Error Handling

Utilize -ErrorAction Stop with Cmdlets

When handling errors, use the -ErrorAction Stop parameter on cmdlets to ensure that errors generate terminating exceptions, which can be trapped and handled effectively.

Set $ErrorActionPreference for Non-Cmdlets

For non-cmdlet commands, set $ErrorActionPreference = 'Stop' before execution and reset it to 'Continue' afterwards. If you're worried about using -ErrorAction because it might terminate the entire pipeline, reconsider the pipeline's complexity. Opt for a more script-based approach, as it allows for better automated error handling.

Commands or code that might fail should handle a single task, such as querying one computer, deleting one file, or updating one user. This way, if an error occurs, you can manage it and proceed with the next task.

Avoid Using Flags for Error Handling

Avoid using flags to handle errors:

try {
    $continue = $true
    Do-Something -ErrorAction Stop
} catch {
    $continue = $false
}

if ($continue) {
    Do-This
    Set-That
    Get-Those
}

Instead, encapsulate the entire operation within the try block:

try {
    Do-Something -ErrorAction Stop
    Do-This
    Set-That
    Get-Those
} catch {
    Handle-Error
}

This approach makes the logic easier to follow.

Avoid Using $?

When examining errors, avoid using $?. This variable only indicates whether the last command considered itself successful, without providing error details.

Refrain from Testing for Null Variables as Error Conditions

Avoid using null variable checks as an error condition:

$user = Get-ADUser -Identity Bob

if ($user) {
    $user | Do-Something
} else {
    Write-Warning "Could not get user $user"
}

While sometimes necessary, especially if the command won't produce a trappable exception, this method can make debugging more complex.

Copy $Error[0] to Your Own Variable

Within a catch block, use $_ or $Error[0] to access the last error. Immediately copy this information into your own variable, as subsequent commands can overwrite $_ or change $Error[0]. It's usually unnecessary to clear $Error since PowerShell maintains this collection automatically.