How to catch exceptions in PowerShell?

Question

If I have a piece of code that throws an exception I get an error message, but I have no idea how to correctly catch (or determine) the exception that is being thrown. Normally I'll just catch System.Exception which is a bad idea.

Here is an example... I'm trying to create a folder on a drive that doesn't exist:

PS <dir> .\myScript.ps1 z:\test
mkdir : Cannot find drive. A drive with the name 'z' does not exist.
At <dir>myScript.ps1:218 char:7
+       mkdir $args[0] 1> $null
+       ~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : ObjectNotFound: (z:String) [New-Item], DriveNotFoundExc
   eption
    + FullyQualifiedErrorId : DriveNotFound,Microsoft.PowerShell.Commands.NewItemComm
   and

I've tried catching System.DriveNotFoundException, but rerunning my script still produces the uncaught exception.

Are there any tips as to effectively handling any type of exception?

Answer 1

Right after running the command inspect the contents of $error[0]. Look at the Exception property e.g.:

$error[0] | fl * -force

writeErrorStream      : True
PSMessageDetails      :
Exception             : System.Management.Automation.DriveNotFoundException: Cannot find drive. A drive with the name
                        'z' does not exist.
                           at System.Management.Automation.SessionStateInternal.GetDrive(String name, Boolean
                        automount)
                           at System.Management.Automation.SessionStateInternal.GetDrive(String name, Boolean

That particular exception would be [System.Management.Automation.DriveNotFoundException].

BTW if you want to "catch" that exception, you will need to convert the non-terminating error into a terminating error using -EA Stop in order for it to generate an exception that you can catch e.g.:

PS> try {mkdir z:\foo -ea Stop} catch {$_.Exception.GetType().FUllname}
System.Management.Automation.DriveNotFoundException