How to catch Exceptions with PowerShell

Question

I am getting this error.

Get-WmiObject : The RPC server is unavailable. (Exception from HRESULT: 0x800706BA)
At F:\Code\powershell\network_shutdown\TurnNetworkOff.ps1:19 char:26
+             Get-WmiObject <<<<  -computername $computer Win32_NetworkAdapter -filter "AdapterTypeId
=0" | % {
    + CategoryInfo          : InvalidOperation: (:) [Get-WmiObject], COMException
    + FullyQualifiedErrorId : GetWMICOMException,Microsoft.PowerShell.Commands.GetWmiObjectCommand

Here is my code

#Define variables used in this script
$namespace = "root\WMI"

$array = @()
$exceptionarray = @()

$computerlist = Get-Content F:\Code\powershell\network_shutdown\computer-list.csv

foreach ($computer in $computerlist) 
{
    # Main Processing Section
    # Write-Host $computer
    if((Test-Connection -Cn $computer -BufferSize 16 -Count 1 -ea 0 -quiet))
    {
        Try
        {
            #Write-Host $computer
            #Write-Host "Disable `"Allow the computer to turn off this device to save power`""
            Get-WmiObject -computername $computer Win32_NetworkAdapter -filter "AdapterTypeId=0" | % {
                $strNetworkAdapterID=$_.PNPDeviceID.ToUpper()
                Get-WmiObject -class MSPower_DeviceEnable -computername $computer -Namespace $namespace | % {
                    if($_.InstanceName.ToUpper().startsWith($strNetworkAdapterID))
                    {
                        $_.Enable = $false
                        $_.Put() | Out-Null
                    }
                }
            }

            #Write-Host "Disable `"Allow this device to wake the computer`""
            Get-WmiObject -computername $computer Win32_NetworkAdapter -filter "AdapterTypeId=0" | % {
                $strNetworkAdapterID=$_.PNPDeviceID.ToUpper()
                Get-WmiObject -class MSPower_DeviceWakeEnable -computername $computer -Namespace $namespace | % {
                    if($_.InstanceName.ToUpper().startsWith($strNetworkAdapterID)){
                        $_.Enable = $false
                        $_.Put() | Out-Null
                    }
                }
            }

            #Write-Host "Disable `"Only allow a magic packet to wake the computer`""
            Get-WmiObject -computername $computer Win32_NetworkAdapter -filter "AdapterTypeId=0" | % {
                $strNetworkAdapterID=$_.PNPDeviceID.ToUpper()
                Get-WmiObject -class MSNdis_DeviceWakeOnMagicPacketOnly -computername $computer -Namespace $namespace | % {
                    if($_.InstanceName.ToUpper().startsWith($strNetworkAdapterID)){
                        $_.EnableWakeOnMagicPacketOnly = $false
                        $_.Put() | Out-Null
                    }
                }
            }
        } Catch [Exception]
        {
            Write-Host $computer + " WMIC ERROR"
            if ($_.Exception.GetType().Name -eq "COMException") {
                Write-Host $computer + " WMIC ERROR"
            }

            $output = new-object psobject
            $output | Add-Member noteproperty PCTag $computer

            [PSObject[]]$exceptionarray += $output
        }        
    } else {
        Write-Host $computer + " OFFLINE"
        $output = new-object psobject
        $output | Add-Member noteproperty PCTag $computer

        [PSObject[]]$array += $output
    }

    $array | Export-Csv -Path F:\Code\powershell\network_shutdown\ResultsOffline.csv
    $exceptionarray | Export-Csv -Path F:\Code\powershell\network_shutdown\ResultsException.csv
}

Solution

The GetWMICOMException is a non-terminating error, meaning that with a default $ErrorActionPreference of Continue, the code in the try block is going to continue its execution after writing out the exception as an error

Enclose the Get-WmiObject call with a try-catch block, but make sure that the -ErrorAction is set to Stop:

# Try-Catch block starts
try 
{
    # Call Get-WmiObject
    Get-WmiObject -ComputerName $computer -Class "Win32_NetworkAdapter" -ErrorAction Stop
}
# If an Exception of the type COMException is thrown, execute this block
catch [System.Runtime.InteropServices.COMException]
{
    # You can inspect the error code to see what specific error we're dealing with 
    if($_.Exception.ErrorCode -eq 0x800706BA)
    {
        # This is instead of the "RPC Server Unavailable" error
        Write-Error -Message "Your own custom message" 
    }
    else
    {
        Write-Error -Message "Some other COMException was thrown"
    }
}
# If any other type of Exception is thrown, execute this block
catch [System.Exception]
{
    Write-Error -Message "Some other exception that's nothing like the above examples"
}
# When all of the above has executed, this block will execute
finally
{
    Write-Verbose "Get-WmiObject object was executed"
}

Alternatively, you could set the $ErrorActionPreference to Stop before executing your script:

# Before the rest of the script
$ErrorActionPreference = Stop

For more help about the try-catch-finally construction:

Get-Help about_Try_Catch_Finally -Full

For more help about the $*Preference vars:

Get-Help about_Preference_variables -Full

Comments

[software is fun]

@vjones I saw that. Isn't that what Im doing in my code? The only difference is that my Exceptions aren't being caught. This could be a possible coding error, syntax error or logic error. I am unable to find the issue. That's why I posted it here

[user24313]

Just to add another resource on Powershell error handling, check out the eBook available on powershell.org. They have a small library of useful books written by key community members and they can be a good place to jump off from. powershell.org/wp/ebooks