Try/catch does not seem to have an effect

Question

I am new to powershell, and I am trying to add error handling via try/catch statements, but they don't seem to actually be catching the error. This is powershell v2 CP3.

$objComputer = $objResult.Properties; $strComputerName = $objComputer.name write-host "Checking machine: " $strComputerName  try {     $colItems = get-wmiobject -class "Win32_PhysicalMemory" -namespace "root\CIMV2" -computername $strComputerName -Credential $credentials     foreach ($objItem in $colItems)      {         write-host "Bank Label: " $objItem.BankLabel         write-host "Capacity: " ($objItem.Capacity / 1024 / 1024)         write-host "Caption: " $objItem.Caption         write-host "Creation Class Name: " $objItem.CreationClassName               write-host     } } Catch  {     write-host "Failed to get data from machine (Error:"  $_.Exception.Message ")"     write-host } finally  { }   

When it fails to contact a specific machine, I get this in console, and not my clean catch message:

Get-WmiObject : The RPC server is
unavailable. (Exception from HRESULT:
0x800706BA) At Z:\7.0 Intern
Programvare\Powershell\Get memory of
all computers in AD.ps1:25 char:34
+ $colItems = get-wmiobject <<<< -class "Win32_PhysicalMemory"
-namespace "root\CIMV2" -computername $strComputerName -Credential
$credentials
+ CategoryInfo : InvalidOperation: (:) [Get-WmiObject],
COMException
+ FullyQualifiedErrorId : GetWMICOMException,Microsoft.PowerShell.Commands.GetWmiObjectCommand

Answer 1

I was able to duplicate your result when trying to run a remote WMI query. The exception thrown is not caught by the Try/Catch, nor will a Trap catch it, since it is not a "terminating error". In PowerShell, there are terminating errors and non-terminating errors . It appears that Try/Catch/Finally and Trap only works with terminating errors.

It is logged to the $error automatic variable and you can test for these type of non-terminating errors by looking at the $? automatic variable, which will let you know if the last operation succeeded ($true) or failed ($false).

From the appearance of the error generated, it appears that the error is returned and not wrapped in a catchable exception. Below is a trace of the error generated.

PS C:\scripts\PowerShell> Trace-Command -Name errorrecord  -Expression {Get-WmiObject win32_bios -ComputerName HostThatIsNotThere}  -PSHost DEBUG: InternalCommand Information: 0 :  Constructor Enter Ctor Microsoft.PowerShell.Commands.GetWmiObjectCommand: 25857563 DEBUG: InternalCommand Information: 0 :  Constructor Leave Ctor Microsoft.PowerShell.Commands.GetWmiObjectCommand: 25857563 DEBUG: ErrorRecord Information: 0 :  Constructor Enter Ctor System.Management.Automation.ErrorRecord: 19621801 exception = System.Runtime.InteropServices.COMException (0x800706BA): The RPC server is unavailable. (Exception from HRESULT: 0x800706BA)    at System.Runtime.InteropServices.Marshal.ThrowExceptionForHRInternal(Int32 errorCode, IntPtr errorInfo)    at System.Management.ManagementScope.InitializeGuts(Object o)    at System.Management.ManagementScope.Initialize()    at System.Management.ManagementObjectSearcher.Initialize()    at System.Management.ManagementObjectSearcher.Get()    at Microsoft.PowerShell.Commands.GetWmiObjectCommand.BeginProcessing() errorId = GetWMICOMException errorCategory = InvalidOperation targetObject = DEBUG: ErrorRecord Information: 0 :  Constructor Leave Ctor System.Management.Automation.ErrorRecord: 19621801 

A work around for your code could be:

try {     $colItems = get-wmiobject -class "Win32_PhysicalMemory" -namespace "root\CIMV2" -computername $strComputerName -Credential $credentials     if ($?)     {       foreach ($objItem in $colItems)        {           write-host "Bank Label: " $objItem.BankLabel           write-host "Capacity: " ($objItem.Capacity / 1024 / 1024)           write-host "Caption: " $objItem.Caption           write-host "Creation Class Name: " $objItem.CreationClassName                 write-host       }     }     else     {        throw $error[0].Exception     }