Advanced Windows PowerShell Scripting Video Training

Advanced Windows PowerShell Scripting Video Training
Advanced Windows PowerShell Scripting Video Training

Tuesday, March 8, 2016

Why are Objects so Important?

We are in day 1 of a PowerShell class here in Phoenix.  I’ve been keeping an eye on PowerShell.com and PowerShell.org to try and find questions that we can help with.  Right before we started our topic on saving and retrieving objects from disk, an IT pro asked a question concerning getting and processing information about their virtual machines.

Get-VM | Out-File C:\ps\VMS.txt

$VMs = Get-Content -Path C:\PS\VMS.txt
ForEach ($VM in $VMs)
{
    $VM | Select-Object -Property Name
    Get-VM $VM | Get-DatastoreCluster
}

Do you see the problem here?

The IT Pro is correctly getting his virtual machine objects.  The problem is he is saving them to a text file.  Let’s look at the text file.
PS C:\> Get-Content -Path C:\ps\VMS.txt

Name  State   CPUUsage(%) MemoryAssigned(M) Uptime             Status             Versi
                                                                                  on  
----  -----   ----------- ----------------- ------             ------             -----
CL1   Off     0           0                 00:00:00           Operating normally 7.0 
CL2   Off     0           0                 00:00:00           Operating normally 7.0 
DC    Running 0           1132              1.22:38:46.2550000 Operating normally 6.2 
EX1   Off     0           0                 00:00:00           Operating normally 7.0 
S1    Running 0           512               1.22:38:45.3760000 Operating normally 7.0 
S2    Running 0           512               1.22:38:45.1660000 Operating normally 7.0 
SVR1  Off     0           0                 00:00:00           Operating normally 6.2 
SVR2  Off     0           0                 00:00:00           Operating normally 6.2 
Test1 Off     0           0                 00:00:00           Operating normally 7.0 

It looks just like what you would expect if you executed Get-VM.  Let’s look at the objects produced by Get-VM and Get-Content.
PS C:\> Get-Content -Path C:\ps\VMS.txt |
    Get-Member |
    Select-Object -first 1 -ExpandProperty Typename
System.String

PS C:\> Get-VM |
    Get-Member |
    Select-Object -First 1 -ExpandProperty Typename
Microsoft.HyperV.PowerShell.VirtualMachine

The object types are different.  If you want to save your objects to disk, a text file will not work.  Consider using Export-CliXml.  Yes, I know.  It is harder to read.  If you are not planning on automating a process, go ahead and save it as a text file.  You will then have to manually read it and manually execute your actions. This IT Pro was trying to automate a process.  A text file was not working.  This will:

Get-VM | Export-Clixml -Path c:\ps\Vms.xml

$VMs = Import-Clixml -Path C:\ps\Vms.xml
ForEach ($VM in $VMs)
{
    $VM | Select-Object -Property Name
    #Get-VM $VM | Get-DatastoreCluster
}

You may have noticed that I commented out the Get-VM $VM line.  Well, that is another error in his code, but that is for another time.


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