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So let's hop back into PowerShell, go to a prompt,

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and let me demonstrate these filtering concepts and techniques.

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Alright, once again, let's turn to Get‑Vegetable,

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my command that we can use to demonstrate and illustrate these filtering ideas.

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If you've been jumping around and haven't seen this command before,

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it's part of a module called PS Teaching Tools,

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and I have a note in the download file that will explain how you can

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install the module so you can get this command.

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I'll go ahead and run it.

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And as we have seen before in the in this course,

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this gives me then a collection of vegetable objects.

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If I look at help for Get‑Vegetable,

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I can see that there are a few parameters that I can use to limit,

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or restrict, or filter, if you will,

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the information that that command is going to generate.

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So let's try this with the name parameter and just get,

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say, just radishes, and sure enough,

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that works just the way that I would expect it to.

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I can even refine this and say, you know what,

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show me all the vegetables where the name starts with r,

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and sure enough, it does.

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Now let's look at PowerShell commands.

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Let's look at Get‑Service.

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And as we can see,

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there are a number of parameters that looks like they'll help us

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limit or filter the services from the very beginning.

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So let's do Get‑Service, and let's do m*,

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find all the services that start with m.

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That's pretty good, pretty easy.

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There's another parameter just to kind of

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demonstrate how these things might work.

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There is an exclude parameter.

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So let's say, you know what, I want to get all the services that start with m,

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but I don't want the one to start with ms.

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So let's do get‑service m*, now, the name parameter is positional,

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that's why I didn't type it in, Exclude,

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though,

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I have to type the name and tell it to exclude any service that starts with ms,

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and now I get a simpler list.

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So that all works the way that I expect it to.

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Good examples of early filtering.

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I want to show you some early filtering with the file system and

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with Get‑ChildItem, or the dir alias. Because this is the stuff

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that you're going to see a lot, and it will confuse you,

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so let me take a few minutes to go through this.

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If I do directory of my scripts folder, say,

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show me all the ps1 files in scripts.

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So there we go, so that's all the files in the root of my scripts folder.

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When you look at help, you'll also see, oh, there's a filter parameter.

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That's kind of cool.

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Maybe that will be very helpful.

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Jeff was talking about filtering early.

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There's an option to filter.

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Cool, that seems to work as well.

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There's also, if you look at help,

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you'll see that Get‑ChildItem has an include parameter.

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So you might think, oh, I'll just try this.

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I'll do include *.ps1.

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I don't see anything.

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Well, that's because there's actually a little trick here with this,

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and that's why you have to read the help.

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Let me rerun the command.

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So we're going to include .ps1, and you know what,

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I'm going to also exclude that trial.ps1 that you see there.

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For the include and exclude, you actually also have to Recurse,

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and now that works.

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So whether you use the filter, the path,

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the name, the include, or exclude really all depends upon,

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not only what you're trying to do, but maybe where you're trying to do it.

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Let me give you another example here.

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PowerShell has other drives other than the file system, you know,

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things like the registry, and the functions,

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and aliases.

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So I'm going to just use the alias PSDrive.

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It's the same command, Get‑ChildItem, and you can use the dir alias,

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and I'm saying,

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look at the alias PSDrive and find me all the aliases that start with c,

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and I get an error message.

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And in fact, it makes it very clear, Get‑ChildItem cannot call that method.

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The provider does not support the use of filters.

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What that means is that the alias provider doesn't support filtering.

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Because filtering, there's a certain technical,

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programmatic way that filtering is described,

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and the filter parameter must use that,

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and Get‑ChildItem can't work in the alias with that filter.

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But that's fine because we have alternatives, right?

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We could do ‑name.

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That doesn't seem to work either.

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But see, you've got to try these things.

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Let's try the include trick.

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I still have to use Recurse though.

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Now that works, although something like this using the path might be even easier.

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So there are a number of ways that you can filter using different parameters,

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but you may have to experiment to find the right combination of

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parameters to get you the results you want,

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maybe with the least amount of work.

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Now let me give you another example of where reading the help is very important.

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So I'm going to run get‑ciminstance and get all of the

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Win32_SystemDriver instances on my computer.

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Alright, so I get a lot of good information, but it was more though than I want.

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Really,

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all I care about is I just want to see the ones where they're

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running and the servicetype is the file system driver.

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So get‑ciminstance has a filter parameter,

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which is basically like a where clause in the SQL query.

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Type this out here.

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Alright,

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So what I'm doing with the command here is

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get‑ciminstances from that Win32_SystemDriver class,

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and then the filter is basically,

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get me everything where the state property is equal to running and the

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servicetype is equal to file system driver. Query that I'm doing here,

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this is a WQL query, a WMI type query, this uses the traditional

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operators. Notice I'm using the equal sign.

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I'm not using a PowerShell operator,

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so the filter is generating a query that will limit kind of like a SQL

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query and return back just the information that I want.

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This becomes super important when you start scripting at scale.

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If I were to run this command against 500 servers and bring the results back,

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I want to have those 500 servers limit at the source and not

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bring everything back to me, and then I filter. That's why early filtering is so important.