Pass arg through new shell within script

Question

I'm trying to call a new shell due to a memory leak from a library. When I call the shell, I need to pass an arg (the real code will pass 2 args). After the block of code has executed in the new shell, it needs to return a value. I wrote some test code to reproduce the error:

Function GetLastName
{
    Param ($firstName)

    $lastName = Powershell -firstName $firstName {
        Param ([string]$firstName)
        $lastName = ''
        if ($firstName = 'John')
        {
            $lastName = 'Doe'
            Write-Host "Hello $firstName, your last name is registered as $lastName"
        }
        Write-Host "Last name not found"
        Write-Output $lastName
    }
    Write-Output $lastName
}

Function Main
{
    $firstName = 'John'

    $lastName = GetLastName $firstName

    Write-Host "Your name is $firstName $lastName"
}

Main

The error I get...

Powershell : -firstName : The term '-firstName' is not recognized as the name of
a cmdlet, function, script file, or operable
At C:\Scripts\Tests\test1.ps1:5 char:15
+         $lastName = Powershell -firstName $firstName {
+                     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (-firstName : Th...e, or operable :String) [], RemoteException
    + FullyQualifiedErrorId : NativeCommandError

program. Check the spelling of the name, or if a path was included, verify that
the path is correct and try again.
At line:1 char:1
+ -firstName John -encodedCommand DQAKAAkACQAJAFAAYQByAGEAbQAgACgAWwBzAHQAcgBpAG4A ...
+ ~~~~~~~~~~
    + CategoryInfo          : ObjectNotFound: (-firstName:String) [], CommandNotFoundException
    + FullyQualifiedErrorId : CommandNotFoundException

Can anyone help me how to do this?

Use Start-Job approach. It also provide proper separation for Host stream. — user4003407
– user4003407, Commented Jan 24, 2016 at 18:11
Seems pretty complicated. Can you give an example in the answer section? — Fiddle Freak
– Fiddle Freak, Commented Jan 24, 2016 at 18:42
Please stop putting the language tag in the subject of your questions. — Ansgar Wiechers
– Ansgar Wiechers, Commented Jan 24, 2016 at 18:46

Mathias R. Jessen · Accepted Answer · 2016-01-24 21:44:42Z

2

The syntax for calling powershell.exe to execute a scriptblock from within PowerShell is a bit different:

powershell.exe -command { scriptblock content here } -args "arguments","go","here"

So in your script that should be:

$lastName = powershell -Command {
    Param ([string]$firstName)
    $lastName = ''
    if ($firstName = 'John')
    {
        $lastName = 'Doe'
        Write-Host "Hello $firstName, your last name is registered as $lastName"
    } else {
        Write-Host "Last name not found"
    }
    Write-Output $lastName
} -args $firstName

answered Jan 24, 2016 at 21:44

Mathias R. Jessen

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1 Comment

Fiddle Freak Over a year ago

oh let me test this. Thanks for the reply.

Ansgar Wiechers · Accepted Answer · 2016-01-24 18:56:00Z

1

Split your code into two separate scripts and use one just as a launcher for the second. Something like this:

# launcher.ps1
powershell.exe -File 'C:\path\to\worker.ps1' -FirstName $firstName

# worker.ps1
[CmdletBinding()]
Param($firstName)

$lastName = ''
if ($firstName = 'John') {
    $lastName = 'Doe'
    Write-Host "Hello $firstName, your last name is registered as $lastName"
}
Write-Host "Last name not found"
Write-Output $lastName

Note, however, that from the caller perspective the host output (Write-Host) of the new process is merged into its regular output (Write-Output).

answered Jan 24, 2016 at 18:56

Ansgar Wiechers

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1 Comment

Fiddle Freak Over a year ago

well, I was hoping to keep the code in one file, but it looks like this is the best option. The Start-Job is adding unwanted attributes in the table I create.

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