Referencing System.Management.Automation.dll in a correct, multi-OS friendly way
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I am writing a piece of C# that will invoke PS scripts. As part of this I’m referencing System.Management.Automation.dll, the library that the PS guys expose that makes my life easier. I assume this is the right library to use (internet searching seems to confirm but if I’m wrong let me know).
This library is installed as part of the PS install / Windows SDK.

I’m finding two weird things about this library:

 - I always have to reference it with a full path (even though it’s in
   the GAC?)
 - The path is different on different OSs

I’ve found it in the following paths (ignoring GAC paths which I assume I shouldn’t use):

 - win2k8 r2: C:\Program Files\Reference Assemblies\Microsoft\WindowsPowerShell\v1.0
 - Win7 x64: C:\Program Files (x86)\Reference Assemblies\Microsoft\WindowsPowerShell\v1.0\

What's the correct way to reference this assembly in a multi-OS-version friendly way?