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This is how we've used Where‑Objects from the earliest days of PowerShell,

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you run some command and then pipe the results to Where‑Object.

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Remember, Where‑Object has an alias of where,

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which is what you'll typically see in examples. Where‑Object uses

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a script block to test if the incoming objects meet some

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requirement. The script block can be as complicated or as long as

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you need it to be, although, as you might imagine,

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simple is usually better.

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The $_ character, or set of characters, means the

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current object in the pipeline.

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Now this script block that you see on the screen is looking at

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the status property of each incoming service object and it's

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then performing a simple comparison.

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Where filters usually use some type of comparison operator.

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In this example,

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I'm using the ‑eq, or equals, operator. If you need to,

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there is a help topic that you should look at to learn

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more about comparison operators.

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In this example,

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if the status property of the service object is equal to running,

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Where‑Object will pass that object to the next command in the pipeline.

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If it doesn't, it just ignores that object.

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Now as I said, the script block can be as complex as you need it to be,

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but in the end it has to give you a true or false result.

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Only objects that give you a true result are passed on.

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Starting a few versions ago,

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PowerShell introduced a simplified syntax for Where‑Object. The concept's

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unchanged, you're applying some type of filtering test,

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but the syntax is relaxed.

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You don't use $_ and you don't need to create an explicit

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script block with the curly braces.

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This type of syntax works fine with simple comparisons.

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What you see here is an equivalent version of my previous example.

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All you need is the property name.

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The $_ is implied.

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But Where‑Object is still comparing, in this case,

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the status property of each service object, and only passing on those

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where the value of status is equal to running. And just to keep you on

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your toes, there's yet another way to use Where‑Object. Instead of

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using $_ in the script block, you can use $psitem.

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The concept is still the same,

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but instead of using $_ to represent the object, you can use that $psitem.

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However, as I'd like to say in PowerShell,

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just because you can do something doesn't mean you should.

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Personally, I'm not a big fan of $psitem.

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I suggest that you stick with the traditional

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syntax using a script block and $_.

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When you find examples online and in the PowerShell help, this is most

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likely what you're going to find anyway. It works everywhere,

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and when you get to scripting,

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this is definitely the form that I would recommend.

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Plus, if your filtering expression is going to be complex,

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such as the one I have here on the screen, then you

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have no choice but to use this syntax, so why not just use it all the time?

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Still, as you gain experience,

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if you want to use the simple syntax of the prompt for a

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simple comparison to save some typing, go right ahead.

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Finally,

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don't be surprised if you find yourself combining early and

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late filtering ideas in the same command.

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The first part of the command with Get‑Service is using the

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‑name parameter to limit or filter initial results to services

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with the name that starts with w.

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This small number of service objects is then passed to

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Where‑Object to filter again to only show services that are

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running and have a manual start type.

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Now, this is an admittedly artificial example, but the point I'm trying

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to make is that you need to get in the habit of filtering early and using

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Where‑Object when you have no other choices. Get‑Service doesn't have an

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option to filter on the status,

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so I really have no choice but to use Where‑Object. What I

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don't want to see are examples like this.

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These are things that I've seen from beginner

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PowerShell students over the years.

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Yeah, these commands will work,

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but that doesn't mean it's the right way. For something like

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getting services on the local machine, it really won't make

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any difference performance‑wise.

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But I want you to get in the habit of filtering the

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right way, the PowerShell way, because eventually it will matter.

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Building good PowerShell practices that you use all the time will go a

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long way in helping you get the most out of PowerShell, and I think you'll find it easier to use.