Cannot bind parameter to argument 'command' because it is null. Powershell

powershell start-job
srikanth peetha picture srikanth peetha · Jul 27, 2017 · Viewed 9.1k times · Source

I had a function similar to below code. It receives command and the command arguments. I had to run this command in background and collect the output. But that last statement is bugging me with this error

Error:

Cannot bind argument to parameter 'Command' because it is null.
+ CategoryInfo          : InvalidData: (:) [Invoke-Expression], ParameterBindingValidationException
+ FullyQualifiedErrorId : ParameterArgumentValidationErrorNullNotAllowed,Microsoft.PowerShell.Commands.InvokeExpre
ssionCommand
+ PSComputerName        : localhost

Code:

$cmd = 'Get-content'
$Arg = 'path to file'
$sb = "$cmd $Arg -ErrorVariable e -ErrorAction Stop"
invoke-Expression $sb #This printsoutput
$job = Start-job -ScriptBlock {Invoke-Expression $sb}
wait-job -id $job.Id
$job | Receive-job #this should print output but throwing error

I am pretty sure last line is the one throwing the error.

Answer

BenH picture BenH · Jul 27, 2017

Another alternative to get the $sb into the scope of the scriptblock besides -argumentlist is to use the $using: scope. (PowerShell 3+)

$cmd = 'Get-content'
$Arg = 'path to file'
$sb = "$cmd $Arg -ErrorVariable e -ErrorAction Stop"
$job = Start-job -ScriptBlock {Invoke-Expression $using:sb}
wait-job -id $job.Id
$job | Receive-job

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