$_.Exception is $null when used in a call – why? [duplicate]

Question

I have a PowerShell script containing the following logging function:

function LogError([string] $message, $exception = $null) {…}

In a try-catch block, when an exception occurs, I call that logging function like this:

catch { LogError("…", $_.Exception) }

In the LogError function, the second argument is always $null. Why?

I couldn't find any documentation that would explain why I cannot use $_.Exception in a function call or that I am supposed to use instead.

This is a common mistake. In PowerShell you do not call functions the way you would in other languages Function(Args) The parens are precedence and grouping operators so when you pass your args like this you are passing a single array with 2 elements instead of 2 discrete arguments. — Steven
– Steven, Commented Jun 22, 2022 at 14:28
PowerShell Gotcha 2. parentheses and commas are not used with arguments — iRon
– iRon, Commented Jun 22, 2022 at 14:34

Sage Pourpre · Accepted Answer · 2022-06-22 14:47:52Z

3

Powershell function arguments are not passed using the parenthesis / comma formatting.

That is bad

LogError("…", $_.Exception)

Powershell take that as a single array argument. This is actually the same as LogError -Message ("...",$_.Exception)

That is ok

LogError '…' $_.Exception

That is best

 LogError -message '...' -exception $_.Exception

Complete working example

function LogError([string] $message, $exception = $null) { Write-Host $message $exception | Out-String | Write-Host -ForegroundColor red } try { throw 'Noooo !!!!' } catch { LogError -message 'oops' -exception $_.Exception }

edited Jun 22, 2022 at 14:47

answered Jun 22, 2022 at 14:20

Sage Pourpre

10.4k3 gold badges30 silver badges43 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

Steven Over a year ago

I'd advise not to use $_ in a catch block. $_ is used all over PowerShell so there can be conflicts. For example if you use a try catch within a ForEach-Object which $_ are you exposing. If you just caught an error it should be the last error, you can use $Error[0].Exception instead...

AxD Over a year ago

@Steven: Great suggestion! I'm actually editing an existing PowerShell script. Don't want to alter it too much. I got distracted by the existing code, not recognizing it was wrong.

Sage Pourpre Over a year ago

@Steven f you use a try catch within a ForEach-Object, the $_ should always be set to the error within the catch block because it is the closest element to it. At that time, that automatic variable will always contain the error. That's a problem only when you have multiple layer of $_ and you need to access an outer layer (then it is not accessible via $_ at that time). I prefer $_ for brevity but both are indeed equivalent.

Steven Over a year ago

@SagePourpre It's only a practical suggestion. While you're correct you lose the ability to reference the current pipeline element in a ForEach-Object scenario. I don't know if the disadvantages stop there. I suppose it could also be an issue in a function process block, although best practice there is to use the parameter variable instead of $_.

Collectives™ on Stack Overflow

$_.Exception is $null when used in a call – why? [duplicate]

1 Answer 1

4 Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

4 Comments

Linked

Related