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Asked: 2026-05-20T05:56:45+00:00

In Ruby 1.8.7, how to set the time zone of a time? In the

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In Ruby 1.8.7, how to set the time zone of a time?

In the following examples, my system time zone is PST (-8:00 hours from UTC)

Given a time (21 Feb 2011, 20:45), presume that the time is in EST:

#this interprets the time as system time zone, i.e. PST
Time.local(2011,02,21,20,45) 
  #=> Mon Feb 21 20:45:00 -0800 2011

#this **converts** the time into EST, which is wrong!
Time.local(2011,02,21,20,45).in_time_zone "Eastern Time (US & Canada)" 
  #=> Mon, 21 Feb 2011 23:45:00 EST -05:00

But, the output I want is:
Mon Feb 21 20:45:00 -0500 2011 (Note the -0500 (EST) as opposed to -0800 (PST) and the hour is same, i.e. 20, not 23)

UPDATE (see the better version of this below)

I managed to get this to work, but I don’t like it:

DateTime.new(2011,02,21,20,45).change :offset => -(300.0 / 1440.0)
  # => Mon, 21 Feb 2011 20:45:00 +0500

Where
  300 = 5 hrs x 60 minutes
  1440 = number of minutes in a day

or the "right" way:

DateTime.civil(2011,02,21,20,45,0,Rational(-5, 24))

Question: Now, is there a way to determine the accurate(i.e. catering for daylight saving time etc) UTC offset from Time.zone so that I can pass it to the change method?

Reference: DateTime::change method

UPDATE (better version)

Thanks to @ctcherry for all the help!

Determine the accurate time zone info from Time.zone:

DateTime.civil(2011,02,21,20,45,0,Rational((Time.zone.tzinfo.current_period.utc_offset / 3600), 24))
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1 Answer

  1. Editorial Team

    In ruby 1.8.7 it doesn’t appear to be very easy to do what are asking for according to the documentation:

    http://www.ruby-doc.org/core-1.8.7/classes/Time.html

    However in 1.9 it looks a lot easier by passing the timezone offset to the localtime() method on a Time object:

    http://www.ruby-doc.org/core/classes/Time.html#M000346

    UPDATE

    The offset for Time.zone is easy since its an object on its own: (This is in a Rails console)

    ruby-1.8.7-p248 :001 > Time.zone
 => #<ActiveSupport::TimeZone:0x103150190 @current_period=nil, @name="Central Time (US & Canada)", @tzinfo=#<TZInfo::TimezoneProxy: America/Chicago>, @utc_offset=nil> 
ruby-1.8.7-p248 :002 > Time.zone.utc_offset
 => -21600 
ruby-1.8.7-p248 :003 > Time.zone.formatted_offset
 => "-06:00"
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