dwdii - Daniel Dittenhafer

How to Get Error Exception Details in PowerShell Catch Block

For the last couple of weeks I have been required to import a data log file (CSV) from a legacy SCADA system into my centralized data management system. It occured to me today that I might be able to use PowerShell to automate some of the importing steps which include import to a DEV, QA and Production system. I’m still working on this script, but in the process of developing it, I had a need to learn more about an exception that was occuring in the script. I had my try catch block already specified, but was simply using Write-Error, as in the following code sample, to report a generic message “Failed to…” whenever the catch block was executed.

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try 
{ 
	$session = Logon... 
} 
catch 
{ 
	Write-Error "Failed to logon to DMS." 
}

I searched the local PowerShell help and didn’t see any info on how to get more detail about a given exception. I searched a little online including about_Try_Catch_Finally and didn’t find any gems. Then I thought “Maybe there is a global object, like $host, that as some error info”. I tried $Err and $Error with no success… then I tried $_ and surprise! It resulted in an object with exception details! See the code sample below, where the $_ object is used in the catch block and converted to a string for output to the Write-Error stream.

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try
{
    $session = Logon...
}
catch
{
    # Using $_ in the catch block to include more details about the error that occured.
    Write-Error ("Failed to logon to DMS." + $_)
}

When I run through Get-Member, the $_ object in the catch block returns the following result:

TypeName: System.Management.Automation.ErrorRecord
Name MemberType Definition
Equals Method bool Equals(System.Object obj)
GetHashCode Method int GetHashCode()
GetObjectData Method System.Void GetObjectData(System.Runtime.Serialization.SerializationInfo info, System.Runtime.Serialization.StreamingContext context)
GetType Method type GetType()
ToString Method string ToString()
CategoryInfo Property System.Management.Automation.ErrorCategoryInfo CategoryInfo {get;}
ErrorDetails Property System.Management.Automation.ErrorDetails ErrorDetails {get;set;}
Exception Property System.Exception Exception {get;}
FullyQualifiedErrorId Property System.String FullyQualifiedErrorId {get;}
InvocationInfo Property System.Management.Automation.InvocationInfo InvocationInfo {get;}
PipelineIterationInfo Property System.Collections.ObjectModel.ReadOnlyCollection'1[[System.Int32, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]] PipelineIterationInfo {get;}
TargetObject Property System.Object TargetObject {get;}
PSMessageDetails ScriptProperty System.Object PSMessageDetails {get=& { Set-StrictMode -Version 1; $this.Exception.InnerException.PSMessageDetails };}

Of course, after having figured this out, I thought “Hmm… I bet others might have the same question about getting more exception detail inside a catch block”, and so was born this blog entry. Hope it helps!

Thanks for reading!

Daniel (@dwdii)

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