Parameter interpretation when running jobs

Question

$h = "host1.example.com"
$code = {
  $(Get-WmiObject -Class "Win32_ComputerSystem" -Namespace "root\cimv2" -ComputerName $h)
}
$timeout = 5
$jobstate = $(Wait-Job -Job ($job = $(Start-Job -ScriptBlock $code)) -Timeout $timeout)
$wmicomobj = $(Receive-Job -Job $job)

Why does the codeblock above raise the following error?

Cannot validate argument on parameter 'ComputerName'. The argument is null or
empty. Supply an argument that is not null or empty and then try the command
again.
    + CategoryInfo          : InvalidData: (:) [Get-WmiObject], ParameterBindingValidationException
    + FullyQualifiedErrorId : ParameterArgumentValidationError,Microsoft.PowerShell.Commands.GetWmiObjectCommand
    + PSComputerName        : localhost

I would like to use this to implement a timeout when getting WMI objects for multiple hosts in a loop. But first I need to get the results via job execution.

Ansgar Wiechers · Accepted Answer · 2016-06-23 09:20:57Z

5

Variables defined in the global scope of your script are not available inside the scriptblock unless you use the using qualifier:

$code = {
  Get-WmiObject -Class "Win32_ComputerSystem" -Namespace "root\cimv2" -ComputerName $using:h
}

or pass them in as arguments, like this:

$code = {
  Param($hostname)
  Get-WmiObject -Class "Win32_ComputerSystem" -Namespace "root\cimv2" -ComputerName $hostname
}
$jobstate = Wait-Job -Job ($job = $(Start-Job -ScriptBlock $code -ArgumentList $h)) -Timeout $timeout

or like this:

$code = {
  Get-WmiObject -Class "Win32_ComputerSystem" -Namespace "root\cimv2" -ComputerName $args[0]
}
$jobstate = Wait-Job -Job ($job = $(Start-Job -ScriptBlock $code -ArgumentList $h)) -Timeout $timeout

answered Jun 23, 2016 at 9:20

Ansgar Wiechers

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