Powershell – Quite note on Objects
I’m sure this comes as no surprise to anyone who’s dabbled in Powershell, but just about everything in Powershell has an Object underneath. The results we see on screen come from those objects and it’s only when those results are formatted, output, captured, etc that they cease to be an object. This drives much of the power in Powershell. You can set a variable to the contents of an object or part of an object and use that later.
Typically objects will have properties and methods. Properties define what an object “is” – e.g., Red, Small, Named, etc. Methods define what an object can do – e.g., Write, Read, Slice, Mix, etc. There are quite a few internal methods and properties that are common across the internal Powershell objects. You can find these by piping the object to the “Get-Member” cmdlet.
$host | Get-Member
You can add your own properties and methods to objects easily by calling the Add-Member Cmdlet. The most direct way to do this seems to be by piping the object to the Add-Member Cmdlet.
$host | Add-Member –Member NoteProperty –Name PropertyName –Value PropertyValue
As Powershell is based on MS technologies, it makes sense that you can use the .NET Framework to work with objects. I will admit that I’m not as familiar with the wide variety of .NET objects so will not try to go into detail. For one example, here’s a way to call the .NET framework to look up a DNS name by IP address.[system.Net.Dns]::GetHostByAddress("220.127.116.11")
Perhaps a more useful class would be System.Environment, first by querying its Static members:[System.Environment] | Get-Member -Static
You can see that there are a lot of members that are useful. If we choose one and don’t enter valid parameter data, we can even get useful error messages at times. For example, the following will return an error with valid parameters in the message:[system.environment]::GetFolderPath("z")
We can tell by the error message, that some valid parameters would be Desktop, Programs, MyDocuments, Home, etc. Entering a valid parameter in this case will then return the path stored in the Environment for that variable.
You can even define your own objects using the New-Object Cmdlet. With no parameters, this creates an empty object. You can create objects of various types by passing the type as the first parameter to the New-Object cmdlet. If you set a variable to an object, you need to be careful about type casting. Setting a variable to a string containing a date will not necessarily cause that variable to be an object of type System.DateTime. It will most likely be a System.String. You may need to explicitly cast the object as the type you desire or force the value to be of the type you desire in order to cast the object as the correct/desired type.
You can call on COM objects, .NET objects, Powershell objects, Assemblies, and probably more than I’ve listed here as long as you know the name or way to call those objects. I’m still learning this are of Powershell, but hope to expand on this in future posts.