"Write-Error" (write in Powershell, used in C#) works BUT Write-Debug doesn´t work - Why?

Question

I have written a program with C#, that creates a logfile and fills this by using log4net. This program starts powershell-scripts. The scripts use log4net, too. It works:

> C#:   
> ps.Runspace.SessionStateProxy.SetVariable("myMethod",(Action<Level,string>)myMethod);
> ps.AddCommand(System.IO.Path.Combine(pathScripts, testSkripte[i].ToString()));  
> ps.Invoke();

> Powershell:                     
> $ScriptLog.Invoke([log4net.Core.Level]::Debug, "TestFile_Debug")                     
> $ScriptLog.Invoke([log4net.Core.Level]::Warn, "TestFile_Warn") $ScriptLog         
> $ScriptLog.Invoke([log4net.Core.Level]::Error, "TestFile_Error")

Now I want add to use the standard Write-Error, Write-Debug, etc. CMDlets in my Script.
(looks like here - answer of Hinek).

Powershell:
   Write-Warning "Write-Warning"      
  AND         
   Write-Error "Write-Error"

works, but the following doesn´t work:

Write-Debug "Write-Debug"         (I don´t get an item in my logfile)   OR    
Write-Debug "Write-Debug" -debug  (for this I get an item in my logfile, but ...)

... I get an error in my logfile, too. The error looks like this:

[2010-10-22 13:10:58,097] DEBUG : Write-Debug                                     
[2010-10-22 13:10:58,113] ERROR : Cannot invoke this function because the current
                                  host does not implement it

(I think to have all namespaces.)

What the error-message means and what can I do again this?

thanks

Answer 1

Here is a workaround solution: override the default command Write-Debug (which is actually not implemented) with a function:

function global:Write-Debug
(
    [string]
    $Message,
    [switch]
    $Debug
)
{
    # check both the $Debug switch and the $DebugPreference variable:
    if ($Debug -or ($DebugPreference -ne 'SilentlyContinue')) {
        # do job; in this demo just write to the console:
        [Console]::WriteLine("DEBUG: $Message")
    }
}

In C# put this code into a string and invoke it once in the same runspace where the main script will be invoked. This “profile” code installs the global function Write-Debug which is semantically the same as the original cmdlet. Then, when the main code calls Write-Debug that function is called, not the default cmdlet.

P.S. I have not tried this way, I prefer to use my own host (see my other answer). But this way should work fine in many cases (not all, perhaps).