Lua 5.1 doc says:
If format starts with '!', then the date is formatted in Coordinated
Universal Time.
If format is %c, !'s behavior seems correct
local date_1 = os.date("!%c")
local date_2 = os.date("%c")
print("utc date: "..date_1)
print("not utc date: "..date_2)
If format is *t, !'s behavior seems swapped
local time_1 = os.time(os.date("!*t"))
local time_2 = os.time(os.date("*t"))
print("should be utc time, but is not: "..time_1) -- this should be UTC, and is not
print("should not be utc time, but is: "..time_2) -- this should not be UTC, but is
Dates are tested with: http://www.epochconverter.com/
Why is that?
The table returned by os.date("!*t") and os.date("*t") is correct. I'm printing only the hour field. Note that they are consistent with %c format:
local date_1 = os.date("!%c")
local date_2 = os.date("%c")
print("utc date: "..date_1)
print("not utc date: "..date_2)
print("utc date hour: " .. os.date("!*t").hour)
print("not utc date hour: " .. os.date("*t").hour)
Output on my machine (China Standard Time, UTC+08:00):
utc date: 02/06/15 02:02:29
not utc date: 02/06/15 10:02:29
utc date hour: 2
not utc date hour: 10
However, os.time takes the table, assuming it's the local time, and returns the epoch. So, the local time is converted to the real epoch, but the utc time is not.
print(os.time{year=1970, month=1, day=1, hour=8})
outputs 0 on my machine.
Related
I got a bit problem when calculating the time difference from PM to AM or vice versa. For instance:
ref, _ := time.Parse("03:04pm", "11:59pm")
t, _ := time.Parse("03:04am", "12:00am")
fmt.Println(t.Sub(ref).Minutes()) // Got -719, my expectation is 1 (minutes)
Actually that's true, but I want to get the smallest difference.
The reason you got -719 is that you do not provide date information and in second time.Parse you have typo in template. Template has to contain pm
time.Parse("03:04pm", "11:59pm") // 0000-01-01 23:59:00 +0000 UTC
time.Parse("03:04am", "12:00am") // 0000-01-01 12:00:00 +0000 UTC
You need to provide day information and pm in template
time.Parse("02 03:04pm", "01 11:59pm") // 0000-01-01 23:59:00 +0000 UTC
time.Parse("02 03:04pm", "02 12:00am") // 0000-01-02 00:00:00 +0000 UTC
see https://stackoverflow.com/a/69338568/12301864
How should I interpret all aspects of the following timestamps? Where is the time based and how do timezones apply?
2015-11-15T14:45:28Z
2015-11-15T14:45:28.9694Z
2015-11-15T14:45:28.969412345Z
Below is my thoughts...
Date: 2015-11-15
???: T
Hours: 14
Minutes: 45
Seconds: 28 OR 28.9694 OR 28.969412345
???: Z
Most of your values are attributed correctly. The date portion (2015-11-15) is in the order YYYY-MM-DD, time in HH:MM:SS.ffff.
T indicates the start of the time portion of the date time.
Z indicates the time zone is UTC. Next to Z, you could have a format like Z+02:00, which indicates the time zone is UTC + 2 hours.
I am capturing the current time like so:
Time.now
My server runs on UTC. How can I convert the time to EST without using any Rails libraries? I am guessing some sort of offset but not sure how it works per say.
In plain Ruby you may use Time.zone_offset method:
require 'time'
t = Time.now # 2014-07-30 18:30:00 UTC
t + Time.zone_offset('EST') # 2014-07-30 13:30:00 UTC
The fbonetti's answer leads to the proper UTC to Eastern time conversion while accepted David Unric's answer would give wrong time for 8 months in 2017 (while DST is in effect).
Let's look at the following example:
First we'll need to figure out when DST starts/ends in 2017:
As we can see on March 12th, 2017 deep in the night (2:00am) they change time by adding +1 hour, so they "jump" from 1:59:59am up to 3:00:00am instantaneously! Which means there can not be 2:30am on March 12th, 2017.
Let's choose two UTC timestamps - one before and one after that switch, then we will try to convert those two timestamps from UTC back to Eastern.
First timestamp will be safely far enough from the switch moment:
require 'time'
t1 = Time.parse("2017-03-11 15:00:00 +0000")
=> 2017-03-11 15:00:00 +0000
t1_epoch_s = t1.to_i
=> 1489244400
Second timestamp is just +24 hours from the first one:
t2 = Time.parse("2017-03-12 15:00:00 +0000")
=> 2017-03-12 15:00:00 +0000
t2_epoch_s = t2.to_i
=> 1489330800
Now let us convert t1_epoch_s and t2_epoch_s to Eastern:
method-1: by adding Time.zone_offset('EST')
wrong, gives bad result: 10am for both days :(
and offset portion is shown as "+0000" which is also misleading and would refer to completely wrong point in time for people reading our output : ((
Time.at(t1_epoch_s) + Time.zone_offset('EST')
=> 2017-03-11 10:00:00 +0000
Time.at(t2_epoch_s) + Time.zone_offset('EST')
=> 2017-03-12 10:00:00 +0000
method-2: by changing timezone
Good!! Correctly yields 10am and 11am on next day!-)
ENV['TZ'] = 'America/New_York'
Time.at(t1_epoch_s)
=> 2017-03-11 10:00:00 -0500
Time.at(t2_epoch_s)
=> 2017-03-12 11:00:00 -0400
# resetting timezone back
ENV['TZ'] = nil
Basically manually adding Time.zone_offset('EST') is like adding constant and it will give right result for about 4 months (of 12 total) during the year, but then other time you'd have to manually add Time.zone_offset('EDT'), which is another constant. It pretty much same as "a broken clock is right twice a day": )) nasty!
And just for laughter let's see the "slow mo" how proper method handles the actual +1 hour magic jump in time:
ENV['TZ'] = "America/New_York"
Time.at(1489301999 + 0)
=> 2017-03-12 01:59:59 -0500
Time.at(1489301999 + 1)
=> 2017-03-12 03:00:00 -0400
ENV['TZ'] = nil
magic-magic!
In plain ruby, the timezone is determined by the 'TZ' environment variable. You could do something like this:
ENV['TZ'] = 'America/New_York' # set the TZ to Eastern Daylight Time
time = Time.now
time.zone
# => "EDT"
# do stuff
ENV['TZ'] = nil # reset the TZ back to UTC
If you don't mind using a gem,
require 'tzinfo'
tz = TZInfo::Timezone.get('US/Eastern')
Time.now.getlocal(tz.current_period.offset.utc_total_offset)
Credit: https://stackoverflow.com/a/42702906/2441263
I want to pull the latest UTC time from an array which contains various UTC time.
I could compare two time stamps in UTC as below:
#!/usr/bin/ruby
require "time"
a=Time.parse("2013-05-03 16:25:35 UTC")
b=Time.parse("2013-09-07 06:51:24 UTC")
if b < a
puts "latest time is #{a}"
else
puts "latest time is #{b}"
end
Output:
latest time is 2013-09-07 06:51:24 UTC
This way it is OK to compare only two time stamps. But my array contains more than 2 UTC time stamps and I need to chose the latest one. Here is the list of Array elements:
2013-04-30 12:13:20 UTC
2013-09-07 06:51:24 UTC
2013-05-03 16:25:35 UTC
2013-08-01 07:28:59 UTC
2013-04-09 13:42:36 UTC
2013-09-04 11:40:20 UTC
2013-07-01 06:47:52 UTC
2013-05-03 16:21:54 UTC
I want to chose the latest time from array which would be 2013-09-07 06:51:24 UTC
QUESTION:
How to compare all the array elements against each other on basis of UTC time ?
thanks.
Use Enumerable#max:
a = [ ... ] # Array of Time instances
latest = a.max
By default, max uses <=> to compare things and Time#<=> exists so this is probably the most straight forward way.
Your timestamps are (almost) in ISO 8601 format and those compare sensibly so you could leave them as Strings and apply max to an array of Strings as well.
Exact method is Array#sort or direct one Enumerable#max
require 'time'
time_ar = [ '2013-04-30 12:13:20 UTC',
'2013-09-07 06:51:24 UTC',
'2013-05-03 16:25:35 UTC',
'2013-08-01 07:28:59 UTC',
'2013-04-09 13:42:36 UTC',
'2013-09-04 11:40:20 UTC',
'2013-07-01 06:47:52 UTC',
'2013-05-03 16:21:54 UTC'
]
time_ar.map(&Time.method(:parse)).sort.last
# => 2013-09-07 06:51:24 UTC
time_ar.map(&Time.method(:parse)).max
# => 2013-09-07 06:51:24 UTC
I have an AWS server that runs daily cron jobs reporting on our user base. I want to ensure my report is run for the full day the previous day in MST. Currently I use this as the code for the data quering
Time.new(Time.now.year, Time.now.month, Time.now.day).yesterday.beginning_of_day.in_time_zone('MST)..Time.new(Time.now.year, Time.now.month, Time.now.day).yesterday.end_of_day.in_time_zone('MST)
I read it is bad practice to use Time.now as that is the system (UTC) time? I am wondering if what I am doing is a big no no or if there is a more efficient way?
thank you!
Mountain Standard Time is 7 hours behind UTC, so when you capture all the data points from the day of July 22rd in MST, you want the UTC times to be from 7/22 at 7:00AM UTC to 7/23 at 7:00AM UTC.
I don't think your code is correct because you are calling in_time_zone("MST") after beginning_of_day.
When you run this code on a server that is on UTC, the evaluated times are different:
>> Time.new.yesterday.beginning_of_day.in_time_zone('MST').utc
=> 2013-07-22 00:00:00 UTC
>> Time.new.in_time_zone("MST").yesterday.beginning_of_day.utc
=> 2013-07-22 07:00:00 UTC
Here is how you can determine the start and end times properly:
>> t = Time.new
=> 2013-07-23 19:45:10 +0000
>> start_time = t.in_time_zone("MST").yesterday.beginning_of_day
=> Mon, 22 Jul 2013 00:00:00 MST -07:00
>> end_time = t.in_time_zone("MST").yesterday.end_of_day
=> Mon, 22 Jul 2013 23:59:59 MST -07:00
When we convert the start and end times to UTC, we get the desired result.
>> start_time = t.in_time_zone("MST").yesterday.beginning_of_day.utc
=> 2013-07-22 07:00:00 UTC
>> end_time = t.in_time_zone("MST").yesterday.end_of_day.utc
=> 2013-07-23 06:59:59 UTC
I don't know what you are trying to do, but
Time.new(Time.now.year, Time.now.month, Time.now.day)
is definitely a terrible code fragment. For example, if the time lag between the execution time of Time.now.year and that of Time.now.month overlaps the moment of the change of the year, then the time object created with the main Time.new will be neither of the two moments. If you want to get the current time, just do
Time.new
or
Time.now
If you are trying to create a time range calculated out of a single time, then whatever your code should be, create time only once:
t = Time.now
and use that in the rest of your code:
t.some_method..t.some_other_method