Ruby DateTime Examples: require date

Use the DateTime class. Compute and manipulate dates and times.

DateTime. A million years pass. Still the ant is enclosed in amber. Nothing affects it. Outside the world changes and time continues its march forward.

In Ruby consider the DateTime class. It fetches the current date and relative dates. We use operators to adjust days and months. We can even check for leap years.

An example. This program gets the current date with DateTime.now. It also shows how to access the month, day and year parts of the DateTime.
Note: When this program was run, it was the last day of March. The output shows the correct values.
Month: This returns the numeric form of the month. So January will be equal to 1. And December will be equal to 12.
Day: This returns the numeric day integer. The first day of the month is 1. The last day depends on the month in question.
Year: The year is also stored in integer representation. It contains the full year number, not a shortened form.
Ruby program that uses DateTime.now require "date" # Get current date. current = DateTime.now # Print current month, day and year. print "Month: ", current.month, "\n" print " Day: ", current.day, "\n" print " Year: ", current.year, "\n" Output Month: 2 Day: 21 Year: 2017

Add, subtract. We can add or subtract an integer from a Date. Subtracting one yields the previous day, and adding one moves to the next day. In this way, we compute yesterday and tomorrow.
Note: Only integers are supported here. If you try adding or subtracting a floating-point number, the fractional part is ignored.
Ruby program that adds, subtracts days require "date" # First day of 2014. d = Date.new(2014, 1, 1) # Subtract one day to get the last day of 2013. subtract = d - 1 # Add one day to get the next day. add = d + 1 # Display values. puts subtract puts d puts add Output 2013-12-31 2014-01-01 2014-01-02

Gm, local. We create arbitrary times with the Time.gm and Time.local methods. Time.gm returns a UTC time. Time.local returns a time adjusted for your local time zone.
Here: In this program, I pass the year, month, and day to these methods. These are the first three arguments.
Further: We can pass more arguments to Time.gm to increase the accuracy of your time. Here I pass 6.
Mktime: This has the same effect as local. If it is easier for you to remember mktime, then you can use it instead.
Ruby program that uses gm, local # Create a UTC time for the specified values. t = Time.gm(2013, "mar", 15) puts t # Create time with local time zone. t = Time.local(2010, "apr", 10) puts t # More arguments can be passed. t = Time.gm(2012, "jun", 30, 6, 30, 30, 50) puts t Output 2013-03-15 00:00:00 UTC 2010-04-10 00:00:00 -0700 2012-06-30 06:30:30 UTC

Leap. This method tells us if a year is a leap year or not. Leap years have an extra day. We must first create a Date object with the Date.new initialize method.
Note: For testing leap years, the day and month are not relevant. Just the year is needed.
Ruby program that uses leap method require "date" def days_in_year(year) d = Date.new(year, 1, 1) # See if the year is a leap year. if d.leap? return 366 else return 365 end end # Test years for leap status. 2000.upto(2010) do |year| puts year.to_s << " has " << days_in_year(year).to_s << " days" end Output 2000 has 366 days 2001 has 365 days 2002 has 365 days 2003 has 365 days 2004 has 366 days 2005 has 365 days 2006 has 365 days 2007 has 365 days 2008 has 366 days 2009 has 365 days 2010 has 365 days

Upto, downto. Dates have helpful iterators. In Ruby we often prefer iterators over loops. For upto, the initial date is incremented upwards, a day at a time. And downto decrements the day.
Block: With iterators we specify a block that has a variable in it. With dates, this variable represents an interim day.
Ruby program that uses upto, downto require "date" d1 = Date.new(2014, 10, 5) d2 = Date.new(2014, 10, 7) puts "upto" # Iterate from low to high date. d1.upto(d2) do |d| puts d end puts "downto" # Iterate from high to low date. d2.downto(d1) do |d| puts d end Output upto 2014-10-05 2014-10-06 2014-10-07 downto 2014-10-07 2014-10-06 2014-10-05

Step. This iterator is more flexible than upto or downto. We specify the "increment" or decrement value. So a step of 7 advances an entire week on each iteration.
End: Step terminates when the next value reached has gone past the target value.
Also: Negative steps are allowed. With a negative step we can go backwards in time.
Ruby program that uses step require "date" first = Date.new(2014, 10, 1) last = Date.new(2014, 11, 1) # Advance seven days each iteration (these are Wednesdays). first.step(last, 7) do |d| puts d end Output 2014-10-01 2014-10-08 2014-10-15 2014-10-22 2014-10-29

Next. The next and succ methods return the successive date—the "tomorrow" date. To me, the next() method is more clearly named. In this program, I specify the end date of October.
Here: These methods return the first day of November. Succ and next roll over from October to November.
Ruby program that uses next, succ require "date" d = Date.new(2014, 10, 31) # Get the next date with succ or next. d2 = d.succ puts d2 d2 = d.next puts d2 Output 2014-11-01 2014-11-01

Months. We use shift operators with two greater than (or less than) signs to add (or subtract) months. This changes the month in a date. The plus and minus are used for days.
Ruby program that adds, subtracts months require "date" d = Date.new(2015, 5, 1) # Add two months to the date. d2 = d >> 2 puts d2 # Subtract three months from the date. d3 = d << 3 puts d3 Output 2015-07-01 2015-02-01

Wday. This number indicates the "day of week" or weekday of a date. It returns the numbers 0 through 6, with 0 meaning Sunday and 6 meaning Saturday.
And: When we call the next method the wday increments, unless it rolls over to 0 again.
Ruby program that uses wday require "date" # This is a Sunday, so its number is 0. d = Date.new(2014, 10, 5) puts d.wday # Next day is a Monday (number 1). d = d.next puts d.wday # Tuesday (number 2). d = d.next puts d.wday # One week later is Tuesday again. d += 7 puts d.wday Output 0 1 2 2

With DateTime, we access many date functions. These would be hard to implement. It is typically best to reuse these library methods where possible.

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