How to determine success of ScriptBlock? - powershell

Question

I want to know if a ScriptBlock executed successfully.
If I run
1/0; echo $?
I get
RuntimeException: Attempted to divide by zero.
false
but if I do
$s = { 1/0 }; Invoke-Command $s; echo $?
I get
RuntimeException: Attempted to divide by zero.
true
I assume that $? is referring to the execution of Invoke-Command, but how can I get success of the script block itself?
I don't need to use Invoke-Command, if changing to $s.Invoke() is viable then happily use that.
Context
I want to write a function for a DSL along the likes of
function at_place {
Param(
[string] $Path,
[scriptblock] $ScriptBlock
)
Push-Location $Path ;
Invoke-Command $ScriptBlock ;
# following line doesn't work
[bool] $ScriptBlockPass = $? ;
If ( $? ){
Write-Debug "success!" ;
Pop-Location ;
} Else {
Write-Error "ScriptBlock failed, remaining at $Path, please fix manually." ;
throw "ScriptBlock failed at $Path" ;
}
}
I have things in my buffer like
Push-Location ~/foo; doStuff; If ( $? ){ Pop-Location; } Else { Write-Error "Failed, fix here" }
Which I would like to write as
at_place ~/foo { doStuff; }
My actual change is about using Git to ignore a bunch of files, stash them, apply some edits, and then reignore them etc. Simplified here hopefully to be more broadly applicable and less distracting.

Answer 1

Your question is a bit broad and the answer is, it really depends.
Child scope invocations can only update the value of $? via $PSCmdlet using either .WriteError method or .ThrowTerminatingError method as stated in the about Automatic Variables documentation. This would imply that the script block or function is an advanced one:
$s = {
[CmdletBinding()]
param()
try {
1 / 0
}
catch {
$PSCmdlet.WriteError($_)
}
}
& $s # Writes Error
$? # Value will be False (Failure)
For a non-advanced function or script block, $? would be categorized as unreliable, one way to know if the script block succeeded (and by succeeded I mean it had no errors) and, in my opinion, the most reliable one, would be to set the error preference to Stop to target both, terminating an non terminating errors and execute the script block in a try / catch / finally:
$s = { Write-Error foo }
try {
$previousPreference = $ErrorActionPreference
$ErrorActionPreference = 'Stop'
& $s
}
catch {
'had errors'
}
finally {
$ErrorActionPreference = $previousPreference
}
As for the new edit, I would approach your function this way:
function at_place {
[CmdletBinding()]
Param(
[string] $Path,
[scriptblock] $ScriptBlock
)
try {
$sbSuccess = $true
$ErrorActionPreference = 'Stop'
$pushSuccess = Push-Location $Path -PassThru
& $ScriptBlock
}
catch {
$sbSuccess = $false
$PSCmdlet.ThrowTerminatingError($_)
}
finally {
if($pushSuccess -and $sbSuccess) {
Pop-Location
}
}
}