PowerShell v2 CTP3 advanced function parameter '-WarningAction' not working

Tuesday, November 03, 2009 1:42 AMMichael Ward27

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I'm currently in the process of writing some PowerShell scripts for managing our environment, and want to make use of the 'WarningAction' common parameter. However it doesn't seem to work :-(.

I'm using the [CmdletBinding()] attribute in my script to enable common parameters (http://msdn.microsoft.com/en-us/library/dd901844(VS.85).aspx).

Consider the following PowerShell v2 CTP3 script test.ps1:

==============
```
[CmdletBinding()]
param()

Write-Host "warning: $WarningPreference"
Write-Host "error: $ErrorActionPreference"

Write-Warning "b"
Write-Error "c"
```
==============

If I execute the script as follows:

==============
```
PS > .\test.ps1 -ErrorAction SilentlyContinue
warning: Continue
error: SilentlyContinue
WARNING: b
```
==============

As expected, the $ErrorActionPreference is set to 'SilentlyContinue', and the output from the Write-Error cmd is suppressed.

However, if I execute:

==============
```
PS > .\test.ps1 -WarningAction SilentlyContinue
warning: Continue
error: Continue
WARNING: b
D:\Misc\scripts\PowerShell\test.ps1 : c
At line:1 char:11
+ .\test.ps1 <<<<  -WarningAction SilentlyContinue
    + CategoryInfo          : NotSpecified: (:) [Write-Error], WriteErrorException
    + FullyQualifiedErrorId : Microsoft.PowerShell.Commands.WriteErrorException,test.ps1
```
==============

The $WarningPreference isn't set, and the output from the Write-Warning cmd is not suppressed as would be expected.

Does this happen for anyone else? Or is there something obvious I'm missing?

Running Get-Help indicates that -WarningAction is supported:

==============
PS D:\> Get-Help .\test.ps1
test.ps1 [-Verbose] [-Debug] [-ErrorAction <ActionPreference>] [-WarningAction <ActionPreference>] [-ErrorVariable <String>] [-WarningVariable <String>] [-OutVariable <String>] [-OutBuffer <Int32>]
==============

Thanks
Michael

Note: I have already posted another version of this question in the Scripting Guys forum (see link below). It was suggested I post this here as well.
http://social.technet.microsoft.com/Forums/en/ITCG/thread/1e7ea871-432f-4650-ac1e-5a5a5e663f40
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Answers

Tuesday, November 03, 2009 6:24 AMJoel -Jaykul- BennettMVP

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Believe it or not, for that parameters to take effect you need to use the special methods documented in about_Functions_Advanced_Methods which are all methods of the special magic variable $PSCmdlet ...
```
[CmdletBinding()]
param()

Write-Host "warning: $WarningPreference"
Write-Host "error: $ErrorActionPreference"

$PSCmdlet.WriteWarning( "b" )
$PSCmdlet.WriteError( "c" )
```
The documentation actually says that you "can also use the various Write cmdlets," but at least in this case, it's wrong. :-(
- Marked As Answer byMervyn ZhangMSFT, ModeratorFriday, November 06, 2009 5:49 AM
- Marked As Answer byMarco ShawMVP, ModeratorTuesday, November 03, 2009 12:03 PM
- Unmarked As Answer byMarco ShawMVP, ModeratorThursday, November 05, 2009 1:55 AM
- Unproposed As Answer byMarco ShawMVP, ModeratorThursday, November 05, 2009 1:55 AM
- Proposed As Answer byJoel -Jaykul- BennettMVPTuesday, November 03, 2009 6:28 AM
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Thursday, November 05, 2009 6:31 AMJoel -Jaykul- BennettMVP

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Ok, now, this is mostly a joke, but .. if you REALLY need those warnings to behave, it has to look something like this:

function TestWarningA {[CmdletBinding()]param()
   # This has no effect on the WarningVariable, but without it the warnings are displayed in the host
   if($PSBoundParameters.ContainsKey("WarningAction")){ $local:WarningPreference = $PSBoundParameters['WarningAction'] }

   Write-Host "Script A: $WarningPreference"

   $PSCmdlet.WriteWarning("WA1") # this is the only thing affected by -WarningAction
   if($PSBoundParameters.ContainsKey("WarningVariable")){
      Write-Warning "WA2" -WarningVariable $("+$($PSBoundParameters['WarningVariable'].TrimStart('+'))")
   } else {
      Write-Warning "WA2"
   }

   $PSCmdlet.WriteError((new-object System.Management.Automation.ErrorRecord( (new-object System.Exception "EA1"), "TestError", "NotSpecified", $null)))
   Write-Error "EA2"

   if($PSBoundParameters.ContainsKey("WarningVariable")){
      TestWarningB -WarningVariable $("+$($PSBoundParameters['WarningVariable'].TrimStart('+'))")
   } else {
      TestWarningB
   }

}

function TestWarningB {[CmdletBinding()]param()

   Write-Host "Script B: $WarningPreference $($PSBoundParameters['WarningVariable'])"

   $PSCmdlet.WriteWarning("WB1")
   if($PSBoundParameters.ContainsKey("WarningVariable")){
      Write-Warning "WB2" -WarningVariable $("+$($PSBoundParameters['WarningVariable'].TrimStart('+'))")
   } else {
      Write-Warning "WB2"
   }

   $PSCmdlet.WriteError( (new-object System.Management.Automation.ErrorRecord( (new-object System.Exception "EB1"), "TestError", "NotSpecified", $null)) )
   Write-Error "EB2"
}

TestWarningA -WarningAction:SilentlyContinue -WarningVariable wv -ErrorAction:SilentlyContinue -ErrorVariable ev
- Marked As Answer byMervyn ZhangMSFT, ModeratorFriday, November 06, 2009 5:48 AM
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Tuesday, November 03, 2009 2:15 AMMarco ShawMVP, Moderator

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At this point, v2 has been offiicially released for all platforms. That being said, I did try this on PowerShell v2 on Server 2008 R2 and got the same error. I'll ask around and make sure to test on a RTM release...
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Tuesday, November 03, 2009 6:24 AMJoel -Jaykul- BennettMVP

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Believe it or not, for that parameters to take effect you need to use the special methods documented in about_Functions_Advanced_Methods which are all methods of the special magic variable $PSCmdlet ...
```
[CmdletBinding()]
param()

Write-Host "warning: $WarningPreference"
Write-Host "error: $ErrorActionPreference"

$PSCmdlet.WriteWarning( "b" )
$PSCmdlet.WriteError( "c" )
```
The documentation actually says that you "can also use the various Write cmdlets," but at least in this case, it's wrong. :-(
- Marked As Answer byMervyn ZhangMSFT, ModeratorFriday, November 06, 2009 5:49 AM
- Marked As Answer byMarco ShawMVP, ModeratorTuesday, November 03, 2009 12:03 PM
- Unmarked As Answer byMarco ShawMVP, ModeratorThursday, November 05, 2009 1:55 AM
- Unproposed As Answer byMarco ShawMVP, ModeratorThursday, November 05, 2009 1:55 AM
- Proposed As Answer byJoel -Jaykul- BennettMVPTuesday, November 03, 2009 6:28 AM
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Wednesday, November 04, 2009 1:43 AMMichael Ward27

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Ahhh... thanks Joel, that does work! So is that a bug or what? Write-Error and the others like Write-Verbose and Write-Debug seem to work fine, it's just Write-Warning that isn't.

So using the $PSCmdlet.WriteWarning() format I was able suppress the error and capture it using -WarningVariable. Mission accomplished!

Michael

Oh btw I also tried this in Windows 7, same problem. So looks like this is a problem in RTM.
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Wednesday, November 04, 2009 11:45 PMMichael Ward27

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Ok... after playing around a bit more with this, I've stumbled across my next problem. Using $PSCmdlet.WriteWarning(), how can I pass the warnings back through multiple levels of calling scripts?

For example, consider the following two scripts:

====
# TestWarningA.ps1
[CmdletBinding()]
param()

Write-Host "Script A"
$PSCmdlet.WriteWarning("A")

.\TestWarningB.ps1
====

and

====
# TestWarningB.ps1
[CmdletBinding()]
param()

Write-Host "Script B"
$PSCmdlet.WriteWarning("B")
====

Executing TestWarningA.ps1 with -WarningAction SilentlyContinue returns:

====
PS D:\> .\TestWarningA.ps1 -WarningAction SilentlyContinue
Script A
Script B
WARNING: B
====

The warning in TestWarningB.ps1 is not suppressed as I had intended and only the first warning is returned to the -WarningVariable. The same scenario but using Write-Error does work as expected. Is there a way to work around this using $PSCmdlet.WriteWarning()?

I need to be able to capture all the warnings from the sub scripts to action appropriately in the master script (e.g. log to event log).

Let me know if I should log this as a new forum entry - will do so if I get no response due to this thread already being marked 'answered'.

Thanks
Michael
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Thursday, November 05, 2009 1:56 AMMarco ShawMVP, Moderator

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I've unmarked Jaykul's response as the answer, but may go back on that later.
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Thursday, November 05, 2009 6:05 AMJoel -Jaykul- BennettMVP

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Ugh. Yeah, it was definitely a bug already, in my opinion, this makes it doubly so.

Marco: aww, you could at least vote me helpful :-P

The problem is that the WarningAction common parameter doesn't actually set/override the value of the $WarningPreference variable the way it's supposed to (try printing it out, you'll see), and therefore the setting isn't propagated to nested commands.

If you put a line: { Get-Variable -Scope Local } in your TestWarningA, you'll see that passing -ErrorAction:SilentlyContinue actually results in the variable being defined for that local scope, but the same is NOT true for the -WarningAction:SilentlyContinue parameter (which it seems should behave the same way).

You could make it work for any given function by adding this at the top:

   if($PSBoundParameters.ContainsKey("WarningAction")){
      $local:WarningPreference = $PSBoundParameters['WarningAction']
   }

I'll send a note to the MVP mailing list, but I filed a bug too: https://connect.microsoft.com/PowerShell/feedback/ViewFeedback.aspx?FeedbackID=508387
- Edited byJoel -Jaykul- BennettMVPThursday, November 05, 2009 6:06 AMlinkifying
- Edited byJoel -Jaykul- BennettMVPThursday, November 05, 2009 6:32 AM
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Thursday, November 05, 2009 6:31 AMJoel -Jaykul- BennettMVP

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Ok, now, this is mostly a joke, but .. if you REALLY need those warnings to behave, it has to look something like this:

function TestWarningA {[CmdletBinding()]param()
   # This has no effect on the WarningVariable, but without it the warnings are displayed in the host
   if($PSBoundParameters.ContainsKey("WarningAction")){ $local:WarningPreference = $PSBoundParameters['WarningAction'] }

   Write-Host "Script A: $WarningPreference"

   $PSCmdlet.WriteWarning("WA1") # this is the only thing affected by -WarningAction
   if($PSBoundParameters.ContainsKey("WarningVariable")){
      Write-Warning "WA2" -WarningVariable $("+$($PSBoundParameters['WarningVariable'].TrimStart('+'))")
   } else {
      Write-Warning "WA2"
   }

   $PSCmdlet.WriteError((new-object System.Management.Automation.ErrorRecord( (new-object System.Exception "EA1"), "TestError", "NotSpecified", $null)))
   Write-Error "EA2"

   if($PSBoundParameters.ContainsKey("WarningVariable")){
      TestWarningB -WarningVariable $("+$($PSBoundParameters['WarningVariable'].TrimStart('+'))")
   } else {
      TestWarningB
   }

}

function TestWarningB {[CmdletBinding()]param()

   Write-Host "Script B: $WarningPreference $($PSBoundParameters['WarningVariable'])"

   $PSCmdlet.WriteWarning("WB1")
   if($PSBoundParameters.ContainsKey("WarningVariable")){
      Write-Warning "WB2" -WarningVariable $("+$($PSBoundParameters['WarningVariable'].TrimStart('+'))")
   } else {
      Write-Warning "WB2"
   }

   $PSCmdlet.WriteError( (new-object System.Management.Automation.ErrorRecord( (new-object System.Exception "EB1"), "TestError", "NotSpecified", $null)) )
   Write-Error "EB2"
}

TestWarningA -WarningAction:SilentlyContinue -WarningVariable wv -ErrorAction:SilentlyContinue -ErrorVariable ev
- Marked As Answer byMervyn ZhangMSFT, ModeratorFriday, November 06, 2009 5:48 AM
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Thursday, November 05, 2009 7:58 PMMichael Ward27

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Wow you guys rock!

Joel - thanks for the code example, no way I could have figured that out myself. Looking at the code I'm not sure I'm that keen on getting it working :-). I didn't mention before, but I actually have three levels of scripts so far calling each other so would have to do this at each level... yikes.

I'm happy knowing it's a bug that will (hopefully!) be fixed sometime... but I won't hold my breath. In the meantime I'll use Write-Error or Write-Output instead (which won't work exactly as I imagined it happening, but will have to make do!).

So Joel answered both my questions, does that mean he gets twice the credit?

Michael
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