For more information about the different zones which may correspond to each
abbreviation, and the order in which they will be examined by default,
refer to the Date::Manip::Zones manual.
- define_alias
-
$err = $tz->define_alias($alias,$zone);
This will define a new alias (or override an existing alias). $zone must be
a valid zone or an error is returned.
For more information about the different aliases which are set by default,
refer to the Date::Manip::Zones manual.
If $alias is "reset", all aliases will be reset to the standard
values. If $zone is "reset", $alias will be reset to the
standard value.
- define_offset
-
($err,$val) = $tz->define_offset($offset, [$dstflag,] @zone);
This is similar to the define_abbrev method. When an offset is encountered,
all time zones which have ever included that offset are checked. This will
defined which time zones, and in what order, they should be checked.
The zones to both standard and daylight saving times which include the
offset (if $dstflag is "std" or "dst") or to only one
or the other.
If $offset is "reset", all lists are reset to the default values.
If @zone includes only the element 'reset', the default list and order is
restored for $offset ($dstflag must not be given).
The following error codes are returned:
0 No error
1 $offset is not a valid offset in any time zone
2 $offset is not a valid offset in the selected
time (if doing "dstonly" or "stdonly")
3 A zone (returned as $val) is not a valid time zone
4 A zone (returned as $val) does not use the offset
5 A zone (returned as $val) does not include the
offset in the selected time (if doing "dstonly"
or "stdonly")
9 Offset is not a valid offset
- periods
-
@periods = $tz->periods($zone,$year);
This returns the description of all time zone periods that begin during the
year given. The year is measured in universal (GMT) time.
If no time zone period starts in the given year, nothing is returned.
@periods = $tz->periods($zone,undef,$year);
This returns all periods that begin in any year from 0001 to $year.
@periods = $tz->periods($zone,$year0,$year1);
This returns all periods that begin in any year from $year0 to $year1.
- tzdata
- tzcode
-
$vers = $tz->tzdata();
$vers = $tz->tzcode();
These return the versions of the tzdata and tzcode packages used to generate
the modules.
- zone
-
$zone = $tz->zone(@args);
@zone = $tz->zone(@args);
This function will return a list of all zones, or the default zone, which
matches all of the supplied information. In scalar context, it will return
only the default zone. In list context, it will return all zones.
@args may include any of the following items, and the order is not
important.
A zone name or alias ($alias)
A zone abbreviation ($abbrev)
An offset ($offset)
A dstflag ($dstflag)
A date ($date)
It is NOT valid to include two of any of the items. Any time zone returned
will match all of the data supplied.
If an error occurs, undef is returned. If no zone matches, an empty string,
or an empty list is returned.
The order of the zones will be determined in the following way:
If $abbrev is given, the order of time zones will be determined by it (and
$dstflag). If $dstflag is "std", all zones which match $abbrev
in standard time are included, followed by all that match $abbrev in
saving time (but no duplication is allowed). The reverse is true if
$dstflag is "dst".
If $abbrev is not given, but $offset is, $offset (and $dstflag) will
determine the order given. If $dstflag is "std", all zones which
match $offset in standard time are included, followed by all that match
$offset in saving time (but no duplication is allowed). The reverse is
true if $dstflag is "dst".
If $date is given, only zones in which $date will appear in a zone that
matches all other information are given. $date is a wallclock time.
If no $zone, $abbrev, or $offset are entered, the local time zone may be
returned (unless $date is entered, and it doesn't exist in the local time
zone).
NOTE: there is one important thing to note with respect to $dstflag when you
are working with a timezone expressed as an offset and a date is passed
in. In this case, the default value of $dstflag is "dst" (NOT
"stdonly"), and you probably never want to pass in a value of
"std" (though passing in "stdonly" is okay).
For standard offsets (with no minute component), there is always a standard
timezone which matches that offset. For example, the timezone
"+0100" matches the timezone "Etc/GMT+01", so you will
never get a timezone in daylight saving time if $dstflag is
"std".
If you want to pass in a date of 2001-07-01-00:00:00 and an timezone of
"+0100" and you want to get a timezone that refers to that date
as a daylight saving time date, you must use the $dstflag of
"dst" (or "dstonly").
Because this is almost always the behavior desired, when a zone is passed in
as an offset, and a date is passed in, the default $dstflag is
"dst" instead of "std". In all other situations, the
default is still "std".
If the timezone is expressed as an abbreviation, this problem does not
occur.
Date::Manip makes use of three potentially different time zones when working
with a date.
The first time zone that may be used is the actual local time zone. This is the
time zone that the computer is actually running in.
The second time zone is the working time zone. Usually, you will want the
default time zone to be the local time zone, but occasionally, you may want
the default time zone to be different.
The third time zone is the actual time zone that was parsed, or set, for a date.
If a date contains no time zone information, it will default to the working
time zone.
The local time zone is determined using the methods described in the following
section. The preferred way is to locate the time zone in some system file, or
using some system command, or (in the case of a Windows operating system) to
look it up in the registry. If all of these methods fail, the local time zone
may be set using either the $::TZ or $ENV{TZ} variables. Please note that
these should ONLY be used to set the actual local time zone.
If you are running in one time zone, but you want to force dates to be specified
in an alternate time zone by default, you need to set the working time zone.
The working time zone defaults to the local time zone, but this can be changed
using either the SetDate or ForceDate config variables. Refer to the
Date::Manip::Config manual for more information.
Finally, when a date is actually parsed, if it contains any time zone
information, the date is stored in that time zone.
DETERMINING THE SYSTEM TIME ZONE¶
There are a large number of ways available for determining the time zone. Some
or all of them may be checked. A list of methods to use is provided by
default, and may be overridden by the curr_zone_methods function described
above. To override the default order and/or list of methods, just pass in a
list of method names (with arguments where necessary), and only those methods
will be done, and in the order given.
The following methods are available:
Method Argument(s) Procedure
====== =========== =========
main VAR The main variable named VAR is
checked. E.g. "main TZ" checks
the variable $::TZ .
env TYPE VAR The named environment variable
is checked and the type of
data stored there (TYPE can
be 'zone' or 'offset' which
is the number of seconds from
UTC).
file FILE Look in the given file for any
one of the following case
insensitive lines:
ZONE
tz = ZONE
zone = ZONE
timezone = ZONE
ZONE may be quoted (single or
double) and whitespace is
ignored. If the entire line
is a zone, it must be the first
non-blank non-comment line in
the file.
command COMMAND Runs a command which produces
a time zone as the output.
cmdfield COMMAND N Runs a command which produces
whitespace separated fields,
the Nth one containing the
time zone (fields are numbered
starting at 0, or from the
end starting at -1).
gmtoff Uses the current offset from
GMT to come up with a best guess.
registry Look up the value in the
Windows registry. This is only
available to hosts running a
Windows operating system.
Note that the "main" and "env" methods should only be used
to specify the actual time zone the system is running in. Use the SetDate and
ForceDate config variables to specify an alternate time zone that you want to
work in.
By default, the following methods are checked (in the order given) on Unix
systems:
main TZ
env zone TZ
file /etc/TIMEZONE
file /etc/timezone
file /etc/sysconfig/clock
file /etc/default/init
command "/bin/date +%Z"
command "/usr/bin/date +%Z"
command "/usr/local/bin/date +%Z"
cmdfield /bin/date -2
cmdfield /usr/bin/date -2
cmdfield /usr/local/bin/date -2
gmtoff
The default methods for Windows systems are:
main TZ
env zone TZ
registry
gmtoff
The default methods for VMS systems are:
main TZ
env zone TZ
env zone SYS$TIMEZONE_NAME
env zone UCX$TZ
env zone TCPIP$TZ
env zone MULTINET_TIMEZONE
env offset SYS$TIMEZONE_DIFFERENTIAL
gmtoff
The default methods for all other systems are:
main TZ
env zone TZ
gmtoff
If anyone wants better support for a specific OS, please contact me and we'll
coordinate adding it.
In all cases, the value returned from the method may be any of the following:
the full name of a time zone (e.g. America/New_York)
or an alias
an abbreviation (e.g. EDT) which will be used to
determine the zone if possible
an offset (+hh, +hhmn, +hh:mm, +hh:mm:ss) from GMT
The Date::Manip::Zones module contains information about the time zones and
aliases available, and what time zones contain the abbreviations.
DESIGN ISSUES¶
The design decisions made in writing this module may cause some questions (and
probably complaints). The time zone modules are all generated using scripts
(included in the Date::Manip distribution) which use the standard tzdata tools
to parse the tzdata files and store that information in perl modules.
I'd like to address some of them, to avoid answering some of the "why did
you do it that way" remarks. I do welcome discussion about these
decisions... but preferably after you understand why those decisions were made
so that that we have an informed basis to begin a discussion.
- Why not use existing zoneinfo files
- Some people will probably think that I should have written
an interface to the zoneinfo files which are distributed with most
operating systems. Although I considered doing that, I rejected the idea
for two reasons.
First, not all operating systems come with the zoneinfo databases in a user
accessible state (Microsoft for example). Even those that do include them
store the information in various formats and locations. In order to bypass
all that, I have included the data directly in these modules.
Second, as I was doing my initial investigations into this, I ran into a bug
in the Solaris zoneinfo tools (long since fixed I'm sure). I decided then
that I didn't want to depend on an implementation where I could not
control and fix the bugs.
- Why not use the native tzdata files
- Another decision people may question is that I parse the
tzdata files and store the data from them in a large number of perl
modules instead of creating an interface to the tzdata files directly.
This was done solely for the sake of speed. Date::Manip is already a slow
module. I didn't want to slow it down further by doing the complex parsing
required to interpret the tzdata files while manipulating dates. By
storing the data in these modules, there is little or no parsing done
while using Date::Manip modules. It costs a little disk space to store
this information... but very little of it is actually loaded at runtime
(time zone data is only loaded when the time zone is actually referred
to), so I feel it's a good tradeoff.
- Why store the information in so many files
- The data from the native tzdata files are parsed and stored
in two sets of modules. These include almost 500 Date::Manip::Offset::*
modules and almost 450 Date::Manip::TZ::* modules.
I note that on my linux box, /usr/share/zoneinfo (which contains data files
generated from the tzdata files) contains over 1700 files, so I'm not
doing anything "new" by breaking up the information into
separate files. And doing so has a huge impact on performance... it is not
necessary to load and/or manipulate data from time zones which are not in
use.
The minute I made the decision to distribute the timezone information
myself, as opposed to using the system version, it was a given that there
would be a lot of files.
These modules are loaded only when the time zone or offset is actually used,
so, unless dates from around the world are being parsed, only a very small
number of these modules will actually be loaded. In many applications,
only a single TZ module will be loaded. If parsing dates which have
timezone information stored as offsets, one or two Offset modules will
also be loaded.
- The disk space seems excessive
- Currently, the disk usage of the perl files is around 9 MB.
Total disk usage for /usr/share/zoneinfo on my computer is around 4 MB.
There are a couple of differences.
The primary difference is that the zoneinfo files are stored in a binary
(and hence, more compressed) version, where the perl modules have all the
data in pure text.
Since these are all automatically generated and used, it may be beneficial
to store the data in some packed binary format instead of the fully
expanded text form that is currently in use. This would decrease the disk
space usage, and might improve performance. However, the performance
improvement would happen only once per timezone, and would make for more
complicated code, so I'm not very interested in pursuing this.
Another aspect of the current modules is that they all include pod
documentation. Although not necessary, this allows users to easily see
what modules handle which time zones, and that's nice. It also allows me
to use pod_coverage tests for the module which is a nice check to make
sure that the documentation is accurate.
All told, I don't consider the disk usage excessive at all.
KNOWN PROBLEMS OR ISSUES¶
- Unable to determine Time Zone
- When using Date::Manip, when the module is initialized, it
must be able to determine the local time zone. If it fails to do so, an
error will occur:
Unable to determine Time Zone
and the script will exit.
In the past, this was the most common problem with using Date::Manip . With
the release of 6.00, this problem should be significantly less common. If
you do get this error, please refer to the section above DETERMINING THE
SYSTEM TIME ZONE for information about determining the local time zone. I
am also interested in hearing about this so that I can update the default
list of methods to be able to determine the local time zone better.
- Asia/Jerusalem time zone
- The Asia/Jerusalem time zone has a non-standard way of
specifying the start and end of Daylight Saving Time based on the Hebrew
calendar.
As a result, there is no way to specify a simple rule to define time zone
changes for all years in the future. As such, this module supports all
time zone changes currently specified in the zoneinfo database (which
currently goes to the year 2037) but does not attempt to correctly handle
zone changes beyond that date. As a result, Date::Manip should not be used
to parse dates in the Jerusalem time zone that are far enough in the
future that information is not included in the current version of the
zoneinfo database.
- LMT and zzz abbreviations
- Both the LMT and zzz abbreviations are used in the zoneinfo
databases. LMT is use for most time zones for the times before the
Gregorian calendar was adopted, and zzz is used for a few where the time
zone was created and no description of dates prior to that are supported.
Both LMT and zzz are basically ignored in parsing dates (because there is
no reasonable way to determine which zone they are referring to), and will
be treated as the local time zone regardless.
KNOWN BUGS¶
None known.
BUGS AND QUESTIONS¶
Please refer to the Date::Manip::Problems documentation for information on
submitting bug reports or questions to the author.
SEE ALSO¶
Date::Manip - main module documentation
LICENSE¶
This script is free software; you can redistribute it and/or modify it under the
same terms as Perl itself.
AUTHOR¶
Sullivan Beck (sbeck@cpan.org)