Changing Hyper-V Configs in Powershell from CSV - variables generate errors

Question

I am trying to get a small script together that will change the resources on a series of VM's on a hyper-v host. I need to change the CPU count and the Memory allocation to whatever the variables are imported from the CSV. However, when I try to pull the variable for CPU and Memory, I get a series of errors. But if I change those variables to a number, they work just fine. Any help is greatly appreciated.

$VMList = Import-csv "C:\temp\vmspecs_test.csv"

foreach-object {
$VMName = $VMList.Name
$CPUCount = "4"
$MaxMemory = 1GB*("4")
Stop-VM -Name $VMName -Force
Set-VMProcessor $VMName -Count $CPUCount
Set-VMMemory $VMName -DynamicMemoryEnabled $false -StartupBytes $MaxMemory
Start-VM -Name $VMName
}

However, if I change "$CPUCount = $VMList.NewCPU" (which is just a column in csv with a numeric 4 in it), I get the error

"Set-VMProcessor : Cannot convert 'System.Object[]' to the type 'System.Nullable`1[System.Int64]' required by parameter 'Count'.
Specified method is not supported.
At C:\Users\Administrator\Documents\VirtualMachineResourceModification.ps1:10 char:32

• Set-VMProcessor $VMName -Count $CPUCount
• ~~~~~~~~~
• CategoryInfo : InvalidArgument: (:) [Set-VMProcessor], ParameterBindingException
• FullyQualifiedErrorId : CannotConvertArgument,Microsoft.HyperV.PowerShell.Commands.SetVMProcessor"

And if I change the value of $MaxMemory to $MaxMemory = 1GB*($VMList.MaxMem) OR [int64]$MaxMemory = 1GB*($VMList.MaxMem), it errors with

Method invocation failed because [System.Object[]] does not contain a method named 'op_Multiply'.
At C:\Users\Administrator\Documents\VirtualMachineResourceModification.ps1:8 char:1

• $MaxMemory = 1GB*($VMList.MaxMem)
• ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
• CategoryInfo : InvalidOperation: (op_Multiply:String) [], RuntimeException
• FullyQualifiedErrorId : MethodNotFound

Can anyone please tell me what I am doing wrong? I have tried using a singular Set-VM option and ran into conversion of int32 and int64 errors. I have tried using a byte amount (no mathematical operator for memory, just 4294967296) and it still won't work from csv. I appreciate any help in advance.

Answer 1

The variables inside your foreach are not doing what you think they're doing.
You defined $VMList as a list of virtual machines at the beginning.
In line 4, $VMName is not the name of the currently foreach'd VM, but every single item in the "Name" column of your CSV. That doesn't break lines 7-10 because all of those will accept an array of names. Basically, you are running lines 7-10 for every single virtual machine on every pass of the foreach.
Your changed line breaks because the Count parameter of Set-VMProcessor will not accept a list of numbers. $VMList.NewCPU represents a list of every single item in the "NewCPU" column of your CSV. That's what the 'System.Object[]' part of the error is trying to tell you.
To reference the current item in a foreach loop, use $_. So, line 4 becomes:
$VMName = $_.Name
and your updated line becomes:
$CPUCount = $_.NewCPU

Edited to add:
Also, your foreach does not have an input object, so it doesn't know what to foreach over. You can write the foreach line like this:
ForEach-Object -InputObject $VMList -Process {

Personally, I don't find the $_ syntax particularly legible and prefer to use the language construct foreach instead of the cmdlet. That would look something like:

foreach ($VM in $VMList)
{
Stop-VM $VM.Name
...
Start-VM $VM.Name
}