Sure, we could just use a String to represent a date, like "April 19, 1987". But Ruby has a built-in class that makes it much easier to work with dates: Date.
The Date class isn’t loaded into every Ruby program by default, so to use it we first need to say
require "date"
(Usually we omit the parentheses around the string argument to the require method.)
After require "date", we can create a new instance as usual with:
Date.new # => #<Date: -4712-01-01 ((0j,0s,0n),+0s,2299161j)>
By default, the new date is January 1st, of the year -4712 BCE! Interesting1, but not very helpful.
You can also pass Date.new arguments to initialize with a specific year, month, and day:
Date.new(2001) #=> #<Date: 2001-01-01 ...>
Date.new(2001,2,3) #=> #<Date: 2001-02-03 ...>
Date.new(2001,2,-1) #=> #<Date: 2001-02-28 ...>
The Date.today method returns an object initialized to the current date.
Date.today # => #<Date: 2019-04-16 ((2458590j,0s,0n),+0s,2299161j)>
Call the year method on a Date object to return just the year of the date as an Integer.
t = Date.today # => #<Date: 2019-04-16 ((2458590j,0s,0n),+0s,2299161j)>
t.year # => 2019
Call the month method on a Date object to return just the month of the date as an Integer.
t = Date.today # => #<Date: 2019-04-16 ((2458590j,0s,0n),+0s,2299161j)>
t.month # => 4
Call the day method on a Date object to return just the day of the date as an Integer.
t = Date.today # => #<Date: 2019-04-16 ((2458590j,0s,0n),+0s,2299161j)>
t.day # => 16
The Date.parse() method accepts a String argument and tries to interpret it as a date, initializing a Date object.
Date.parse("2001-02-03") #=> #<Date: 2001-02-03 ...>
Date.parse("20010203") #=> #<Date: 2001-02-03 ...>
Date.parse("3rd Feb 2001") #=> #<Date: 2001-02-03 ...>
You can subtract two dates from one another, which will return the number of days between them. The return value class is a Rational, which can be converted to a regular Integer with .to_i:
number_of_days = Date.today - Date.parse("July 4, 1776")
=> (88674/1)
days.to_i
=> 88674
Returns true if the date is a Monday.
Returns true if the date is a Tuesday.
Returns true if the date is a Wednesday.
Returns true if the date is a Thursday.
Returns true if the date is a Friday.
Returns true if the date is a Saturday.
Returns true if the date is a Sunday.
Returns the day of week (0-6, Sunday is zero).
Date.new(2001,2,3).wday #=> 6
Ruby has a Time class as well, that shares most of its methods with the Date class.
Time.now.wday # => 6
Time.now.saturday? # => true
Time.now.day # => 3
The strftime method is used on a Date or Time object. It requires a String argument that will be used to format the Date or Time in a particular way.
Assuming today is Monday, September 7th 2020
Time.now.strftime("%A") # => "Monday"
Time.now.strftime("%B") # => "September"
Time.now.strftime("%b") # => "Sep"
Time.now.strftime("%a %e, %R %p") # => "Mon, 7 14:35 PM"
You should not try to memorize what these patterns mean. Tools like strftime.net and For a Good Strftime exist to help compose the formatting string argument.