PowerShell Invoke-Command not passing parameters properly

Question

I have a PowerShell Script that will invoke a command on a remote server. I'm trying to set this script up so that I can pass in a service parameter and it will drop that specific table in MongoDB

$service = "DatabaseName"

$username = "username"
$password = "password"

$pass = ConvertTo-SecureString -AsPlainText $password -Force
$cred = New-Object System.Management.Automation.PSCredential -ArgumentList $username, $pass

Invoke-Command -ComputerName Remote-Server1 -Credential $cred -ArgumentList $service -ScriptBlock {
    param($service) 
    & 'C:\Program Files\MongoDB\Server\4.0\bin\mongo.exe' $service --eval 'db.dropDatabase()'
}

Invoke-Command -ComputerName Remote-Server2 -Credential $cred -ArgumentList $service -ScriptBlock {
    param($service) 
    & 'C:\Program Files\MongoDB\Server\4.0\bin\mongo.exe' $service --eval 'db.dropDatabase()'
}

If I were to use the following it does not drop the MongoDB database:

& 'C:\Program Files\MongoDB\Server\4.0\bin\mongo.exe' $service --eval 'db.dropDatabase()'

However, If I use the following it works as expected:

& 'C:\Program Files\MongoDB\Server\4.0\bin\mongo.exe' DatabaseName --eval 'db.dropDatabase()'

Why does it work when I hard code that database name but not when I use a variable.

Moerwald · Accepted Answer · 2019-07-16 09:39:40Z

Since your code only needs $service in a read-only manner you can use the Using:-scope modifier, see additional information here.

Based on that you can change the code to:

$service = "DatabaseName"
$username = "username"
$password = "password"

$pass = ConvertTo-SecureString -AsPlainText $password -Force
$cred = New-Object System.Management.Automation.PSCredential -ArgumentList $username, $pass

Invoke-Command -ComputerName Remote-Server1 -Credential $cred -ArgumentList $service -ScriptBlock {
    & 'C:\Program Files\MongoDB\Server\4.0\bin\mongo.exe' $Using:service --eval 'db.dropDatabase()'
}

Invoke-Command -ComputerName Remote-Server2 -Credential $cred -ArgumentList $service -ScriptBlock {
    & 'C:\Program Files\MongoDB\Server\4.0\bin\mongo.exe' $Using:service --eval 'db.dropDatabase()'
}

When performing remote commands via Invoke-Command I either use the Using modifier of prefix the variables in the param block with remote. Based on that I can avoid "unwanted" behaviors (as the one you stated above).

So another alternative would be:

Invoke-Command -ComputerName Remote-Server1 -Credential $cred -ArgumentList $service -ScriptBlock {
    param($remoteService)
    & 'C:\Program Files\MongoDB\Server\4.0\bin\mongo.exe' $remoteService --eval 'db.dropDatabase()'
}

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