Error Handling In Powershell Example
Contents |
being able to handle errors helps to ensure that an unexpected event will not go on to wreck the system you are powershell error handling try catch working on. Take the example below. Every week in our sample company powershell erroraction stop try catch (MyCompany.Com) Human Resources are going to upload a list telling us who should have access to the Expenses powershell try catch database. If 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
Powershell Try Catch Syntax
claims: $AuthorizedUsers= Get-Content \\ 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 error handling in powershell script PowerShell throws an error on 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 norm
Steps (4 total) 1 Writing a Try Catch block The try catch block is written below. Place the code you want to execute in the try section. This will be ran first, powershell error handling best practices then you can use the catch blow to get errors and take actions on
Powershell Error Handling Function
those errors. Try { #Do some stuff } Catch { #Got an error do something else } 2 Simple Get-ADuser Try
Powershell Error Handling Silentlycontinue
Catch example $Users = Get-Content C:\temp\usersimport.txt foreach ($User in $Users) { try { Get-ADUser -Identity $User | Out-Null Write-Output "$user exists" } catch { write-output "$User doesn't exist" } } 3 Getting error exceptions http://www.vexasoft.com/blogs/powershell/7255220-powershell-tutorial-try-catch-finally-and-error-handling-in-powershell for catching specific errors. First you must generate the error you want to catch. For example query a user you know doesn't exists and then execute this line of code. $Error[0] | fl * -Force PowerShell stores all error data in $Error so we can get the contents of it. Gain we are after the exception code, which is highlighted in yellow. $Error[0] | fl * -Force 4 Add https://community.spiceworks.com/how_to/121063-using-try-catch-powershell-error-handling exceptions to catch statements We will now add a catch with the exception to catch only that error and do something special. $Users = Get-Content C:\temp\usersimport.txt foreach ($User in $Users) { try { Get-ADUser -Identity $User | Out-Null Write-Output "$user exists" } catch [Microsoft.ActiveDirectory.Management.ADIdentityNotFoundException]{ Write-Host "$User doesn't exist" -ForegroundColor Red } catch { Write-Output "Something else bad happend" } } Conclusion Use this instead of several if else statements and catch specific errors to aid in error handling. References Hey, Scripting Guy! Blog 8 Comments Mace Bryce Katz Jul 13, 2015 at 01:56pm Nicely done! I've wondered about the specific syntax of TRY ... CATCH for a while. Chipotle NetTechMike Jul 13, 2015 at 06:43pm This is fantastic. I wish Microsoft used this method of error handling when they create scripts in System Center. Serrano Tyler9771 Jul 13, 2015 at 07:04pm This is neat, I will have to try it out the next time I attempt some PowerShell Scriptin' Cayenne MerlinYoda Jul 13, 2015 at 09:30pm Nice write-up. Short and sweet. I haven't looked into PowerShell much (I know, I know. I should), but I'm glad to see they've got the the old Try-Catch statement (first saw one of those back in the day when learnin
| Related Tips: More > PowerShell Problem PowerShell V2 introduces the "try-catch-finally" statements, similar to those you already use when you write .NET code. "Try-catch-finally" encloses a block https://www.mssqltips.com/sqlservertip/3509/error-handling-with-trycatchfinally-in-powershell-for-sql-server/ of script that is likely to produce errors under specific circumstances and therefore helps you to keep your code organized. Below you'll find a short usage guide for this error handling construct. http://wragg.io/powershell-try-catch/ This was done using Windows 8.1 Pro x64 / PowerShell v4 / SQL Server 2012 SP1 environment. Solution Open a new PowerShell session and make sure that the SQLPS module is error handling not imported. If you run Get-Module, SQLPS should not be in the result list. For example, if you use the Windows PowerShell ISE: Get-Module Compare this result with the one you obtain after importing SQLPS: Import-Module SQLPS -DisableNameChecking Get-Module Now when we run this piece of code - remember that SQLPS is not loaded. Set-Location SQLSERVER:\SQL\MyServer\DEFAULT\DATABASES Write-Host -ForegroundColor Green "Done" The result should look powershell error handling like: Since SQLPS is not loaded, PowerShell returns a "drive not found" exception. Notice that this error is a non-terminating error and the "Done" message will be part of the result. You won't be able to reproduce this situation when running PowerShell from within SQL Server Management Studio, because the SQL Server specific cmdlets and provider are already loaded on start. Right click, for example, on the Server node in the object view pane, click on "Start PowerShell" and run Get-Module. Now let's enclose the above error prone line of code in a "try-catch" as follows: try{ Set-Location SQLSERVER:\SQL\MyServer\DEFAULT\DATABASES Write-Host -ForegroundColor Green "Done" } catch{ Write-Host -ForegroundColor DarkYellow "You're WRONG" Write-Host -ForegroundColor Magenta $Error[0].Exception } finally{ Write-Host -ForegroundColor Cyan "It's finally over..." } As you can see, the result is similar to what you've obtained before, except the last line which comes from the "finally" line of code. The "catch" code is not executed. For a non-terminating error, adding a "try-catch" construct has no effect unless you add an "error action" parameter or preference set to "stop", forcing it to become a terminating error as shown below: try{ Set-Location SQLSERVER:\SQ
script to be unable to remotely connect to some of my servers. Initially I handled the result of these exceptions with If..Else blocks, but it felt like a Try..Catch might be more appropriate. -- Spoiler alert: On this occasion it actually turned out it wasn't, but it's a useful technique regardless. While Master Yoda does not believe in a "Try", Powershell fortunately does. But there are some caveats to using this technique which I will detail below. In case you're not aware performing a Try..Catch is as simple as: Try{ Do-something }Catch{ Do-something else, but only if a terminating error has occurred. } Additionally you can extend this to include: }finally{ Do-something always, whether a terminating error occurred or not. } A Finally block can be useful as it will always execute when an error does not occur, but it will also execute if CTRL+C or an Exit keyword is used to stop the script from within a Catch block. Here are some other useful things to know about Try..Catch: #1: The Catch block will only execute if a terminating error has occurred Powershell errors come in two forms, terminating and non-terminating: An error is a terminating error if: it prevents your cmdlet from continuing to process the current object or from successfully processing any further input objects, regardless of their content. you do not want your cmdlet to continue processing the current object or any further input objects, regardless of their content. it occurs in a cmdlet that does not accept or return an object or if it occurs in a cmdlet that accepts or returns only one object. An error is a non-terminating error if: you want your cmdlet to continue processing the current object and any further input objects. it is related to a specific input object or subset of input objects. Source: https://msdn.microsoft.com/en-us/library/ms714414(v=vs.85).aspx If your catch block is not executing, your error is either non-terminating or not throwing an error at all. But.. #2: You can force a cmdlet to throw a terminating error by using the -erroraction parameter The -erroraction parameter is available for any cmdlet that supports common parameters. There are the following options for this parameter: 0 : SilentlyContinue. This suppresses