Skip to main content

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.

 

Comments

Popular posts from this blog

How to list all the AD LDS instances on a server

AD LDS allows you to provide directory services to applications that are free of the confines of Active Directory.  To list all the AD LDS instances on a server, follow this procedure: Log into the server in question Open a command prompt. Type dsdbutil and press Enter Type List Instances and press Enter . You will receive a list of the instance name, both the LDAP and SSL port numbers, the location of the database, and its status.

How to run GPResult on a remote client with PowerShell

In the past, to run the GPResult command, you would need to either physically visit this client, have the user do it, or use and RDP connection.  In all cases, this will disrupt the user.  First, you need PowerShell remoting enabled on the target machine.  You can do this via Group Policy . Open PowerShell and type this command. Invoke-Command –ScriptBlock {GPResult /r} –ComputerName <ComputerName> Replace <ComputerName> with the name of the target.  Remember, the target needs to be online and accessible to you.

Error icon when creating a GPO Preference drive map

You may not have an error at all.  Take a look at the drive mapping below. The red triangle is what threw us off.  It is not an error.  It is simply a color representation of the Replace option of the Action field in the properties of the drive mappings. Create action This give you a green triangle. The Create action creates a new mapped drive for users. Replace Action The Replace action gives you a red triangle.  This action will delete and recreate mapped drives for users. The net result of the Replace action is to overwrite all existing settings associated with the mapped drive. If the drive mapping does not exist, then the Replace action creates a new drive mapping. Update Action The Update action will have a yellow triangle. Update will modify settings of an existing mapped drive for users. This action differs from Replace in that it only updates settings defined within the preference item. All other settings remain as configured on the mapped drive. If the