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Now it's time to look at dates.

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And anything that we're going to do with dates should

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probably start with the Get‑Date cmdlet.

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This is why I encourage you to read the help.

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You may have run Get‑Date and you just get the current datetime,

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but there are a number of parameters that you can use in order to

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format the way that the datetime is presented to you,

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and I'm going to go through some of these.

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So I can run Get‑Date and say format it using a .NET format of g,

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and this is lowercase.

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These format parameters are case sensitive.

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This gives me the date in this format,

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and the format will be appropriate to your culture.

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Because I am in North America, my format is month, day, year.

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If I do capital G, then I get that particular format.

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A lowercase u for the format will give me a UTC string.

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If you come from a UNIX background or Linux background,

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there is a uformat parameter, specify a UNIX‑type format,

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again, this too is case sensitive, so I'm telling PowerShell,

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get me the date formatted as year, underscore,

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and then the month.

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We can also create dates.

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So let's say that I have a string, maybe something I've created,

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or that I've read from a file, or pulled from somewhere.

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I can use Get‑Date to actually turn that into a datetime object.

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Don't try to fuss with the string to, say,

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pull out a year, or a month, or something,

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turn it into a datetime object,

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and then use the datetime things I'm going to show you.

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So let's do this, let's do Get‑Date and give it a year, a month, and a day.

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And here's another way that I can create a datetime object, so there's $b.

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Because I specified no time, it just defaults to 12:00 a.m.

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Now, this is just another type of object,

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so I'm going to look at all of the properties using

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Select‑Object and not necessarily using Get‑Member.

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Now that I see what these are,

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I could then access any of these properties in my PowerShell work.

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There are methods as well that we can use.

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So I'm just going to look at the methods of a DateTime object.

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Now, some of these are just things that are part of the .NET Framework,

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which we won't necessarily get into,

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but I will show you some ones that probably are of use to you.

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Any of these ones that say, To something,

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ShortDateString or LongDateString, those are things that you will want to use,

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or maybe something like this, hey, is $b,

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is it in daylight savings time?

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And gives me True or False and January 1st is not in daylight savings time.

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Or want to format this as a string, so I can format the date to a LongDateString.

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Maybe this is an easier way than using the format parameter,

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but these are methods that you probably are likely to use.

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There are a number of Add methods, AddDays, AddHours, AddMinutes, and so on.

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What day is it 45 days from now, or 45 days from $b?

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And I get a new datetime object.

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Or I want, say, I need what's the datetime in 1000 hours from now?

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Sometimes we want to go backwards and say, what time was it five months ago?

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My recommendation is, don't try to use the Subtract methods that you'll see,

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use the Add method and just add a negative number.

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So five months prior to $b is that, Sunday August 1st, 2021.

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This is the type of thing that you might need if you're working,

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for example, with user accounts in Active Directory.

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Any discussion of dates also needs to include timespans,

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how much time has occurred between two particular

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datetime objects or two datetime events.

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So I'm going to create a new datetime object,

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this is another way that you can do it,

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I'm going to create the variable $c and make it a datetime object.

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PowerShell will treat this string into a datetime value.

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Now, there's a cmdlet that we can use, New‑TimeSpan,

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and I'll let you read the help here.

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So I'm going to create a New‑TimeSpan variable and the Start will be $b,

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and the ending date will be $c.

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So what is that?

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All right, so there is the object.

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That is a TimeSpan object.

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You can see the Days, Hours, Minutes,

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as well as more granular approach with the TotalDays,

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TotalSeconds, and so on.

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This is another type of object, so if I wanted to,

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I could say, hey, I just want to know the Days property,

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161.

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The other way that you can create a TimeSpan is just simple subtraction.

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I can subtract $b from $c and get the same result.

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Now, TimeSpans, when we use them in our PowerShell work,

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typically will be displayed as a string,

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although you can also format it as a string,

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like this.

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I have some examples coming up where you'll see this again in action.

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So how about a practical example of using datetime values?

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I'm going to create a variable, and I'm going to list some file extensions.

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Now, what I want to do is use that,

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and I'm going to do Get‑ChildItem on my scripts folder,

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and I'm going to recursively search all files,

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but I only want these particular file types that I see in $in.

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I'm then going to group the results,

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and I'm going to group them on a custom property.

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So every file object has a CreationTime property, which is a datetime.

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I want to get the Year property of that datetime object,

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so we're grouping on a custom property,

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which will be the year that each of these files was created.

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I'm then going to select from that group object result,

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I'm going to create a property called Year,

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which will be the Name value from the Group‑Object,

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and then I'm going to create Size, so I'm going to take the group,

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and I'm going to pipe it to Measure‑Object and measure the length and the sum.

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Now, I want to point out here,

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here's another example where I'm leveraging the standard notation.

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Notice that the $_.Group piped Measure‑Object is all in parentheses.

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PowerShell is going to return that as an object.

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That object is a measurement object, right?

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We've seen that, that measurement object has a property called sum.

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This technique that I'm using here is a way of getting just the

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sum value all in line as I run the command,

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and then we'll do something similar,

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and this is another way of using Measure‑Object.

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I am going to take the Group, and remember,

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the Group property of the Group object is all the files

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that go to each of these file extensions,

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and I'm going to get the content of every file because these are

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all txt files and measure the number of lines,

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ignoring whitespace, and do the same thing.

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That whole command is in parentheses,

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which is going to give me a measurement object that has a Lines property,

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but all I want is the Lines value that will be used for the value for Lines.

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And then lastly, I'm going to format the results as a table,

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and I'm going to create a custom header for Format-Table called path,

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and I'm going to use my Scripts path as the value for that,

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and I'll AutoSize it to make it nice, and pretty,

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and easy to read.

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This will take a minute or so to run because I have to get all the files,

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group them, measure all the contents,

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and what's probably taking the longest amount of

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time is I have to take every file, read the contents,

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and then measure that.

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I'm creating a custom object that PowerShell will then pass on to Format-Table,

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which has to do its thing, and then finally,

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I will get the results written to the console here,

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and there we go.

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So now I have report that shows me the number of files for every year,

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how big they are, and the total number of lines.

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This is the type of thing that if I need this often or

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I want to share with someone else,

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I'm then going to build a PowerShell function around it.

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But if this doesn't work in the PowerShell console,

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you know, the function is not going to work,

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and I won't be able to do that. So doing this in the console, as I've done here, is always the first step.