Determine installed PowerShell version

Question

How can I determine what version of PowerShell is installed on a computer, and indeed if it is installed at all?

Answer 1

$host.version is just plain wrong/unreliable. This gives you the version of the hosting executable (powershell.exe, powergui.exe, powershell_ise.exe, powershellplus.exe etc) and not the version of the engine itself.

The engine version is contained in $psversiontable.psversion. For PowerShell 1.0, this variable does not exist, so obviously if this variable is not available it is entirely safe to assume the engine is 1.0, obviously.