Error Handling Powershell Trap
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Error Handling In Powershell Script
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Powershell Error Handling Best Practices
Systems Management > PowerShell & Scripting > Scripting > Error Trapping and Handling in PowerShell Error Trapping and Handling in PowerShell How to use the Trap and Try...Catch...Finally constructs Jul 20, 2010 Don Jones | Windows IT Pro EMAIL Tweet Comments 0 Advertisement Sometimes when something goes wrong in Windows PowerShell, it isn't a bad thing. powershell error handling function That is, there are certain conditions that you can anticipate and potentially deal with, such as a missing file or a computer that can't be contacted over the network. In response, you might want to prompt the user for an action to take or just log the error so that you can try again later. Windows PowerShell makes this possible through a scheme called error trapping and handling. First, You Need an Error To trap and handle an error, you actually need one to occur. Technically, in PowerShell terminology, you need an exception to occur. That can actually be a little tricky to do, believe it or not. For example, try running the following command. It will fail, but pay attention to what happens: Get-WmiObject Win32_BIOS -comp 'localhost','not-here' First, you should see the Win32_BIOS instance from your local computer. Then, you should see an error message (unless you actually have a computer named not-here on your network). Think you've seen an exception? Wrong. In PowerShell
being able to handle errors helps to ensure that an unexpected event will not go on to wreck the system you are working
Powershell Error Handling Silentlycontinue
on. Take the example below. Every week in our sample company (MyCompany.Com) Human powershell error handling copy-item Resources are going to upload a list telling us who should have access to the Expenses database. If powershell error handling the rpc server is unavailable a name isn’t in the list from HR we’re going to remove it from the group and that user will no longer be able to log expense claims: $AuthorizedUsers= Get-Content \\ http://windowsitpro.com/scripting/error-trapping-and-handling-powershell FileServer\HRShare\UserList.txt $CurrentUsers=Get-ADGroupMember "Expenses Claimants" Foreach($User in $CurrentUsers) { If($AuthorizedUsers -notcontains $User) { Remove-ADGroupMember -Identity "Expenses Claimants" -User $User } } Now, you can see where this is going to go wrong. One week HR doesn’t get around to uploading the list or, just as we are about to access the list, the file server dies. Suddenly PowerShell throws an error on http://www.vexasoft.com/blogs/powershell/7255220-powershell-tutorial-try-catch-finally-and-error-handling-in-powershell the Get-Content cmdlet and the $AuthorizedUser variable remains empty. Because our script doesn’t handle errors, it continues to run and, in a very short space of time, it has removed every user from our expenses group. Pretty soon the irate phone calls start flooding in and life gets a little less happy. The way to avoid all this is to catch the errors and then handle the event that caused them (which in this case is halt the script and have a shout at someone in HR). Terminating and Non-Terminating Errors One of the key things to know when catching errors is that only certain errors can be caught by default. Errors come in two types – terminating and non-terminating. A terminating error is an error that will halt a function or operation. If you make a syntax error or run out of memory, that is a terminating error. Terminating errors can be caught and handled. Non-terminating errors allow Powershell to continue and usually come from cmdlets or other managed situations. Under normal circumstances they cannot be caught by Try-Catch-Finally. The Get-Content err
Trap statement includes a list of statements to run when a http://ss64.com/ps/trap.html terminating error occurs. By default, this will trap any http://powershell-tips.blogspot.com/2015/05/error-handling-with-trap.html terminating error or optionally you may specify an error type. A script or command can have multiple Trap statements. Trap statements can appear anywhere in the script or command. Examples A simple trap that error handling will traps any terminating error displays the error by using the $_ automatic variable: function TrapTest { trap {"Error found: $_"} thiswontwork } C:\PS> TrapTest Error found: The term 'thiswontwork' is not recognized as the name of a cmdlet, function, script file, or operable powershell error handling program. Check the spelling of the name, or if a path was included verify that the path is correct, and then try again. Use the Break and Continue keywords in a Trap statement to determine whether a script or command will continue to run after a terminating error. A Break statement within a Trap statement will stop the function or script: { trap {"Error trapped"; break;} A Continue statement within a Trap statement will resume execution after the statement that caused the error, just as it would without Break or Continue. { trap {"Error trapped"; continue;} "When elephant steps on a trap, no more trap" ~ African proverb Related: Try ... Catch - Handle a terminating error within a scriptblock about_Try_Catch_Finally © Copyright SS64.com 1999-2015 Some rights reserved
Try-Catch-Finally feature. We had trap construct for the same purpose. I think, Trap was a new concept as it was not there in any of the existing .NET-based languages. But Powershell v1.0 somehow had this unusual feature. In most of the old machines, there will be Powershell v1.0 and we cannot use Try-Catchblocksfor those servers. So if you are writing script for allversionsof Windows, there is no option left except usingTrap. Let us see theTrap example below: The above example will call two divide statement which will end up with divide-by-zero. There are two blocks where trap is declared : 1. At script level 2. At function level You will notice that output will call Function level when it will fail inside function block and it will callscript level trapwhen called outside function. Hope this simple example will make you learn this correctly. Please send me your questions and suggestion if you have any. Learning from small example is always better if you want to understand something correctly. That's it for today! Thanks for reading today and keep reading this blog which is updated everyday. Written by Som DT Email ThisBlogThis!Share to TwitterShare to FacebookShare to Pinterest Labels: General-Tips, Powershell Basics Your Rating : No comments: Post a Comment Newer Post Older Post Home Subscribe to: Post Comments (Atom) My Word Download my book on Powershell here.Send your comments in articles or write a mail to som.dt@gmx.com if you have any question or suggestion. Subscribe To Posts Atom Posts Comments Atom Comments Powershell-Tips Search Loading... Follow by Email Popular Posts #28 : Display Messagebox with Powershell Although, I never came accross such a situation where I need to throw a messagebox. But, just as I was playing, I tried to throw messagebox... #45 : Display top n lines or last n lines of a file Often we reach to a situation where we need to get top 10 or 100 lin