TZInfo – Daylight-savings aware timezone support for Ruby

TZInfo uses the tz database (www.twinsun.com/tz/tz-link.htm) to provide daylight-savings aware transformations between times in different timezones. This is the same database as used for zoneinfo on Unix machines.

The tz database has been imported (using TZDataParser) and turned into a set of Ruby modules (which are packaged with this release).

Example usage

To convert a time in UTC to a local time in the America/New_York timezone, you can do the following:

require 'tzinfo'

tz = TZInfo::Timezone.get('America/New_York')
local = tz.utc_to_local(Time.utc(2005,8,29,15,35,0))

Note that the Time returned will look like it is UTC (Time.zone will return “UTC”). This is because it is not currently possible to change the offset of an individual Time instance.

To convert from a local time to UTC, the local_to_utc method can be used.

utc = tz.local_to_utc(local)

Note that the timezone information of the time you pass in is ignored. The following two lines will return the same result regardless of the local timezone:

tz.local_to_utc(Time.local(2006,6,26,1,0,0))
tz.local_to_utc(Time.utc(2006,6,26,1,0,0))

To get information about the rules in force at a particular UTC or local time, the Timezone.period_for_utc and Timezone.period_for_local methods can be used. Both of these methods return TimezonePeriod objects. The following gets the identifier for the period (in this case EDT).

period = tz.period_for_utc(DateTime.new(2005,8,29,15,35,0))
id = period.zone_identifier

In all the above examples, instances of Time can be used instead of DateTime. Timezone#utc_to_local and Timezone#local_to_utc both return the type they are passed.

You can get the current local time in a Timezone with the Timezone#now method:

now = tz.now

All methods in TZInfo that take a time can be used with either Time, DateTime or Integers (Time#to_i). The return type will be the same as the type passed in.

You can also access Timezones by Country (ISO 3166 country code). The following gets all the Timezone identifiers for the US:

us = TZInfo::Country.get('US')
timezones = us.zone_identifiers

The zone_info method of Country provides an additional description and location for each Timezone in the Country.

The above covers the most common uses of Timezone and Country. For more detail, see the API documentation for the individual classes.

Download

The latest version of TZInfo can be found at

• rubyforge.org/frs/?group_id=894

API documentation can be found at

• tzinfo.rubyforge.org/doc/

Installation

The preferred method of installing TZInfo is through the GEM file (RubyGems required):

% gem install tzinfo-x.y.z.gem

or to automatically download and install:

% gem install tzinfo --remote

License

TZInfo is released under the MIT license.

Support

Please post to the TZInfo Users mailing list (rubyforge.org/mailman/listinfo/tzinfo-users) if you require assistance or have any suggestions.

Alternatively, you can contact the author Philip Ross directly at phil.ross@gmail.com.