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Let's jump back into PowerShell and let me give you a quick

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demonstration of how this variable expansion process works or,

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in some cases, doesn't work.

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Okay, variable expansion in PowerShell can be a tricky thing,

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especially for a lot of PowerShell beginners.

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I see this all the time in classes that I teach and speaking at conferences.

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So,

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let me go through a few demonstrations here so you can

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see how this works and what to expect.

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So, let's say I've got this variable $PSEdition, and you can see it says Core.

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So I want to create a string using double quotes,

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and it says I'm running the, and then $PSEdition,

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the variable name, of PowerShell,

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and PowerShell writes a string and replaces $PSEdition,

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that variable name, with the value of the variable.

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Again,

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this is something that you probably will use more when you get to scripting,

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but I wanted to show it to you in the console because you

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can also use this up from the console.

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The variable expression in double quotes,

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that's the key here, works nicely with a simple variable like $PSEdition or $PID,

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anything has a a single value.

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This is where it gets complex.

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So let's get the WinRM service, save that to a variable.

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And we can look at a few properties here.

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So I've got name and status.

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I want to create a string, a similar string.

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This is basically going to say the WinRM service is running,

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at least that's what I'm expecting.

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A lot of people will think, well,

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I'll just do the same thing that I just did with

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the with that $PSEdition example.

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The $svc.name is currently $svc.status, it's using that object notation.

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And that fails.

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You instead get the System.ServiceProcess.ServiceController.name,

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blah, blah, blah.

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Yeah, what happened?

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What happened is that PowerShell saw $service,

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$svc, and said okay, I see that that is an object.

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Now I know you want the name property,

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but I don't know how to expand the property to give you just that single value.

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So I'm just going to kind of do my best effort here, and so I'm going to

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show you the object and the property that you wanted, actually the name of

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the property. So you can see its name and status.

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What you need to do is use a subexpression.

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Now it's a little tricky, but if you think about it

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in a moment it will make sense.

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So let me type it out here and then explain what's going on.

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So, I have The, and then the next part is the variable part,

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the fill in the blank.

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I still have $service,

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$svc.name, but then in parentheses I have a dollar sign in front of that,

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and the same thing for $svc.status. PowerShell will take that dollar sign,

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parentheses, and then the code inside it and run it or evaluate it and in

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essence say oh, $svc.name, that is WinRM, $svc.status, that is running. And

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it will then take that in‑memory value, that's kind of an ad hoc temporary

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variable, and then plug it into the placeholder that you have there in the

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string.

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And now I get the results that I am expecting.

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So if you have a complex string that you're trying to create with

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objects and whatnot, subexpression, that is the key to making that

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work. Again, make sure you use double quotes.

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If you use single quotes,

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PowerShell assumes that anything you put inside those single

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quotes is treated as a literal string and it will not try to

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replace it or expand it or anything like that.

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Now,

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one thing I want to point out is learn to use the

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subexpressions as I've shown you here.

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What I really don't want to see is if you show me code

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that does this. Now it will work, but it's really, to my

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way of thinking, an old school,

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almost a VBScript approach to PowerShell. I'm concatenating

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much of the strings together to get the result that I want.

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When I see code like this,

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I know that whoever is writing this is still thinking about text, they're

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thinking about how do I join pieces of text together?

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They're not thinking about PowerShell as an object.

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The subexpression forces you to think, okay,

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$svc is an object, how do I work with that object?

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Don't be thinking about how do I pull out a piece of string,

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a piece of text that I can work with, because that will lead you down the path

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of concatenation. Personally, the plus sign is for addition,

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for adding numbers, not for adding strings together.

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All right, enough of my little sermon on concatenation with strings. Let's hop back to the slides and finish up this module.