Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people, just like you, are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
Solved

Powershell Exeception Question

Posted on 2012-03-20
7
366 Views
Last Modified: 2012-03-22
Hi,

I am trying to understand why a simple try / catch block is not capturing exceptions.

From the code below I expect it the output to be:

Start..
Test1..
Exception 1...
Test2..
Exception 2...

However instead I get:

PS C:\> .\exception_test.ps1
Attempted to divide by zero.
At C:\exception_test.ps1:6 char:10
+     $a = 1 / <<<<  0
    + CategoryInfo          : NotSpecified: (:) [], RuntimeException
    + FullyQualifiedErrorId : RuntimeException

PS C:\>

So what am I doing wrong ?

The code is below.

Thanks,

Ward.

PS testPC is a non-existant pc.

write-Host "Start.."

try 
{ 
	Write-Host "Test1.."
	$a = 1 / 0 
}

catch 
{	
	write-host "Exception 1..." 
}

try 
{ 	
	Write-Host "Test2.."
	$wmi_objects = Get-WmiObject "Win32_Process" -computer "testPC" 
}

catch 
{	
	write-host "Exception 2..." 
}

Open in new window

0
Comment
Question by:whorsfall
  • 3
  • 3
7 Comments
 
LVL 16

Expert Comment

by:Dale Harris
ID: 37745465
You can't divide by 0.  

$a = 1 / 0

What exactly are you trying to do?
0
 
LVL 16

Expert Comment

by:Dale Harris
ID: 37745471
Are those supposed to be placeholders for computers you're trying to ping?  If that's the case, it would look something like this:

$Count = $Computers.count

$a = "1/$count"

Does that make sense?
0
 
LVL 8

Expert Comment

by:Brent Challis
ID: 37745535
Your problem with the sample code seems to be that the PowerShell environment is detecting that you have written a divide by zero.  If he code s modified so that it has to run before the problem is detected to try/catch works as you would expect.  e.g.
 Set-StrictMode -Version "Latest"
write-Host "Start.."
$den = 0
try
{
      Write-Host "Test1.."
      $a = 1 / $den
}
catch
{      
      write-host "Exception 1..."
}

try
{       
      Write-Host "Test2.."
      $wmi_objects = Get-WmiObject "Win32_Process" -computer "testPC"
}
catch
{      
      write-host "Exception 2..."
}

produces

Start..
Test1..
Exception 1...
Test2..
Exception 2...
0
Is Your AD Toolbox Looking More Like a Toybox?

Managing Active Directory can get complicated.  Often, the native tools for managing AD are just not up to the task.  The largest Active Directory installations in the world have relied on one tool to manage their day-to-day administration tasks: Hyena. Start your trial today.

 

Author Comment

by:whorsfall
ID: 37745606
Hi,

Hmm. Can u elaborate a bit futther - provide a more detailed explination.

I looked at the Set-StrictMode and still am confused why my orignal code would of not worked.

I am missing the point here :)

Thanks,

Ward
0
 
LVL 16

Expert Comment

by:Dale Harris
ID: 37745650
I think the core of the issue is that you are trying to do an illegal operation to make an error.  The problem is, the try/catch/finally is geared towards legitimate returns of errors.  For example, if you try to ping a null value, I don't think the try/catch would work, but if you try to ping and get an error that the computer could not be reached, it would be thrown to the catch portion.

Does that make sense?
0
 
LVL 8

Accepted Solution

by:
Brent Challis earned 500 total points
ID: 37745662
The Set-StrictMode is simply my standard starting point and is not actually relevant here.  

What seems to be happening is that when you ask PowerShell to run the script it parses it.  In that process is sees that there is a divide by zero issue as you have hard coded the 0 as the denominator, so it errors out.  This can be seen by the fact that the error message turns up before any of the Write-Host cmdlet output that should have occurred before it gets to the error line.  By changing the denominator to a variable the parsing can't determine that there is an error so the code is executed. We get the Write-Host output, then we get a run time error as the division is performed using a variable that has the value of 0 which is processed in the catch block and then we continue through the code..
0
 
LVL 8

Expert Comment

by:Brent Challis
ID: 37745666
You may also need to set the ErrorActionPreference to enable PowerShell to move past the error as well so that the catch block can process the exception:
$ErrorActionPreference = "Stop"
0

Featured Post

Announcing the Most Valuable Experts of 2016

MVEs are more concerned with the satisfaction of those they help than with the considerable points they can earn. They are the types of people you feel privileged to call colleagues. Join us in honoring this amazing group of Experts.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Utilizing an array to gracefully append to a list of EmailAddresses
In this previous article (https://oddytee.wordpress.com/2016/05/05/provision-new-office-365-user-and-mailbox-from-exchange-hybrid-via-powershell/), we made basic license assignments to users in O365. When I say basic, the method is the simplest way …
Learn the basics of if, else, and elif statements in Python 2.7. Use "if" statements to test a specified condition.: The structure of an if statement is as follows: (CODE) Use "else" statements to allow the execution of an alternative, if the …
Learn how to match and substitute tagged data using PHP regular expressions. Demonstrated on Windows 7, but also applies to other operating systems. Demonstrated technique applies to PHP (all versions) and Firefox, but very similar techniques will w…

860 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question