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PowerShell script header to be as strict as possible and always throw exceptions

Posted by jpluimers on 2019/07/24

This is my default PowerShell script header from now on:

Set-StrictMode -Version Latest
$ErrorActionPreference = 'Stop'
$PSDefaultParameterValues['*:ErrorAction']='Stop'

This might sound like overkill, but it solves these problems:

The above helped me tremendously with for instance [WayBack] powershell – Why does the exception not get me in the catch block? – Stack Overflow:

I’m trying to interrogate some service information. Sometimes the installer of the application fails to correctly install, so the registry does not contain a service entry. I want to find out which installer steps did get executed correctly, even on systems that do not have proper logging in the installer.

If MyService does not exist, the script below does not go to the catch block even though the exception handling documentation suggests a bare catch should be enough:

try {
    $path = 'hklm:\SYSTEM\CurrentControlSet\services\MyService'
    $key = Get-Item $path
    $namevalues = $key | Select-Object -ExpandProperty Property |
        ForEach-Object {
        [PSCustomObject] @{
            Name = $_;
            Value = $key.GetValue($_)
        }
    }
    $namevalues | Format-Table
}
catch {
    $ProgramFilesX86 = [System.Environment]::GetFolderPath("ProgramFilesX86");
    $ProgramFiles = [System.Environment]::GetFolderPath("ProgramFiles");
    Write-Host $ProgramFilesX86
    Write-Host $ProgramFiles
}

Why is that and how should I force it to end up in the catch?

This is what PowerShell outputs:

Get-Item : Cannot find path 'HKLM:\SYSTEM\CurrentControlSet\services\MyService' because it does not exist.
At C:\Users\Developer\...\GetMyServiceInfo.ps1:17 char:12
+     $key = Get-Item $path
+            ~~~~~~~~~~~~~~
    + CategoryInfo          : ObjectNotFound: (HKLM:\SYSTEM\Cu...vices\MyService:String) [Get-Item], ItemNotFoundException
    + FullyQualifiedErrorId : PathNotFound,Microsoft.PowerShell.Commands.GetItemCommand

For which I edited the answer to become this:

Force the error to be terminating:

$key = Get-Item $path -ErrorAction Stop

That way it will throw and catch will get it.

Explanation and links to the official Microsoft documentation:

What is missing there is the link to the $PSDefaultParameterValues documentation at [WayBack] about_Parameters_Default_Values | Microsoft Docs

–jeroen

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