Identify Windows 2012 Server core

In PowerShell:

Get-WMIObject Win32_OptionalFeature | where Name -eq 'Server-Gui-Shell' | Select InstallState

returns 1 on a full server and 2 on a server core install.

Edit:

While my answer above is correct, there are two problems with it:

1. When using this command on a workstation, it returns nothing, so you have to add an extra check for this.

2. It is slow, when I tried it, it took between 600 and 3500 milliseconds.

So the more pragmatic approach is to just check for the existence of a certain file:

(Test-Path "$env:windir\explorer.exe")

This returns $false for a Server Core installations and $true for all others and it takes one millisecond to execute.

Funny, that MSDN article you linked contained the answer:

PRODUCT_*_SERVER_CORE values are not returned in Windows Server 2012.

This is because Server 2012 can be freely converted between "Server Core" and "full" installation simply by adding or removing the appropriate features.

You will want to check for the presence or absence of those features (e.g. Server-Gui-Mgmt-Infra, Server-Gui-Shell, Desktop-Experience).

As the GUI is just a feature, you can query the list of installed features

Just testing this in powershell on a server here worked well enough:

Dump a list of features to grab the name

Get-WmiObject Win32_OptionalFeature > features.txt

Searching the text of features.txt tells me that the feature is named 'Server-Gui-Mgmt' (other features may be installed too as Michael notes in his answer, so you can test for those too), and we can search to see if that's present

Get-WmiObject -query "select * from Win32_OptionalFeature where name = 'Server-Gui'"

I would use Win32_ServerFeature, it is a much smaller class and only contains the roles installed on the server. Queries using Win32_Server feature should return much quicker.

Get-WmiObject -Query "Select * FROM Win32_ServerFeature WHERE Name = 'Server Graphical Shell'" 

I suspect that since they are essentially the same in 2012 with just a few optional features to set them apart, you could query the features instead.

this article is a reference for the Win32_OptionalFeature class, which will allow you to query the features. The optional features are defined as Server-Gui-Mgmt-Infra, Server-Gui-Shell and Desktop-Experience, as outlined in this article.

You can query for the 3 of them and use Boolean AND and NOT logic to select servers which have none of these features installed.