How to get a list of COM objects from the registry

Today I was looking for the COM ProgID for Excel on my machine and my previous approach of using WMI didn’t work.

PS> gwmi Win32_COMSetting | ?{ $_.ProgId -match "Excel" }
PS>

1 2	PS> gwmi Win32_COMSetting \| ?{ $_.ProgId -match "Excel" } PS>

That’s not correct as I can create a new COM object by referring to Excel.Application.

Since ProgIDs are found in the registry under HKEY_LOCAL_MACHINE\SOFTWARE\Classes I figured that would be a good place to get an exhaustive list from. Under this key there are three types of subkeys:

Subkeys for each file extension registered with the system, each of which has a (Default) entry with the ProgID and also a subkey with the ProgID. Not all these ProgIDs seem to be valid though (based on my testing), so it’s best to go by the other set of subkeys detailed below.
Subkeys for each ProgID – usually of both ProgID formats <Program>.<Component>.<Version> and <Program>.<Component> – again, not all valid, but a good test of validity (based on my testing) being whether they contain a subkey called CLSID.
Subkeys such as “Unknown”, “Undecided”, etc and also some that look like ProgIDs but are not in the correct format (for instance: they don’t contain the <Component>.<Version> bit, or contain spaces and underscores (not allowed)

So a sensible way to filter out ProgIDs seems to be to check for subkeys of the format <Program>.<Component>.<Version> (the <Version> being optional) and to further filter out those which have a CLSID subkey.

Thus we have the following:

Get-ChildItem "HKLM:\SOFTWARE\Classes" | 
  ?{ ($_.PSChildName -match "^[a-z]+\.[a-z]+(\.\d+)?$") -and ($_.GetSubKeyNames() -contains "CLSID") } | ft PSChildName

1 2	Get-ChildItem "HKLM:\SOFTWARE\Classes" \| ?{ ($_.PSChildName -match "^[a-z]+\.[a-z]+(\.\d+)?$") -and ($_.GetSubKeyNames() -contains "CLSID") } \| ft PSChildName

And to search for a specific application, one can do:

Get-ChildItem "HKLM:\SOFTWARE\Classes" | 
  ?{ ($_.PSChildName -match "^[a-z]+\.[a-z]+(\.\d+)?$") -and ($_.GetSubKeyNames() -contains "CLSID") } | 
  ?{ $_.PSChildName -match "Excel" } | ft PSChildName

Get-ChildItem "HKLM:\SOFTWARE\Classes" |

?{ ($_.PSChildName -match "^[a-z]+\.[a-z]+(\.\d+)?$") -and ($_.GetSubKeyNames() -contains "CLSID") } |

?{ $_.PSChildName -match "Excel" } | ft PSChildName