How do I get Ruby to parse time as if it were in a different time zone?

Question

I'm parsing something like this:

11/23/10 23:29:57

which has no time zone associated with it, but I know it's in the UTC time zone (while I'm not). How can I get Ruby to parse this as if it were in the UTC timezone?

maerics · Accepted Answer · 2010-11-24T01:29:06.913

46

You could just append the UTC timezone name to the string before parsing it:

require 'time'
s = "11/23/10 23:29:57"
Time.parse(s) # => Tue Nov 23 23:29:57 -0800 2010
s += " UTC"
Time.parse(s) # => Tue Nov 23 23:29:57 UTC 2010

edited Nov 24 '10 at 01:29

answered Nov 24 '10 at 01:08

maerics

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Doh! I actually tried that and misinterpreted the result. My bad. Thanks. – farhadf Nov 24 '10 at 01:59
5

Does not work in my case. `s="Fri Dec 3 17:05:41 2010 UTC"` will get parsed as local time and ignore the trailing `UTC` – Oktav Nov 11 '13 at 17:16
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This can't possibly be the best general case solution – Ramfjord Jul 12 '16 at 22:27
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Might work but it's not good engineering practice. – dwery Dec 05 '20 at 04:58

score 34 · Answer 2 · answered Sep 13 '19 at 02:45

34

credit from https://rubyinrails.com/2018/05/30/rails-parse-date-time-string-in-utc-zone/,

Time.find_zone("UTC").parse(datetime)
# => Wed, 30 May 2018 18:00:00 UTC +05:30

answered Sep 13 '19 at 02:45

new2cpp

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For the record this requires Rails (ActiveSupport at least) – Adrien Rey-Jarthon Nov 16 '21 at 10:13
There should really be a `TimeZone::UTC` constant so you don't have to find it via string name every time you want to use it! – JakeRobb Mar 15 '23 at 18:30

score 25 · Answer 3 · edited Nov 01 '13 at 21:52

25

If your using rails you can use the ActiveSupport::TimeZone helpers

current_timezone = Time.zone
Time.zone = "UTC"
Time.zone.parse("Tue Nov 23 23:29:57 2010") # => Tue, 23 Nov 2010 23:29:57 UTC +00:00
Time.zone = current_timezone

It is designed to have the timezone set at the beginning of the request based on user timezone.

Everything does need to have Time.zone on it, so Time.parse would still parse as the servers timezone.

http://api.rubyonrails.org/classes/ActiveSupport/TimeZone.html

Note: the time format you have above was no longer working, so I changed to a format that is supported.

edited Nov 01 '13 at 21:52

Mike Lyons

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answered Jul 25 '13 at 15:25

Pete Brumm

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If you don't want to change the whole Time.zone context, use ActiveSupport::TimeZone.new('UTC').parse – Jerph May 14 '15 at 14:57
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@Jerph, your answer is definitely the best – Alex Gusev May 24 '15 at 08:09
@jerph your approach is much better, and actually thread safe. – Pete Brumm Jan 19 '17 at 14:25
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With ActiveSupport::TimeZone you can even do it with a block (same as @jerph answer) : `Time.use_zone('UTC') { Time.zone.parse('Tue Nov 23 23:29:57 2010') }` – Mathiou May 04 '18 at 12:44

score 10 · Answer 4 · answered May 31 '18 at 09:23

10

If you are using ActiveSupport [from Rails, e.g], you can do this:

ActiveSupport::TimeZone["GMT"].parse("..... date string")

answered May 31 '18 at 09:23

Bret Weinraub

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score 9 · Answer 5 · answered Nov 14 '19 at 21:50

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Another pure Ruby (no Rails) solution if you don't want/need to load ActiveSupport.

require "time"

ENV['TZ'] = 'UTC'
Time.parse("2019/10/01 23:29:57")
#=> 2019-10-01 23:29:57 +0000

answered Nov 14 '19 at 21:50

Cimm

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This is the best answer thus far. Pure Ruby, no fRails! thank you! – Paul D. May 24 '20 at 20:55

score 5 · Answer 6 · answered Apr 12 '21 at 18:49

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Without rails dependencies: Time parses in local time but DateTime parses in UTC. Then you can transform it to a Time class if that's what you want:

require 'date'

DateTime.parse(string_to_parse).to_time

answered Apr 12 '21 at 18:49

jBilbo

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score 4 · Answer 7 · answered Aug 06 '15 at 12:49

4

An aliter to @Pete Brumm's answer without Time.zone set/unset

Time.zone.parse("Tue Nov 23 23:29:57 2010") + Time.zone.utc_offset

answered Aug 06 '15 at 12:49

Vignesh Jayavel

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How do I get Ruby to parse time as if it were in a different time zone?

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