PowerShell try/catch/finally

Question

I recently wrote a PowerShell script that works great - however, I'd like to now upgrade the script and add some error checking / handling - but I've been stumped at the first hurdle it seems. Why won't the following code work?

try {   Remove-Item "C:\somenonexistentfolder\file.txt" -ErrorAction Stop }  catch [System.Management.Automation.ItemNotFoundException] {   "item not found" }  catch {   "any other undefined errors"   $error[0] }  finally {   "Finished" } 

The error is caught in the second catch block - you can see the output from $error[0]. Obviously I would like to catch it in the first block. What am I missing?

Answer 1

-ErrorAction Stop is changing things for you. Try adding this and see what you get:

Catch [System.Management.Automation.ActionPreferenceStopException] { "caught a StopExecution Exception"  $error[0] } 

Answer 2

That is very odd.

I went through ItemNotFoundException's base classes and tested the following multiple catches to see what would catch it:

try {   remove-item C:\nonexistent\file.txt -erroraction stop } catch [System.Management.Automation.ItemNotFoundException] {   write-host 'ItemNotFound' } catch [System.Management.Automation.SessionStateException] {   write-host 'SessionState' } catch [System.Management.Automation.RuntimeException] {   write-host 'RuntimeException' } catch [System.SystemException] {   write-host 'SystemException' } catch [System.Exception] {   write-host 'Exception' } catch {   write-host 'well, darn' } 

As it turns out, the output was 'RuntimeException'. I also tried it with a different exception CommandNotFoundException:

try {   do-nonexistent-command } catch [System.Management.Automation.CommandNotFoundException] {   write-host 'CommandNotFoundException' } catch {   write-host 'well, darn' } 

That output 'CommandNotFoundException' correctly.

I vaguely remember reading elsewhere (though I couldn't find it again) of problems with this. In such cases where exception filtering didn't work correctly, they would catch the closest Type they could and then use a switch. The following just catches Exception instead of RuntimeException, but is the switch equivalent of my first example that checks all base types of ItemNotFoundException:

try {   Remove-Item C:\nonexistent\file.txt -ErrorAction Stop } catch [System.Exception] {   switch($_.Exception.GetType().FullName) {     'System.Management.Automation.ItemNotFoundException' {       write-host 'ItemNotFound'     }     'System.Management.Automation.SessionStateException' {       write-host 'SessionState'     }     'System.Management.Automation.RuntimeException' {       write-host 'RuntimeException'     }     'System.SystemException' {       write-host 'SystemException'     }     'System.Exception' {       write-host 'Exception'     }     default {'well, darn'}   } } 

This writes 'ItemNotFound', as it should.