Creating COM Objects with PowerShell

Dangling COM objects

No Excel processes are currently running;

get-process -name excel -ea ignore

Create an Excel process using COM:

$xls = new-object -com excel.application
$xls.visible = $true

get-process reports the Excel process:

get-process -name excel -ea ignore

Quit Excel:

$xls.Quit()

Even though Excel has become invisible, the process is still running:

get-process -name excel -ea ignore

Get rid of the process:

$null = [System.Runtime.Interopservices.Marshal]::ReleaseComObject($xls)

Verify process is gone:

get-process -name excel -ea ignore

Returned object type

Typically, new-object -com … returns a System.__ComObject object. In special cases however, it returns an «interop» object that wraps the COM Object.

This behaviour is demonstrated in the following simple example.

First, we create two COM objects …

PS C:\> $fso = new-object -com scripting.filesystemobject
PS C:\> $xls = new-object -com excel.application

… and then determine their types:

PS C:\> $fso.GetType().FullName
System.__ComObject

PS C:\> $xls.GetType().FullName
Microsoft.Office.Interop.Excel.ApplicationClass

I wondered why new-object -com does not always return a __ComObject object. The explanation seems to be related to the way in which COM Objects are registered with the registry.

When I used new-object -com progId, the CLSID that is associated with prog.id was determined. The value of this CLSID is found in the registry as default value of the registry key HKEY_CLASSES_ROOT\prog.id\CLSID:

$null = new-psDrive -name HKCR -psProvider registry -root HKEY_CLASSES_ROOT

$clsid_xls = get-itemPropertyValue -name '(default)' HKCR:\excel.application\CLSID
$clsid_fso = get-itemPropertyValue -name '(default)' HKCR:\scripting.filesystemobject\CLSID

write-host "CLSIDs: xls: $clsid_xls, fso: $clsid_fso"
CLSIDs: xls: {00024500-0000-0000-C000-000000000046}, fso: {0D43FE01-F093-11CF-8940-00A0C9054228}

Each of these CLSIDs has a registry key named InprocServer32 that is found under the key HKEY_CLASSES_ROOT\CLSID\{clsid}

If we look up these keys in regedit.exe, we find some differences.

In-proc server for file system object

In the case of the file system object, «only» a DLL is registred:

In-proc server for Excel

However, for the Excel object, an assembly and a (default?) class is registered: