How to save powershell hyper-v errors to file

Question

I am making a script to turn virtual machines on and off in hyper-v. Sometimes the Stop-VM command fails and I need to save the bug or reflect it in some way in a log file

I tried putting the command in a trycath but it didn't work.

Command:

Stop-VM $VMapagar

Sometimes the command gives me this error and does not turn off the machine

Stop-VM: Could not stop.

I would like to be able to reflect the failure in some way in a log.txt Thanks!

Scepticalist · Answer 1 · 2021-06-25T14:17:59.680

Use Try..Catch to trap the error by telling PS to treat it as a terminating error, then process it as you require:

# Rest of your script
Try {
    # Run your command, but tell PS to stop if it find an error
    # You can explore the effects of the other possible values for -ErrorAction in PS documentation.
    Stop-VM $VMpagar -ErrorAction Stop
    # If it's got this far, then there can't have been an error so write a success message to console
    Write-Host "OK"
}
Catch {
    # This code will process if there was an error in the "Try" block
    # By default, within the "Catch" block, the "$_" variable contains the error message
    Write-Host "Error: $_"
    # Write the error to a log file - "`n" tells PS to write a newline before the subsequent text
    Add-Content -Path 'c:\temp\log.txt' -Value "`n$_"
    # You could stop the script here using "Throw" or "Exit" commands if you want the whole script to stop on ANY error
}
# Your script will continue from this point if you haven't stopped it

mklement0 · Accepted Answer · 2021-06-26T13:10:40.090

Scepticalist's helpful answer shows how to capture a terminating error, by using the common -ErrorAction (-ea) parameter with value 'Stop' in order to promote non-terminating errors (the most common kind) to terminating ones, which allows them to be trapped with a try/ catch / finally statement.
- Note that this approach limits you to capturing the first non-terminating error (whereas a single cmdlet call may emit multiple ones), because it - thanks to -ErrorAction Stop - then instantly terminates the statement and transfers control the catch block (where the automatic $_ variable reflects the triggering error in the form of an [ErrorRecord] instance).
- Also note that execution continues after a catch block by default - unless you explicitly use throw to re-throw the terminating error (or use a statement such as exit to exit the script).
To capture - potentially multiple - non-terminating errors you have two options:
- Redirect them directly to a file, using the redirection operator > with the number of the error stream, 2:
  - Stop-Vm $vms 2>errs.txt
  - This sends any errors quietly to file errs.txt; that is, you won't see them in the console. If no errors occur, an empty file is created.
  - Note: This technique is the only option for directly redirecting an external program's errors (stderr output); however, using redirection 2>&1 you can capture success output (stdout) and errors (stderr) combined, and split them by their source stream later - see the bottom section of this answer.
- Use the common -ErrorVariable (-ev) parameter to collect any non-terminating errors in a variable - note that the target variable must be specified without the $:
  - Stop-Vm $vms -ErrorVariable errs
  - By default, the errors are still output as well and therefore print to the console (host) by default, but you can add -ErrorAction SilentlyContinue to prevent that. Caveat: Do not use -ErrorAction Ignore, as that will categorically suppress errors and prevent their collection.
  - You can then inspect the $errs array (list), which is empty if no errors occurred and otherwise contains one or more [ErrorRecord] instances, and send the collected errors to a file on demand; e.g.:
    - if ($errs) { $errs > errs.txt }

How to save powershell hyper-v errors to file

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