Prof. Powershell

To Err[or] is Human

And to use the -ErrorVariable cmdlet to keep track of them is divine.

• By Jeffery Hicks
• 10/01/2008

PS C:\> $error[0]

But there may be times when you want to save the error information within a command. Perhaps you want to log it to a text file or perform some fancy error trapping. When you use -ErrorVariable, any errors that occur when running the cmdlet are written to the variable you specify as well as $error:

PS C:\> get-process foobar -errorvariable myerror
Get-Process : Cannot find a process with the name 'foobar'. Verify the process name and call the cmdlet again.
At line:1 char:12
+ get-process <<<< foobar -errorvariable myerror
PS C:\> $myerror
Get-Process : Cannot find a process with the name 'foobar'. Verify the process name and call the cmdlet again.
At line:1 char:12
+ get-process <<<< foobar -errorvariable myerror
PS C:\> $error[0]
Get-Process : Cannot find a process with the name 'foobar'. Verify the process name and call the cmdlet again.
At line:1 char:12
+ get-process <<<< foobar -errorvariable myerror
PS C:\>

In this example I attempted to get a non-existent process. I specified a variable for -ErrorVariable called myerror. As you can see, it is identical to the last error written to $error. But there is one big advantage. If I run another PowerShell command that generates an error, my Get-Process error moves down in order. After enough errors, it will be gone altogether.

However, if I need to refer back to the error I can still access it in $myerror. This variable is also an array like $error, although in this case it only has one entry which is why I can get by with simply invoking $myerror. To access any properties directly, I need to use an index number:

PS C:\> $myerror[0].categoryinfo

Category : ObjectNotFound
Activity : Get-Process
Reason : ProcessCommandException
TargetName : foobar
TargetType : String

Although it might be more thorough to treat $myerror as the array, it is in case the cmdlet raised more than one error:

PS C:\> $myerror | foreach {
>> write ("Exception: {0}" -f $_.Exception)
>> write ("Category: {0}" -f $_.CategoryInfo.Category)
>> write ("Command: {0}" -f $_.InvocationInfo.MyCommand)
>> }
>>
Exception: Microsoft.PowerShell.Commands.ProcessCommandException: Cannot find a process with the name 'foobar'. Verify
the process name and call the cmdlet again.
Category: ObjectNotFound
Command: Get-Process
PS C:\>

You can just as easily write this to a text file using Out-File, Set-Content or Add-Content. My mom always said we learn from our mistakes. Use -errorVariable to keep track of yours.