As I understand, UTC means a time is given in timezone +00:00. But Ruby thinks different in Time#utc?. I've observed this in Ruby 2.5.1:
a = Time.new(2018,6,13, 9,0,0, '+00:00')
# => 2018-06-13 09:00:00 +0000
b = Time.utc(2018,6,13, 9,0,0)
# => 2018-06-13 09:00:00 UTC
a == b
# => true
a.utc?
# => false (WHY???)
b.utc?
# => true
IMHO, a.utc? should return true. Is there any explanation?
Addition: From the Ruby docs for Time#utc?
Returns true if time represents a time in UTC (GMT).
What exactly means "representing a time in UTC/GMT"? An offset of 0 is not enough, obviously.
Implementation-wise, Ruby's (i.e. MRI) internal time structure has a gmt field which specifies the time's type:
PACKED_STRUCT_UNALIGNED(struct time_object {
wideval_t timew; /* time_t value * TIME_SCALE. possibly Rational. */
struct vtm vtm;
uint8_t gmt:3; /* 0:localtime 1:utc 2:fixoff 3:init */
uint8_t tm_got:1;
});
The utc? method merely checks whether gmt is 1.
Therefore, a time instance in local time or a time instance with explicit offset will never be utc?, even if your system's timezone offset is UTC+0:
Time.local(2018) #=> 2018-01-01 00:00:00 +0000
Time.local(2018).utc? #=> false
Time.new(2018) #=> 2018-01-01 00:00:00 +0000
Time.new(2018).utc? #=> false
as opposed to a time instance created via utc: (note that the offset is shown as UTC)
Time.utc(2018) #=> 2018-01-01 00:00:00 UTC
Time.utc(2018).utc? #=> true
You could check the utc_offset instead:
t = Time.new(2018) #=> 2018-01-01 00:00:00 +0000
t.utc_offset #=> 0
t.utc_offset.zero? #=> true
Why do these two parse statements return different results?
time = "13:30:0"
DateTime.parse(time).to_time.utc
#=> 2013-10-13 13:30:00 UTC
Time.parse(time).utc
#=> 2013-10-13 11:30:00 UTC
There is no timezone information in the input String. DateTime.parse therefore assumes UTC. Time.parse assumes local time, and I guess you're in UTC+2.
>> time = "13:30:0"
=> "13:30:0"
>> DateTime.parse(time).to_s
=> "2013-10-13T13:30:00+00:00"
>> Time.parse(time).to_s
=> "2013-10-13 13:30:00 +0200"
I'm trying to get hours, minutes and seconds from current time and print it into format "hourminutesecond". For example "121103". But there isn't printed leading zero when I try to do it with next code
irb(main):021:0> ct = Time.now
=> 2012-11-06 12:11:03 +0100
irb(main):022:0> "#{ct.hour}#{ct.min}#{ct.sec}"
=> 12113
Output is "12113" but I want "121103".
Is there method or option for that. I can extract it with regex but just wondering if there is easier way to do it.
You should use time formatting:
ct = Time.now
ct # => Tue Nov 06 15:31:03 +0400 2012
ct.strftime('%H%M%S') # => "153103"
You should accept Sergio's answer as that's the correct way to deal with date/time objects.
However if you must do it using String class you can use rjust method to add a leading zero.
"#{ct.hour}#{ct.min}#{ct.sec}" # 12113
"#{ct.hour}#{ct.min}#{String(ct.sec).rjust(2,"0")}" # 121103
I have a Time object and would like to find the next/previous month. Adding subtracting days does not work as the days per month vary.
time = Time.parse('21-12-2008 10:51 UTC')
next_month = time + 31 * 24 * 60 * 60
Incrementing the month also falls down as one would have to take care of the rolling
time = Time.parse('21-12-2008 10:51 UTC')
next_month = Time.utc(time.year, time.month+1)
time = Time.parse('01-12-2008 10:51 UTC')
previous_month = Time.utc(time.year, time.month-1)
The only thing I found working was
time = Time.parse('21-12-2008 10:51 UTC')
d = Date.new(time.year, time.month, time.day)
d >>= 1
next_month = Time.utc(d.year, d.month, d.day, time.hour, time.min, time.sec, time.usec)
Is there a more elegant way of doing this that I am not seeing?
How would you do it?
Ruby on Rails
Note: This only works in Rails (Thanks Steve!) but I'm keeping it here in case others are using Rails and wish to use these more intuitive methods.
Super simple - thank you Ruby on Rails!
Time.now + 1.month
Time.now - 1.month
Or, another option if it's in relation to the current time (Rails 3+ only).
1.month.from_now
1.month.ago
Personally I prefer using:
Time.now.beginning_of_month - 1.day # previous month
Time.now.end_of_month + 1.day # next month
It always works and is independent from the number of days in a month.
Find more info in this API doc
you can use standard class DateTime
require 'date'
dt = Time.new().to_datetime
=> #<DateTime: 2010-04-23T22:31:39+03:00 (424277622199937/172800000,1/8,2299161)>
dt2 = dt >> 1
=> #<DateTime: 2010-05-23T22:31:39+03:00 (424282806199937/172800000,1/8,2299161)>
t = dt2.to_time
=> 2010-05-23 22:31:39 +0200
There are no built-in methods on Time to do what you want in Ruby. I suggest you write methods to do this work in a module and extend the Time class to make their use simple in the rest of your code.
You can use DateTime, but the methods (<< and >>) are not named in a way that makes their purpose obvious to someone that hasn't used them before.
If you do not want to load and rely on additional libraries you can use something like:
module MonthRotator
def current_month
self.month
end
def month_away
new_month, new_year = current_month == 12 ? [1, year+1] : [(current_month + 1), year]
Time.local(new_year, new_month, day, hour, sec)
end
def month_ago
new_month, new_year = current_month == 1 ? [12, year-1] : [(current_month - 1), year]
Time.local(new_year, new_month, day, hour, sec)
end
end
class Time
include MonthRotator
end
require 'minitest/autorun'
class MonthRotatorTest < MiniTest::Unit::TestCase
describe "A month rotator Time extension" do
it 'should return a next month' do
next_month_date = Time.local(2010, 12).month_away
assert_equal next_month_date.month, 1
assert_equal next_month_date.year, 2011
end
it 'should return previous month' do
previous_month_date = Time.local(2011, 1).month_ago
assert_equal previous_month_date.month, 12
assert_equal previous_month_date.year, 2010
end
end
end
below it works
previous month:
Time.now.months_since(-1)
next month:
Time.now.months_since(1)
I just want to add my plain ruby solution for completeness
replace the format in strftime to desired output
DateTime.now.prev_month.strftime("%Y-%m-%d")
DateTime.now.next_month.strftime("%Y-%m-%d")
You can get the previous month info by this code
require 'time'
time = Time.parse('2021-09-29 12:31 UTC')
time.prev_month.strftime("%b %Y")
You can try convert to datetime.
Time gives you current date, and DateTime allows you to operate with.
Look at this:
irb(main):041:0> Time.new.strftime("%d/%m/%Y")
=> "21/05/2015"
irb(main):040:0> Time.new.to_datetime.prev_month.strftime("%d/%m/%Y")
=> "21/04/2015"
Here is a solution on plain ruby without RoR, works on old ruby versions.
t=Time.local(2000,"jan",1,20,15,1,0);
curmon=t.mon;
prevmon=(Time.local(t.year,t.mon,1,0,0,0,0)-1).mon ;
puts "#{curmon} #{prevmon}"
Some of the solutions assume rails. But, in pure ruby you can do the following
require 'date'
d = Date.now
last_month = d<<1
last_month.strftime("%Y-%m-%d")
Im using the ActiveSupport::TimeZone for this example, but just in case you are using Rails or ActiveSupport it might come in handy.
If you want the previous month you can substract 1 month
time = Time.zone.parse('21-12-2008 10:51 UTC')
time.ago(1.month)
$ irb
irb(main):001:0> time = Time.now
=> 2016-11-21 10:16:31 -0800
irb(main):002:0> year = time.year
=> 2016
irb(main):003:0> month = time.month
=> 11
irb(main):004:0> last_month = month - 1
=> 10
irb(main):005:0> puts time
2016-11-21 10:16:31 -0800
=> nil
irb(main):006:0> puts year
2016
=> nil
irb(main):007:0> puts month
11
=> nil
irb(main):008:0> puts last_month
10
=> nil
If I have d = DateTime.now, how do I convert 'd' into UTC (with the appropriate date)?
DateTime.now.new_offset(0)
will work in standard Ruby (i.e. without ActiveSupport).
d = DateTime.now.utc
Oops!
That seems to work in Rails, but not vanilla Ruby (and of course that is what the question is asking)
d = Time.now.utc
Does work however.
Is there any reason you need to use DateTime and not Time? Time should include everything you need:
irb(main):016:0> Time.now
=> Thu Apr 16 12:40:44 +0100 2009
Unfortunately, the DateTime class doesn't have the convenience methods available in the Time class to do this. You can convert any DateTime object into UTC like this:
d = DateTime.now
d.new_offset(Rational(0, 24))
You can switch back from UTC to localtime using:
d.new_offset(DateTime.now.offset)
where d is a DateTime object in UTC time. If you'd like these as convenience methods, then you can create them like this:
class DateTime
def localtime
new_offset(DateTime.now.offset)
end
def utc
new_offset(Rational(0, 24))
end
end
You can see this in action in the following irb session:
d = DateTime.now.new_offset(Rational(-4, 24))
=> #<DateTime: 106105391484260677/43200000000,-1/6,2299161>
1.8.7 :185 > d.to_s
=> "2012-08-03T15:42:48-04:00"
1.8.7 :186 > d.localtime.to_s
=> "2012-08-03T12:42:48-07:00"
1.8.7 :187 > d.utc.to_s
=> "2012-08-03T19:42:48+00:00"
As you can see above, the initial DateTime object has a -04:00 offset (Eastern Time). I'm in Pacific Time with a -07:00 offset. Calling localtime as described previously properly converts the DateTime object into local time. Calling utc on the object properly converts it to a UTC offset.
Try this, works in Ruby：
DateTime.now.to_time.utc
You can set an ENV if you want your Time.now and DateTime.now to respond in UTC time.
require 'date'
Time.now #=> 2015-11-30 11:37:14 -0800
DateTime.now.to_s #=> "2015-11-30T11:37:25-08:00"
ENV['TZ'] = 'UTC'
Time.now #=> 2015-11-30 19:37:38 +0000
DateTime.now.to_s #=> "2015-11-30T19:37:36+00:00"
In irb:
>>d = DateTime.now
=> #<DateTime: 11783702280454271/4800000000,5/12,2299161>
>> "#{d.hour.to_i - d.zone.to_i}:#{d.min}:#{d.sec}"
=> "11:16:41"
will convert the time to the utc. But as posted if it is just Time you can use:
Time.now.utc
and get it straight away.