In this article you will learn what time-related classes & methods are available in Ruby and how to use them so you can become a time wizard!
Let’s do this!
To manage time in Ruby you can use the
This class represents a date:
And a time:
This information is stored by the
Time class as the number of seconds since the Epoch, also known as Unix time.
There are a few ways to initialize a
Timeobject using an Unix timestamp & the
Time.now # 2018-10-19 15:43:20 +0200 Time.new(2018, 1, 1) # 2018-01-01 00:00:00 +0100 Time.at(15000000000) # 2017-07-14 04:40:00 +0200
You can ask a time object for any of its components.
You can ask what day, month or hour a time object is representing:
t = Time.now puts t.day puts t.month puts t.hour
In addition, you can also ask if this date corresponds to a certain day of the week.
For example: “Is this date a Sunday?”.
These are predicate methods, meaning that they will return either true or false.
t = Time.now puts t.monday? puts t.sunday? puts t.friday?
Give it a try!
Time object has a time zone associated with it.
You can check the current time zone for a
Time object using the
This will give you the time zone abbreviation.
If you want the time zone offset you can use the
utc_offset method. The output for this method is in seconds, but you can divide by 3600 to get it in hours.
t = Time.now t.zone # "CET" t.utc_offset / 3600 # 1
You can also get the current time in UTC:
The default string representation for the time & date given to you by the Ruby Time class might not be what you want.
There is a method you can use to get almost any format you need.
This method is
strftime, which basically means ‘format time’.
It works by passing in a string with format specifiers, these specifiers will be replaced by a value. If you have ever used the
printf method the idea is very similar to that.
Let’s see some examples:
time = Time.new time.strftime("%d/%m/%Y") # "05/12/2015" time.strftime("%k:%M") # "17:48" time.strftime("Today is %A") # "Today is Sunday" time.strftime("%d of %B, %Y") # "21 of December, 2015" time.strftime("Unix time is %s") # "Unix time is 1449336630"
As you can see, this method is very flexible. You can get the time without the date, or a nicely formatted date with the year, day & name of the current month.
You can find more info on the different formats available on the following links:
Sometimes you don’t want the current time, but a time in the future or the past.
You can do addition with time objects!
Remember that the internal representation for
Time is in seconds, so you can do this:
# Add ten seconds time = Time.new + 10
In this example you get a time object that is set 10 seconds from the current time.
Then you can check if that time has passed yet.
Time.new > time
If you want to get something like yesterday’s day then you will need to calculate how many seconds there are in a day.
# seconds * minutes * hours 60 * 60 * 24 # 86400
Now with this number we can sustract that from the current date:
Time.now - 86400
If you are using Rails then you can do this:
Time.now - 1.day
Date class has no concept of minutes, seconds or hours. This class stores everything internally in terms of days.
To use the
Date class you need to
You can get the current date using
Date.new is not an alias for
today, so keep that in mind.
Date.today # Current date Date.new # Returns a negative date
Date arithmetic is similar to the
Time class, the difference is that you add days instead of seconds.
Date.today + 1 # Adds one day
Date doesn’t know anything about hours, seconds or minutes, so only use this class if you don’t need these.
Date.parse method will try to parse any string that looks like a date.
It uses a simple heuristic algorithm that tries to detect the input format.
Sometimes this will give unwanted results.
Date.parse("10/10/2010") # -> 2010-10-10 Date.parse("September 3") # -> 2015-09-03 Date.parse("May I have a cup of coffee, please?") # -> 1 of May
If you need something more strict you can use the
iso8601 date has the following format:
ArgumentError exception will be raised on invalid input.
You can use the
Date.strptime method & a set of format specifiers to provide your own custom input format. These are the same specifiers that you can use for
Date.strptime("3 of September", "%d of %B") # 2015-09-03
You can parse time using the
In other words:
How to convert a string like ‘2018-01-01 00:00’ into a Time object!
Here’s an example:
require 'time' Time.parse("September 20 18:00")
If you want to provide the format of your input string you can use the
require 'time' Time.strptime("1 of December 2017", "%d of %B %Y")
The only difference between
Date.parse is the kind of object that you get back (
Date class has some constants that you may find useful.
For example, there is an array with the months of the year and another with the days of the week.
Months start at index 1 so you can get a direct
month number -> month name mapping.
The days start with Sunday, but you can use the
rotate method to have the week start on Monday.
Date::MONTHNAMES # (index 0 = nil) Date::DAYNAMES.rotate(1)
DateTime class is a subclass of
Date and it can store seconds in addition to dates.
require 'date' DateTime.superclass # Date DateTime.now # DateTime: 2018-10-15T16:06:39+02:00
DateTime can get the same job done, with the main difference being that
Time is implemented in
C, so it will be faster.
Comparison: Time: 2644596.6 i/s DateTime: 231634.8 i/s - 11.42x slower
If you have used Rails you are probably familiar with things like
These methods are not available in pure Ruby, they are added by the
ActiveSupport component of Rails.
Here you can find some examples, notice how these methods don’t return
Date objects, but a custom
1.hour.to_i # 3600 1.day # ActiveSupport::Duration 3.days.ago # ActiveSupport::TimeWithZone
You can do time math with these & get things like tomorrow’s date:
Time.now + 1.day
Other Rails-exclusive time methods:
date = Time.current date.change(hour: 20) date.at_beginning_of_day
And for formatting:
date = Date.today date.to_formatted_s(:short) # "16 Jul" date.to_formatted_s(:long) # "July 16, 2018"
In this article you learned about the Time & Date classes, how to parse & format time in Ruby, and how to use the ActiveSupport time extensions.
Thanks for reading!