playing with jobs

I was playing with some little code and found a moment I cannot understand

$w = ‘1…10’
Invoke-Expression $w #this runs OK

then I try to run it as a job

start-job {Invoke-Expression $w} # or start-job {Invoke-Expression $global:w}

this returns an error: Cannot evaluate parameter ‘Command’ because its argument is specified as a script block and there is no input. A script block cannot be evaluated without input.

what is wrong?

Hi Simeon,

You will need to use the $using: scope modifier to let the PowerShell engine know to inject the value of the variable $w into the scriptblock {}.

$w = '1..10' Start-Job { Invoke-Expression $using:w }

Jobs are running in another process and do not have access to variables in your current session.

Please consider more then twice if Invoke-Expression is the right command to be included in your scripts. It is a dangerous / harmful command because it allows injection of bad command lines similar to SQL injection and its usage can be avoided in 99.9% of all use cases.


The problem is that that a job runs in a separate Powershell process so in your case $w doesn’t exist when Invoke-expression tries to run

You could do this

Start-Job -ScriptBlock { $w = ‘1…10’; Invoke-Expression $w}

$w = ‘1…10’
Start-Job -ScriptBlock { param($w) Invoke-Expression $w} -ArgumentList $w

thanks, now I got it