Отключить вывод ошибок powershell

You’re way off track here. Silencing errors is almost never a good idea, and manually checking $? explicitly after every single command is enormously cumbersome and easy to forget to do (error prone). Don’t set yourself up to easily make a mistake. If you’re getting lots and lots of red, that means your script kept going when it should have stopped instead. It can no longer do useful work if most of its commands are failing. Continuing a program when it and the system are in an unknown state will have unknown consequences; you could easily leave the system in a corrupt state.

The correct solution is to stop the algorithm on the first error. This principle is called «fail fast,» and PowerShell has a built in mechanism to enable that behavior. It is a setting called the error preference, and setting it to the highest level will make your script (and the child scopes if they don’t override it) behave this way:

$ErrorActionPreference = 'Stop'

This will produce a nice, big error message for your consumption and prevent the following commands from executing the first time something goes wrong, without having to check $? every single time you run a command. This makes the code vastly simpler and more reliable. I put it at the top of every single script I ever write, and you almost certainly should as well.

In the rare cases where you can be absolutely certain that allowing the script to continue makes sense, you can use one of two mechanisms:

• catch: This is the better and more flexible mechanism. You can wrap a try/catch block around multiple commands, allowing the first error to stop the sequence and jump into the handler where you can log it and then otherwise recover from it or rethrow it to bubble the error up even further. You can also limit the catch to specific errors, meaning that it will only be invoked in specific situations you anticipated rather than any error. (For example, failing to create a file because it already exists warrants a different response than a security failure.)
• The common -ErrorAction parameter: This parameter changes the error handling for one single function call, but you cannot limit it to specific types of errors. You should only use this if you can be certain that the script can continue on any error, not just the ones you can anticipate.

In your case, you probably want one big try/catch block around your entire program. Then your process will stop on the first error and the catch block can log it before exiting. This will remove a lot of duplicate code from your program in addition to cleaning up your log file and terminal output and making your program less likely to cause problems.

Do note that this doesn’t handle the case when external executables fail (exit code nonzero, conventionally), so you do still need to check $LASTEXITCODE if you invoke any. Despite this limitation, the setting still saves a lot of code and effort.

Additional reliability

You might also want to consider using strict mode:

Set-StrictMode -Version Latest

This prevents PowerShell from silently proceeding when you use a non-existent variable and in other weird situations. (See the -Version parameter for details about what it restricts.)

Combining these two settings makes PowerShell much more of fail-fast language, which makes programming in it vastly easier.

How do you make powershell ignore failures on legacy commands?

All powershell modules support -ErrorAction, however that does not work with legacy commands like NET STOP

NET STOP WUAUSERV
echo $?
true

I want to attempt to stop the service, and if the service is already stopped, continue. An easy way to reproduce this is to try and stop the service twice.

Things I’ve tried

$ErrorActionPreference = "SilentlyContinue"
NET STOP WUAUSERV
NET STOP WUAUSERV
echo $LASTEXITCODE

Tried using AND and OR operrators

and

NET STOP WUAUSERV || $true
NET STOP WUAUSERV || $true
echo $LASTEXITCODE

or

NET STOP WUAUSERV && $true
NET STOP WUAUSERV && $true
echo $LASTEXITCODE

I’ve also tried redirecting errors

NET STOP WUAUSERV 2>nul
NET STOP WUAUSERV 2>nul
echo $LASTEXITCODE

As recommended in a similar question, I’ve also tried

cmd.exe /C "NET STOP WUAUSERV"

How can I make this legacy command idempotent?

1. Introduction to Error Action in PowerShell
2. Use the -ErrorAction Parameter in PowerShell
3. Setting Error Action Preferences in PowerShell

Whether we want to ignore error messages or terminate a script’s execution when an error occurs, Windows PowerShell has plenty of options for dealing with errors. This article will discuss multiple techniques in handling and suppressing errors.

Introduction to Error Action in PowerShell

Even though it is effortless to suppress Windows PowerShell errors, doing so isn’t always the best option (although it can be). If we carelessly tell PowerShell to hide errors, it can cause our script to behave unpredictably.

Suppressing error messages also makes troubleshooting and information gathering a lot more complicated. So tread lightly and be careful about using the following snippets that you will see in this article.

Use the -ErrorAction Parameter in PowerShell

The most common method for dealing with errors is to append the -ErrorAction parameter switch to a cmdlet. The -ErrorAction parameter switch lets PowerShell tell what to do if the cmdlet produces an error.

Command:

Get-Service 'svc_not_existing' -ErrorAction SilentlyContinue

In the command above, we are querying for a service that doesn’t exist. Usually, PowerShell will throw an error if the service doesn’t exist.

Since we use the -ErrorAction parameter, the script will continue as expected, like it doesn’t have an error.

Setting Error Action Preferences in PowerShell

If we need a script to behave in a certain way (such as suppressing errors), we might consider setting up some preference variables. Preference variables act as configuration settings for PowerShell.

We might use a preference variable to control the number of history items that PowerShell retains or force PowerShell to ask the user before performing specific actions.

For example, here is how you can use a preference variable to set the -ErrorAction parameter to SilentlyContinue for the entire session.

Command:

$ErrorActionPreference = 'SilentlyContinue'

There are many other error actions that we can specify for the ErrorAction switch parameter.

• Continue: PowerShell will display the error message, but the script will continue to run.
• Ignore: PowerShell does not produce any error message, writes any error output on the host, and continues execution.
• Stop: PowerShell will display the error message and stop running the script.
• Inquire: PowerShell displays the error message but will ask for confirmation first if the user wants to continue.
• SilentlyContinue: PowerShell silently continues with code execution if the code does not work or has non-terminating errors.
• Suspend: PowerShell suspends the workflow of the script.

As previously mentioned, the -ErrorAction switch has to be used in conjunction with a PowerShell cmdlet. For instance, we used the Get-Process cmdlet to demonstrate how the ErrorAction switch works.

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