Advanced Windows PowerShell Scripting Video Training

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Advanced Windows PowerShell Scripting Video Training

Wednesday, October 10, 2012

Expanding Custom ErrorVariable usage in PowerShell

Using the PowerShell common parameter –ErrorVariable allows you to capture the error that a cmdlet has produced so you can work with it. Take a look at the following code:

$Computers = "NotOnline"

ForEach ($Computer in $Computers)

{

    Get-WmiObject Win32_OperatingSystem -ComputerName $Computers -ErrorVariable +MyErrors

    Get-Service -ComputerName $Computer -ErrorVariable +MyErrors

    Get-Content -Path c:\DoesNotExists.txt -ErrorVariable +MyErrors

}

If we look at the $MyError variable, we receive the same information that is displayed on the screen:

$MyErrors

Get-Content : Cannot find path 'C:\DoesNotExists.txt' because it does not exist.

At line:6 char:5

+     Get-Content -Path c:\DoesNotExists.txt -ErrorVariable MyErrors

+     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    + CategoryInfo          : ObjectNotFound: (C:\DoesNotExists.txt:String) [Get-Content]

   , ItemNotFoundException

    + FullyQualifiedErrorId : PathNotFound,Microsoft.PowerShell.Commands.GetContentComman

   d

What about when we use code like this in which we want to reuse the error variable?

$Computers = "NotOnline"

ForEach ($Computer in $Computers)

{

    Get-WmiObject Win32_OperatingSystem -ComputerName $Computers -ErrorVariable MyErrors

    Get-Service -ComputerName $Computer -ErrorVariable MyErrors

    Get-Content -Path c:\DoesNotExists.txt -ErrorVariable MyErrors

}

 

 

This is what is contained inside the $MyErrors variable:

$MyErrors

Get-Content : Cannot find path 'C:\DoesNotExists.txt' because it does not exist.

At line:6 char:5

+     Get-Content -Path c:\DoesNotExists.txt -ErrorVariable MyErrors

+     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    + CategoryInfo          : ObjectNotFound: (C:\DoesNotExists.txt:String) [Get-Content]

   , ItemNotFoundException

    + FullyQualifiedErrorId : PathNotFound,Microsoft.PowerShell.Commands.GetContentComman

   d

 

Only one error remains.

 

In other words, you would have to write code to take a look at each error and decide what to do then.  This may not be suitable for your code.  You could turn your custom error variable into an array. You can do this by adding the  +’ character in front of your custom variable.  See below:

 

$Computers = "NotOnline"

ForEach ($Computer in $Computers)

{

    Get-WmiObject Win32_OperatingSystem -ComputerName $Computers -ErrorVariable +MyErrors

    Get-Service -ComputerName $Computer -ErrorVariable +MyErrors

    Get-Content -Path c:\DoesNotExists.txt -ErrorVariable +MyErrors

}

 

 

Now here is the output of $MyErrors:

PS C:\Users\Jason> $MyErrors

Get-Content : Cannot find path 'C:\DoesNotExists.txt' because it does not exist.

At line:6 char:5

+     Get-Content -Path c:\DoesNotExists.txt -ErrorVariable MyErrors

+     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    + CategoryInfo          : ObjectNotFound: (C:\DoesNotExists.txt:String) [Get-Content]

   , ItemNotFoundException

    + FullyQualifiedErrorId : PathNotFound,Microsoft.PowerShell.Commands.GetContentComman

   d

 

Get-WmiObject : The RPC server is unavailable. (Exception from HRESULT: 0x800706BA)

At line:4 char:5

+     Get-WmiObject Win32_OperatingSystem -ComputerName $Computers -ErrorVariable  ...

+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    + CategoryInfo          : InvalidOperation: (:) [Get-WmiObject], COMException

    + FullyQualifiedErrorId : GetWMICOMException,Microsoft.PowerShell.Commands.GetWmiObje

   ctCommand

 

Cannot open Service Control Manager on computer 'NotOnline'. This operation might require

other privileges.

Get-Content : Cannot find path 'C:\DoesNotExists.txt' because it does not exist.

At line:6 char:5

+     Get-Content -Path c:\DoesNotExists.txt -ErrorVariable +MyErrors

+     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    + CategoryInfo          : ObjectNotFound: (C:\DoesNotExists.txt:String) [Get-Content]

   , ItemNotFoundException

    + FullyQualifiedErrorId : PathNotFound,Microsoft.PowerShell.Commands.GetContentComman

   d

 

You can see that it contains all the errors. Your variable is now an array.  You can get the count information of how many cells are in the array.

$MyErrors.count

4

 

You can also access the array via index number.

$MyErrors[1]

Get-WmiObject : The RPC server is unavailable. (Exception from HRESULT: 0x800706BA)

At line:4 char:5

+     Get-WmiObject Win32_OperatingSystem -ComputerName $Computers -ErrorVariable  ...

+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    + CategoryInfo          : InvalidOperation: (:) [Get-WmiObject], COMException

    + FullyQualifiedErrorId : GetWMICOMException,Microsoft.PowerShell.Commands.GetWmiObje

   ctCommand

 

The custom error variable will continue to append new data to it until you send data to it without the ‘+’ character.  For that reason, the first time you use it in your script, you may want to omit the ‘+’ character so you clear the array each time the script is ran in your current PowerShell session.

 

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