Trying to Catch and Exception

[Gary]

Hi there

Today at lunch I tried to learn how to try and catch an exception.

I've been wanting to learn how to read the registry in prep for the
Scripting Games :)

Anyway I can't seem to catch the exact exception I can only catch the
generic system.exception even thought $error tell me I have write name.

Could someone else try for me

<code>
$ErrorActionPreference = "stop"
Try { Get-ItemProperty -Path "HKCU:\Control Panel\Desktop\" -Name Wallpaper2 }
Catch [System.Management.Automation.PSArgumentException] { "caught a
PSArgumentException" }
Catch [system.exception] { "caught a system.exception" }
Finally { "end of script" }
</code>

$error display's

SMessageDetails :
Exception : System.Management.Automation.PSArgumentException:
Prope
rty Wallpaper2 does not exist at path
HKEY_CURRENT_USER
\Control Panel\Desktop\.
TargetObject : Wallpaper2
CategoryInfo : InvalidArgument: (Wallpaper2:String)
[Get-ItemProperty]
, PSArgumentException
FullyQualifiedErrorId :
System.Management.Automation.PSArgumentException,Micros
oft.PowerShell.Commands.GetItemPropertyCommand
ErrorDetails :
InvocationInfo : System.Management.Automation.InvocationInfo
PipelineIterationInfo : {0, 1}

Is anyone able to help me understand where I'm going wrong?

TIA

[Paul B. (USAF)]

I tried:

#####
try
{
Set-Location z:\ -ErrorAction stop
}
catch [System.Management.Automation.DriveNotFoundException]
{
Write-Host $_.exception.gettype().fullname
Write-Host $_.exception.message
}

Post by Gary
Hi there
Today at lunch I tried to learn how to try and catch an exception.
I've been wanting to learn how to read the registry in prep for the
Scripting Games :)
Anyway I can't seem to catch the exact exception I can only catch the
generic system.exception even thought $error tell me I have write name.
Could someone else try for me
<code>
$ErrorActionPreference = "stop"
Try { Get-ItemProperty -Path "HKCU:\Control Panel\Desktop\" -Name Wallpaper2 }
Catch [System.Management.Automation.PSArgumentException] { "caught a
PSArgumentException" }
Catch [system.exception] { "caught a system.exception" }
Finally { "end of script" }
</code>
$error display's
Prope
rty Wallpaper2 does not exist at path
HKEY_CURRENT_USER
\Control Panel\Desktop\.
TargetObject : Wallpaper2
CategoryInfo : InvalidArgument: (Wallpaper2:String)
[Get-ItemProperty]
, PSArgumentException
System.Management.Automation.PSArgumentException,Micros
oft.PowerShell.Commands.GetItemPropertyCommand
InvocationInfo : System.Management.Automation.InvocationInfo
PipelineIterationInfo : {0, 1}
Is anyone able to help me understand where I'm going wrong?
TIA

[Clint Bergman]

Hmm. Strange indeed. I'm not really sure what's going on, but I seem
to be able to create the same issue. For instance:

*** try/catch blocks, terminating error WITHOUT -erroraction STOP ***
PS # gieugnwiu
The term 'gieugnwiu' is not recognized as the name of a cmdlet,
function, script file, or operable program. Check the spelling of the
name, or if a path was included, verify that the path is correct and try
again.
at line:1 char:10
+ gieugnwiu <<<<
+ CategoryInfo : ObjectNotFound: (gieugnwiu:String) [],
CommandNotFoundException
+ FullyQualifiedErrorId : CommandNotFoundException

PS # $error[0].exception.psobject.typenames
System.Management.Automation.CommandNotFoundException
System.Management.Automation.RuntimeException
System.SystemException
System.Exception
System.Object

PS # try { gieugnwiu } catch
[System.Management.Automation.CommandNotFoundException] { 'Got it' }
Got it

So that seems to work as one would expect. We catch the most specific
exception type, and all is well. However, when forcing the termination
with -erroraction stop or by setting $erroractionpreference to "Stop",
it doesn't seem to work the same.

*** try/catch blocks, force termination with $erroractionpreference ***

PS # $ErrorActionPreference = "Stop"
PS # gci oweifjowe
Get-ChildItem : Cannot find path 'C:\Users\Clint\oweifjowe' because it
does not exist.
At
C:\Users\Clint\Documents\WindowsPowerShell\Modules\pscx\Modules\GetChildItem\Pscx.GetChildItem.psm1:71
char:32
+ $scriptCmd = {& <<<< $wrappedCmd @PSBoundParameters }
+ CategoryInfo : ObjectNotFound:
(C:\Users\Clint\oweifjowe:String) [Get-ChildItem], ItemNotFoundException
+ FullyQualifiedErrorId :
PathNotFound,Microsoft.PowerShell.Commands.GetChildItemCommand

PS # $error[0].Exception.psobject.typenames
System.Management.Automation.ItemNotFoundException
System.Management.Automation.SessionStateException
System.Management.Automation.RuntimeException
System.SystemException
System.Exception
System.Object

There's our exception name,
System.Management.Automation.ItemNotFoundException, but it doesn't work
like I would expect:

PS # try { gci oweifjowe } catch
[System.Management.Automation.ItemNotFoundException] { 'got it '}
Get-ChildItem : Cannot find path 'C:\Users\Clint\oweifjowe' because it
does not exist.
At
C:\Users\Clint\Documents\WindowsPowerShell\Modules\pscx\Modules\GetChildItem\Pscx.GetChildItem.psm1:71
char:32
+ $scriptCmd = {& <<<< $wrappedCmd @PSBoundParameters }
+ CategoryInfo : ObjectNotFound:
(C:\Users\Clint\oweifjowe:String) [Get-ChildItem], ItemNotFoundException
+ FullyQualifiedErrorId :
PathNotFound,Microsoft.PowerShell.Commands.GetChildItemCommand

Alright, let's try its parent exception:

PS # try { gci oweifjowe } catch
[System.Management.Automation.SessionStateException] { 'got it '}
Get-ChildItem : Cannot find path 'C:\Users\Clint\oweifjowe' because it
does not exist.
At
C:\Users\Clint\Documents\WindowsPowerShell\Modules\pscx\Modules\GetChildItem\Pscx.GetChildItem.psm1:71
char:32
+ $scriptCmd = {& <<<< $wrappedCmd @PSBoundParameters }
+ CategoryInfo : ObjectNotFound:
(C:\Users\Clint\oweifjowe:String) [Get-ChildItem], ItemNotFoundException
+ FullyQualifiedErrorId :
PathNotFound,Microsoft.PowerShell.Commands.GetChildItemCommand

Nope, bugger, how about the grandparent?

PS # try { gci oweifjowe } catch
[System.Management.Automation.RuntimeException] { 'got it '}
got it

Well, that was caught, but... WHY? Is there something special about the
exceptions generated with -ea stop?

[Clint Bergman]

Post by Gary
$ErrorActionPreference = "stop"
Try { Get-ItemProperty -Path "HKCU:\Control Panel\Desktop\" -Name Wallpaper2 }
Catch [System.Management.Automation.PSArgumentException] { "caught a
PSArgumentException" }
Catch [system.exception] { "caught a system.exception" }
Finally { "end of script" }

Just discovered that the errors that are 'caught' when we force
termination with the $erroractionpreference or with the -erroraction
parameter are of type
System.Management.Automation.ActionPreferenceStopException, and not what
we see when inspecting $error[0]. So try this code:

Try { Get-ItemProperty -Path "HKCU:\Control Panel\Desktop\" -Name
Wallpaper2 }
Catch [System.Management.Automation.ActionPreferenceStopExecution] {
"caught a StopExecution Exception" }
finally { "end of script" }

Instead of trying to trace the errors through the $error variable I used
the errorvariable parameter in the command, and much to my surprise this
was the result:

PS # Get-ItemProperty -Path "HKCU:\Control Panel\Desktop\" -Name
Wallpaper2 -ErrorVariable x
Get-ItemProperty : Property Wallpaper2 does not exist at path
HKEY_CURRENT_USER\Control Panel\Desktop\.
At line:1 char:17
+ Get-ItemProperty <<<< -Path "HKCU:\Control Panel\Desktop\" -Name
Wallpaper2 -ErrorVariable x
+ CategoryInfo : InvalidArgument: (Wallpaper2:String)
[Get-ItemProperty], PSArgumentException
+ FullyQualifiedErrorId :
System.Management.Automation.PSArgumentException,Microsoft.PowerShell.Commands.GetItemPropertyCommand

PS # $x
Command execution stopped because the preference variable
"ErrorActionPreference" or common parameter is set to Stop: Property
Wallpaper2 does
not exist at path HKEY_CURRENT_USER\Control Panel\Desktop\.

PS # $x.Count
1

PS # $x[0].psobject.typenames
System.Management.Automation.ActionPreferenceStopException
System.Management.Automation.RuntimeException
System.SystemException
System.Exception
System.Object

So there we see the ActionPreferenceStopException, and that it is
derived from the RuntimeException class, which explains the behavior I
posted earlier.

So the lesson, I suppose, is be careful with handling exceptions thrown
by erroraction stop!

[Paul B. (USAF)]

Thanks Clint. Definately something I would not have thought of being new
to/learning Try/Catch/Final.

Paul

Post by Clint Bergman

Post by Gary
$ErrorActionPreference = "stop"
Try { Get-ItemProperty -Path "HKCU:\Control Panel\Desktop\" -Name Wallpaper2 }
Catch [System.Management.Automation.PSArgumentException] { "caught a
PSArgumentException" }
Catch [system.exception] { "caught a system.exception" }
Finally { "end of script" }

Just discovered that the errors that are 'caught' when we force
termination with the $erroractionpreference or with the -erroraction
parameter are of type
System.Management.Automation.ActionPreferenceStopException, and not what
Try { Get-ItemProperty -Path "HKCU:\Control Panel\Desktop\" -Name Wallpaper2 }
Catch [System.Management.Automation.ActionPreferenceStopExecution] {
"caught a StopExecution Exception" }
finally { "end of script" }
Instead of trying to trace the errors through the $error variable I used
the errorvariable parameter in the command, and much to my surprise this
PS # Get-ItemProperty -Path "HKCU:\Control Panel\Desktop\" -Name
Wallpaper2 -ErrorVariable x
Get-ItemProperty : Property Wallpaper2 does not exist at path
HKEY_CURRENT_USER\Control Panel\Desktop\.
At line:1 char:17
+ Get-ItemProperty <<<< -Path "HKCU:\Control Panel\Desktop\" -Name
Wallpaper2 -ErrorVariable x
+ CategoryInfo : InvalidArgument: (Wallpaper2:String)
[Get-ItemProperty], PSArgumentException
System.Management.Automation.PSArgumentException,Microsoft.PowerShell.Commands.GetItemPropertyCommand
PS # $x
Command execution stopped because the preference variable
"ErrorActionPreference" or common parameter is set to Stop: Property
Wallpaper2 does
not exist at path HKEY_CURRENT_USER\Control Panel\Desktop\.
PS # $x.Count
1
PS # $x[0].psobject.typenames
System.Management.Automation.ActionPreferenceStopException
System.Management.Automation.RuntimeException
System.SystemException
System.Exception
System.Object
So there we see the ActionPreferenceStopException, and that it is
derived from the RuntimeException class, which explains the behavior I
posted earlier.
So the lesson, I suppose, is be careful with handling exceptions thrown
by erroraction stop!
--
v(^_^)~Clint
http://outputredirection.blogspot.com
.

[Clint B]

I put a little more effort into getting a good resolution to this
question and posted the results on my blog:

http://outputredirection.blogspot.com/2010/04/powershells-trycatchfinally-and.html

Hope that helps. If you would like any further clarification just say so :)