PowerShell object member is null from C#

Question

I'm trying to run Get-NetAdapter -Physical from C#. If I run it from PS itself the resulting table has InterfaceDescription and MacAddress columns with meaningful values, however doing this in C#:

using (var ps = PowerShell.Create())
{
    ps.AddCommand("Get-NetAdapter");
    ps.AddParameter("Physical");
    var results = ps.Invoke();
[...error checking here...]
    foreach (var result in results)
    {
[...null check here...]
        var name = result.Members["InterfaceDescription"].Value;
        var mac = result.Members["MacAddress"].Value;
    }
}

The second line in the foreach throws a NullReferenceException at the left-hand side of .Value. If I change Members to Properties the result is the same. name is fine. I've also tried using dynamic to get to the members but that doesn't seem to work either. How can I get to the object that I can obtain in PowerShell through thing.MacAddress?

jbsmith · Accepted Answer · 2019-05-20 16:57:55Z

You're seeing this because "MacAddress" is a ScriptProperty:

Get-NetAdapter -Physical | Get-Member -Name MacAddress | fl *


TypeName   : Microsoft.Management.Infrastructure.CimInstance#ROOT/StandardCimv2/MSFT_NetAdapter
Name       : MacAddress
MemberType : ScriptProperty
Definition : System.Object MacAddress {get=$out = ""
                       if (($this.NetworkAddresses -ne $null) -and
                           ($this.NetworkAddresses.length -ge 1))
                       {
                         $MacAddress = $this.NetworkAddresses[0];
                       }
                       if($MacAddress -ne $null)
                       {
                           for($i = 0; $i -lt $MacAddress.Length; )
                           {
                               $out += $MacAddress[$i++];
                               if($i -eq $MacAddress.Length)
                               {
                                 break;
                               }
                               $out += $MacAddress[$i++];
                               if ($i -lt $MacAddress.Length)
                               {
                                 $out += '-';
                               }
                           }
                       }
                       $out;set=param($newValue)
                       $MacAddress = $newValue -replace '(:|-)'
                       $this.NetworkAddresses = $MacAddress;}

As described in this answer, if you just pipe the results to Select-Object *, the ScriptProperty will be evaluated in the PowerShell runspace and returned as a Note instead.

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