[powershell] Try/catch does not seem to have an effect

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

This is my solution. When Set-Location fails it throws a non-terminating error which is not seen by the catch block. Adding -ErrorAction Stop is the easiest way around this.

try {
    Set-Location "$YourPath" -ErrorAction Stop;
} catch {
    Write-Host "Exception has been caught";
}

If you want try/catch to work for all errors (not just the terminating errors) you can manually make all errors terminating by setting the ErrorActionPreference.

try {

   $ErrorActionPreference = "Stop"; #Make all errors terminating
   get-item filethatdoesntexist; # normally non-terminating
   write-host "You won't hit me";  
} catch{
   Write-Host "Caught the exception";
   Write-Host $Error[0].Exception;
}finally{
   $ErrorActionPreference = "Continue"; #Reset the error action pref to default
}

Alternatively... you can make your own trycatch function that accepts scriptblocks so that your try catch calls are not as kludge. I have mine return true/false just in case i need to check if there was an error... but it doesnt have to. Also, exception logging is optional, and can be taken care of in the catch, but i found myself always calling the logging function in the catch block, so i added it to the try catch function.

function log([System.String] $text){write-host $text;}

function logException{
    log "Logging current exception.";
    log $Error[0].Exception;
}


function mytrycatch ([System.Management.Automation.ScriptBlock] $try,
                    [System.Management.Automation.ScriptBlock] $catch,
                    [System.Management.Automation.ScriptBlock]  $finally = $({})){



# Make all errors terminating exceptions.
    $ErrorActionPreference = "Stop";

    # Set the trap
    trap [System.Exception]{
        # Log the exception.
        logException;

        # Execute the catch statement
        & $catch;

        # Execute the finally statement
        & $finally

        # There was an exception, return false
        return $false;
    }

    # Execute the scriptblock
    & $try;

    # Execute the finally statement
    & $finally

    # The following statement was hit.. so there were no errors with the scriptblock
    return $true;
}


#execute your own try catch
mytrycatch {
        gi filethatdoesnotexist; #normally non-terminating
        write-host "You won't hit me."
    } {
        Write-Host "Caught the exception";
    }

It is also possible to set the error action preference on individual cmdlets, not just for the whole script. This is done using the parameter ErrorAction (alisa EA) which is available on all cmdlets.

Example

try 
{
 Write-Host $ErrorActionPreference; #Check setting for ErrorAction - the default is normally Continue
 get-item filethatdoesntexist; # Normally generates non-terminating exception so not caught
 write-host "You will hit me as exception from line above is non-terminating";  
 get-item filethatdoesntexist -ErrorAction Stop; #Now ErrorAction parameter with value Stop causes exception to be caught 
 write-host "you won't reach me as exception is now caught";
}
catch
{
 Write-Host "Caught the exception";
 Write-Host $Error[0].Exception;
}

Adding "-EA Stop" solved this for me.

Edit: As stated in the comments, the following solution applies to PowerShell V1 only.

See this blog post on "Technical Adventures of Adam Weigert" for details on how to implement this.

Example usage (copy/paste from Adam Weigert's blog):

Try {
    echo " ::Do some work..."
    echo " ::Try divide by zero: $(0/0)"
} -Catch {
    echo "  ::Cannot handle the error (will rethrow): $_"
    #throw $_
} -Finally {
    echo " ::Cleanup resources..."
}

Otherwise you'll have to use exception trapping.

In my case, it was because I was only catching specific types of exceptions:

try
  {
    get-item -Force -LiteralPath $Path -ErrorAction Stop

    #if file exists
    if ($Path -like '\\*') {$fileType = 'n'}  #Network
    elseif ($Path -like '?:\*') {$fileType = 'l'} #Local
    else {$fileType = 'u'} #Unknown File Type

  }
catch [System.UnauthorizedAccessException] {$fileType = 'i'} #Inaccessible
catch [System.Management.Automation.ItemNotFoundException]{$fileType = 'x'} #Doesn't Exist

Added these to handle additional the exception causing the terminating error, as well as unexpected exceptions

catch [System.Management.Automation.DriveNotFoundException]{$fileType = 'x'} #Doesn't Exist
catch {$fileType='u'} #Unknown