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

Question

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 1

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

Answer 2

The issue here is that you are not actually giving Invoke-Expression a command.
Whenever you create a new context ( in this case, a job ) you loose your access to the parent session's environment. In your case $sb is currently null.
The way that you manage this is to pass the values as arguments via the -ArgumentList parameter of Start-Job:
start-job -ScriptBlock {} -ArgumentList
In order to facilitate handing $sb to the ScriptBlock you would do this:
$sb = "$cmd $Arg -ErrorVariable e -ErrorAction Stop"
$job = start-job -ScriptBlock { Param([string]$sb)
Invoke-Expression $sb
} -ArgumentList $sb
This can be confusing so this is the same code written with more friendly names:
$OuterSB = "$cmd $Arg -ErrorVariable e -ErrorAction Stop"
$job = start-job -ScriptBlock { Param([string]$InnerSB)
Invoke-Expression $InnerSB
} -ArgumentList $OuterSB

Answer 3

I got the same error but when I run PowerShell using administrator privileges, I don't get this error. Good luck!

Answer 4

I also got the same error when running command with user without proper authorizations.
This in deed can be related to that.
For example my code:
$allParams = #(10, "Some Process")
Start-Job -ScriptBlock $restartProcessRobot -ArgumentList $allParams
<#
#descr
Function that restarts given proces -DisplayName after given number of seconds.
#param1 Integer number of seconds after which the process should be restarted.
#param2 String display name of process(es) that must be affected. Wild cards accepted.
#>
$restartServiceAfter = {
param($seconds, $processName)
Start-Sleep $seconds
Restart-Service -DisplayName $processName -Force
}
And user is not authorized to restart services.