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The power of PowerShell: Essential tips Windows admins will love

Adam Bertram | Nov. 6, 2015
Make the most of Microsoft’s command line by mastering the nuances of the PowerShell language.

The output will now include our new custom property called ServerName.

ServerName Output
Click on image to enlarge.

I had to change the code quite a bit so allow me to break it down. First, notice how I moved the original properties being passed to Select-Object (IPV4Address,ResponseTime,TimeToLive) above, then passed $selectProperties to Select-Object that way. This was simply to reduce the length of the line. It behaves exactly the same as if I simply passed them directly to Select-Object as I did in the console previously.

What functionality did change was the addition of another property in $selectProperties to pass to Select-Object. Notice it wasn't a string like the others but a hashtable with two elements inside: Name and Expression. This is called a calculated property. This is how using Select-Object you can essentially create properties on the fly. Every property you'd like to add has to be in a hashtable with a Name and an Expression as key names. The Name key's value is the name you'd like to call the object property. The Expression key's value always has to be a script block. Notice $serverName is enclosed in curly braces. This is how $serverName can be expanded to the actual server names as each server is tested in the text file.

This can be used not only to create new properties but to modify existing properties as well. Maybe I'd like to append a ms label to all the TimeToLive properties to signify the number is in milliseconds. Instead of specifying the name of the TimeToLive property I would instead create a hashtable and concatenate the foreach pipeline value of TimeToLive represented by $_.TimeToLive with ms to create a single string.

TimeToLive script
Click on image to enlarge.
TimeToLive output

Using calculated properties with Select-Object are very convenient but beware: They come with a performance hit. I don't recommend using calculated properties if you're working with large data sets as it can drastically slow down your script. But if you have fairly small data sets with 100 or fewer elements the performance hit will be minimal.

Custom object creation

Objects abound in PowerShell, and it only makes sense for us to be able to create our own objects from scratch. Fortunately, PowerShell provides us with a few different ways to do that. In this tip, I'll cover three methods to create custom objects.

In PowerShell, an object is of a specific type. When creating custom objects, the most common type of object type is System.Management.Automation.PSCustomObject. This is the kind of object we'll create in this article. Also, an object has one or more properties of various types. In this article, we'll focus on NoteProperty types.

 

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