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The Ruby Date class is used to represent dates in Ruby and it has no concept of time. So, for example, you could represent the day you were born using the date class, but not the specific time.
Links
Date Formatting Strings
Date (Year, Month, Day):
%Y - Year with century if provided, will pad result at least 4 digits.
-0001, 0000, 1995, 2009, 14292, etc.
%C - year / 100 (rounded down such as 20 in 2009)
%y - year % 100 (00..99)
%m - Month of the year, zero-padded (01..12)
%_m blank-padded ( 1..12)
%-m no-padded (1..12)
%B - The full month name (``January'')
%^B uppercased (``JANUARY'')
%b - The abbreviated month name (``Jan'')
%^b uppercased (``JAN'')
%h - Equivalent to %b
%d - Day of the month, zero-padded (01..31)
%-d no-padded (1..31)
%e - Day of the month, blank-padded ( 1..31)
%j - Day of the year (001..366)
Code Samples
Instantiate a new date object:
Date.new
Date.new(2015, 3, 1)
Parsing dates from strings:
Date.parse("March 1st, 2015")
Date.parse("It's 2015, everyone!")
We can also pass in our own format string to the strptime method:
Date.strptime("It's 2015, everyone!", "It's %Y, everyone!")
Dates can be manipulated with mathematical operators:
Date.today
Date.today + 1
Date.today - 1
Date.today << 1 (subtract month)
Date.today >> 1 (add month)
Format strings can be passed as well:
Date.today.strftime("%Y %m, %d")
Date.today.strftime("%m %d, %Y")
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There are a few different ways to represent dates and times in Ruby.
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The Ruby date class is used to represent dates in Ruby, and
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it has no concept of time.
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So for example,
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you could represent the day that you were born using the date class.
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But not a specific time of day.
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Let's go ahead and take a look at how the date class works now using WorkSpaces.
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Okay, now we're going to take a look at the date library
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as part of the Standard Library.
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Now you'll notice that there are three different classes in use here,
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Date, DateTime, and Time.
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In this video we're just going to be concentrating on the Date class.
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Now we're gonna use the Date class, unsurprisingly,
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when we're working with dates.
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And this is gonna be without a time component,
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just to represent a certain date that you would like to in your program.
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Now here are all of the different methods that are supported by the Date class.
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Now we're just going to take a look at a few of these, but let's go ahead and
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get right into a workspace.
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So here I am in a workspace, I'm gonna launch irb.
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Now, the first thing that we need to do since we're working with something from
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the standard library is require it.
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So we require date, and now we have this date class that we can work with.
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If we were to just instantiate a date and called date.new, let's see what happens.
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We get this new date, and the year is -4712,
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on January 1st.
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Now, we can also pass arguments to Date.new if we want to,
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and that's done in the year month day format.
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So we could do date.new, 2015, and then we'll say we want January 1st.
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And now we get a new date object that has been instantiated to 2015-01-01.
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If we go back to the documentation and
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check out new, we can see the arguments that are supported.
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By default the year starts out at -4712 and
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the month is January and the day is the 1st of the month.
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So we can play around with that and create dates pretty much anytime we want to.
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2014, 7, 4, and that will create a date in the past.
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Now, creating dates is one thing.
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It's also useful to parse dates.
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There's a method called parse that we can use that will take a string and
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return a date object.
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And if we look at parse, it says that parse is the given representation of
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a date and time and creates just a date object.
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So if we go back to our workspace and say Date.parse("July 4th,
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2014"), we get back a date object that's
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exactly what we would expect, July 4th, 2014.
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And you'll notice if we use Date.parse,
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we put in month, day, year,
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and it parsed it out as year, month, day.
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So that's something to keep in mind when you're using parse.
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So here's another example.
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If we wanted to do Date.parse("March 1st, 2015"), that works.
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But if we wanted to pull out something like just the year, and say,
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it's 2015 everyone, it will say that that's an invalid date.
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Now, fortunately the Date class gives us another method that we can use
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to parse more complicated dates.
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So for example, using what we had just a minute ago,
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if we wanted to parse out a different string, we can use the strptime method.
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So where Date.parse didn't give us what we
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were expecting, with 07/04/2014, that gave us something we weren't expecting.
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We could use this strptime method.
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We pass in the string as the first argument.
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And then the format string is the second argument.
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And we get back exactly what we were expecting.
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And we're not limited to exactly this kind of format.
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For example, we could do that other one where we tried
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to parse "It's 2015, everyone!".
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Invalid date, but if we tell this string that we're just looking for the year.
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And then if we actually spell that correctly and take out the exclamation
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point, this functions exactly as we would expect it to.
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Let me clear my screen here and show you a couple other methods.
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If you want to get today's date, we can call the method Date.today,
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and as of the date of this recording, that is correct.
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What's nice about dates is that we can do addition and subtraction on them.
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So if I instantiated a new date to be today's date,
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I could add 1 to it and it would give me tomorrow's date.
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Could also do date- 1, which would give me yesterday's date.
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Sadly, this does not work with multiplication.
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And we get undefined method star for the date.
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Now instead of adding one day we could also add or subtract months
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using two greater than symbols and the number one that will add a month
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to the date and then two less than symbols will subtract a month from the date.
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I'm going to clear my screen one more time and
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one other thing that we can do is format date.
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So if we say date.to_s gives it one format.
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But, using the strftime method, we can pass in another format string.
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And it will print it out, just a little bit differently.
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The format string I'm using right now is the year with four characters,
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the month, a comma, and the day.
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Now we can flip that around if we want.
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And it'll tell us the day in pretty much any order that we want to.
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If you're curious about the different possible format strings,
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check out the notes below the video and you can see where they're coming from.
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Try setting and manipulating dates on your own now using WorkSpaces.
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