How to handle failed variable assignments in powershell?

Question

I am trying to handle setting a PowerShell variable from a registry key.

So I use a try{} catch {} to get rid of eventual errors in case the key doesn't exists. However, I still get the error output on console.

$ZZ_ConVTL = try { (Get-ItemProperty -path "HKCU:\Console" -name VirtualTerminalLevel).VirtualTerminalLevel } catch { "N/A" }

...

# Output:
Get-ItemProperty : Property VirtualTerminalLevel does not exist at path HKEY_CURRENT_USER\Console.
At C:\Users\Administrator\Documents\xxxx\xxxx.ps1:181 char:32
+ ...    = try { (Get-ItemProperty -path "HKCU:\Console" -name VirtualTermi ...
+                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidArgument: (VirtualTerminalLevel:String) [Get-ItemProperty], PSArgumentException
    + FullyQualifiedErrorId : System.Management.Automation.PSArgumentException,Microsoft.PowerShell.Commands.GetItemPropertyCommand

How can I handle and avoid this error from showing up in the console?

Answer 1

What your Get-ItemProperty call emits is a non-terminating error, whereas try / catch only catches terminating errors.

• Non-terminating errors are far more common that terminating ones.

Use common parameter -ErrorAction Stop to promote (the first) non-terminating error generated by a cmdlet to a terminating one that try / catch handles.

You can generally achieve the same effect by setting preference variable
$ErrorActionPreference = 'Stop' beforehand, but note that doing so has no effect on functions implemented in script modules.

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See also:

• The about_Try_Catch_Finally help topic.

• A description of the fundamental error types in the context of guidance for command authors on when to emit a terminating vs. a non-terminating error: this answer.

• A comprehensive overview of PowerShell's surprisingly complex error handling: this GitHub docs issue.