Microsoft PowerShell and Nested Try/Catch

April 15, 2016

PowerShell

On a recent project, I learned something new about PowerShell’s Try/Catch. You can nest another Try/Catch in the Catch of the first Try/Catch. When I showed this to my PowerShell mentor, he said he didn’t know that could be done. I figured I might as well make a quick post about it.

I was using some code from Jeremy Saunders to gather CPU information on a XenApp 6.5 farm. the Get-XAServer cmdlet has a property to store the FQDN of a XenApp server but it is not populated. This XenApp farm contained servers in two different forests and two different domains. All my scripts I wrote for the project using the XenApp cmdlets and Get-EventLog stuff worked with no issues. Using Get-WmiObject broke because that cmdlet will not work for computers not in the same forest.

I did a Get-Help Get-WmiObject and noticed a -Authority parameter.

Get-WmiObject [-Authority <string>] [-Amended] [-AsJob] [-Authentication {Default | None | Connect | Call | Packet
| PacketIntegrity | PacketPrivacy | Unchanged}] [-ComputerName <string[]>] [-Credential <PSCredential>] [-EnableAll
Privileges] [-Impersonation {Default | Anonymous | Identify | Impersonate | Delegate}] [-Locale <string>] [-Namespa
ce <string>] [-ThrottleLimit <int>] [<CommonParameters>]

The explanation for that parameter:

-Authority <string>
Specifies the authority to use to authenticate the WMI connection. You can specify standard NTLM or Kerberos au
thentication. To use NTLM, set the authority setting to ntlmdomain:<DomainName>, where <DomainName> identifies
a valid NTLM domain name. To use Kerberos, specify kerberos:<DomainName>\<ServerName>". You cannot include the
authority setting when you connect to the local computer.

I wondered if I could use -Authority ntlmdomain:<DomainName> if the first Get-WmiObject failed.

Jeremy’s code wraps the call to Get-WmiObject in a Try {} Catch {}. So I thought it would be worth testing to see if I could do:

try
{
}

catch
{
	try
	{
	}
	
	catch
	{
	}
}

Sure enough it worked (and surprised me).

Here are the basics of Jeremy’s code.

add-pssnapin "citrix.xenapp.commands"

$names = Get-XAServer -ea 0 | Select ServerName | Sort ServerName 

foreach($name in $names)
{
	write-host "$($name.servername)"
	Try 
	{
		$ComputerInformation = Get-WmiObject -Class Win32_ComputerSystem -computername $Name.servername -ErrorAction Stop
		$Processors = Get-WmiObject -Class win32_Processor -computername $Name.servername -ErrorAction Stop 
		$Disks = Get-WmiObject -Class win32_LogicalDisk -computername $Name.servername -ErrorAction Stop
	}

	Catch 
	{
		Try 
		{
			$ComputerInformation = Get-WmiObject -Authority ntlmdomain:domain2 -Class Win32_ComputerSystem -computername $Name.servername -ErrorAction Stop
			$Processors = Get-WmiObject -Authority ntlmdomain:domain2 -Class win32_Processor -computername $Name.servername -ErrorAction Stop
			$Disks = Get-WmiObject -Authority ntlmdomain:domain2 -Class win32_LogicalDisk -computername $Name.servername -ErrorAction Stop
		}

		Catch
		{
			$ErrorDescription = "Error connecting using the Get-WmiObject cmdlet."
			$Host.UI.WriteErrorLine("*ERROR*: - $ErrorDescription")
		}
	}
}

None of this would have been necessary if Citrix had populated the ServerFqdn property. If they had, I could have just stripped the domain part off and just used one call to Get-WmiObject.

Hey, learn something new every day in this field.

Thanks

Webster

About Carl Webster

Webster is a Sr. Solutions Architect for Choice Solutions, LLC and specializes in Citrix, Active Directory and Technical Documentation. Webster has been working with Citrix products for many years starting with Multi-User OS/2 in 1990.

View all posts by Carl Webster

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