Export Specific Registry Keys

Leaving the aspect of targeting multiple remote computers aside (for which you'd need Invoke-Command -ComputerName $Servers { ... }), you can simplify your code as follows (I'm also omitting the Export-Csv call):

$regPath = 'HKLM:\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces'
Get-ItemProperty $regPath\* |
  Select-Object DhcpIPAddress,DhcpNameServer,DhcpServer,DhcpDefaultGateway |
    Where-Object { $_.psobject.Properties.Value -ne $null }

• Using wildcard path $regPath\* implicitly loops over all the child keys in $regPath and retrieves their properties.

• Where-Object { $_.psobject.Properties.Value -ne $null } filters out any of the custom objects created by the Select-Object call that do not at least have one non-$null property value, using the intrinsic .psobject property.

More work is needed in order to:

• Add a Server property that reflects the executing machine's host name.

• Convert the array-valued DhcpDefaultGateway property to a string-valued one, by joining potentially multiple addressed with , , so that exporting to a CSV works meaningfully (array-valued properties end up as verbatim System.String[] in a CSV).

Both can be achieved via calculated properties:

$regPath = 'HKLM:\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces'
Get-ItemProperty $regPath\* |
    Select-Object @{
                     Name='Server';
                     Expression = { $env:COMPUTERNAME }
                  }, 
                  DhcpIPAddress, DhcpNameServer, DhcpServer, 
                  @{
                    Name = 'DhcpDefaultGateway';
                    Expression = { $_.DhcpDefaultGateway -join ', ' }
                  } |
      Where-Object { 
        $_.psobject.Properties.Where({ $_.Name -ne 'Server' }).Value -ne $null 
      }

Note: If you want to collect all information in a single CSV file on the calling computer, across all servers, do something like the following:

Invoke-Command -Servers $Servers { ... } | 
  Select-Object * -Exclude PS*, RunspaceId |
    Export-Csv C:\temp\TCPIP_Interface_Details.csv NoTypeInformation

• -Exclude PS*, RunspaceId excludes the properties that PowerShell remoting automatically adds to all output objects.

As for what you tried:

• Your Get-ChildItem call returned objects of type [Microsoft.Win32.RegistryKey].

• Passing them to Get-ItemProperty -Path stringifies them, resulting in a registry-native path to be reported; e.g.:

  HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces\{223a2c0a-88d9-11e6-b808-806e6f6e6963}
  

• PowerShell doesn't directly recognize such paths and assumes that they are (relative) file-system paths. To force their interpretation as a registry path, you have tree options:

  • Preferably, use the pipeline to supply the input path:

     # Note: This binds the .PSPath property value to the -LiteralPath parameter.
     $interface | Get-ItemProperty
    

  • Use the .PSPath property that PowerShell decorates the objects with:

     # Note: Parameter -Path implied; for full robustness, use -LiteralPath
     Get-ItemProperty $interface.PSPath
    

  • Prepend the registry:: provider prefix to the registry-native path resulting from the stringification:

     Get-ItemProperty registry::$interface
    

• I presume that Where-Object -Like DhcpIPAddress,DhcpNameServer,DhcpServer,DhcpDefaultGateway is an attempt to filter out "empty" objects resulting from the Select-Object call, so that only objects that have actual values for the selected properties are returned and exported to CSV.

  • However, even syntactically this approach cannot work, because as of PowerShell 7.2.x you cannot implicitly apply an operation to each input object as a whole using simplified syntax; instead, you must specify a property to operate on, via the -Property parameter, to which the first positional argument implicitly binds.

    • That said, it would be convenient to be able to operate implicitly on each input object as a whole, and GitHub issue #8357 proposes adding support for it.

  • Thus, your command is equivalent to the following, which fails, because -Property only supports a single property name (string):

    Where-Object -Property DhcpIPAddress,DhcpNameServer,DhcpServer,DhcpDefaultGateway -Like
    

  • Your logic therefore requires passing a script block ({ ... }) to Where-Object's (positionally implied) -FilterScript parameter, in which the input object as a whole can be referenced as usual, via the automatic $_ variable. However, even your -like operation wouldn't work as intended; see the command at the top for how to filter out objects with only $null property values.

Each $interface is an object with properties of which .Path is the interesting one.

Try:

$Servers = $env:COMPUTERNAME # Get-Content -Path 

$result = foreach ($vm in $Servers) {
    Invoke-Command -ComputerName $vm -ScriptBlock {
        Get-ChildItem -Path 'HKLM:\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces' | ForEach-Object {
            Get-ItemProperty -Path $_.PSPath | Where-Object { $_.PsObject.Properties.Name -like 'Dhcp*' }
        }
    } | Select-Object -Property @{Name = 'ComputerName'; Expression = {$_.PSComputerName}}, 
                                DhcpIPAddress,
                                @{Name = 'DhcpNameServer'; Expression = {$_.DhcpNameServer -split ' ' -join '; '}},
                                DhcpServer, 
                                @{Name = 'DhcpDefaultGateway'; Expression = {$_.DhcpDefaultGateway -join '; '}}
}
$result | Export-Csv -Path "C:\temp\TCPIP_Interface_Details.csv" -NoTypeInformation

^{Of course, you may need to add parameter -Credential to the Invoke-Command cmdlet and supply a valid administrator credential}