Problems writing to file inside cmdlet? - powershell

Question

I only dabble in PS so I'm probably missing something obvious, but this seems like it should work lol
I've got a filewatcher, looks for a specific file in a specific folder, when found it triggers an action. The action first writes to screen, then to logfile then triggers a follow-up script.
Writing to screen works, writing to logfile doesn't, triggering follow up script works too. I actually tried the writing to logfile a few different ways, even building a function before this part and calling it, like a Write-Log instead of Write-Host but it doesn't work either.
Is there a special means to write to log in the manner I'm trying?
$folder = 'D:\InputFiles\'
$filter = 'data.csv'
$LogFile = "D:\APIRead\logs\master.log"
$fsw = New-Object IO.FileSystemWatcher $folder, $filter -Property #{IncludeSubdirectories = $false;NotifyFilter = [IO.NotifyFilters]'FileName, LastWrite'}
Register-ObjectEvent $fsw Created -SourceIdentifier PaymentsMKFileCreated -Action {
$name = $Event.SourceEventArgs.Name
$changeType = $Event.SourceEventArgs.ChangeType
$timeStamp = $Event.TimeGenerated
$Output = "The file '$name' was $changeType at $timeStamp"
Write-Host $Output
Out-File -FilePath $LogFile -InputObject $Output -Append
#Invoke-Item 'D:\APIRead\scripts\process.bat'
}

Answer 1

$LogFile = "D:\APIRead\logs\master.log"
Try moving this line inside of your Event -Action
It could be trying to expand $LogFile, but it is not defined in the Action's scope.

Answer 2

Grok42's helpful answer offers a pragmatic solution to the problem: defining $LogFile inside the -Action script block by definition makes it available there (but only there).
Indeed, a script block { ... } passed to the -Action parameter of the Register-ObjectEvent cmdlet does not generally see variables defined in the caller's scope (unless those variables happen to be defined in the global scope), because such a script block runs in a dynamic module.
However, you may still want to declare your $LogFile variable in the caller's scope while also allowing it to be referenced in the -Action script block, so that both scopes can act on it.
To that end, you can use Register-ObjectEvent's -MessageData parameter to pass a value to the -Action script block, which it can reference as $Event.MessageData, via the automatic $Event variable:
$folder = 'D:\InputFiles\'
$filter = 'data.csv'
$LogFile = "D:\APIRead\logs\master.log"
$fsw = New-Object IO.FileSystemWatcher $folder, $filter -Property #{IncludeSubdirectories = $false; NotifyFilter = [IO.NotifyFilters]'FileName, LastWrite' }
# Note the use of -MessageData
Register-ObjectEvent $fsw Created -SourceIdentifier PaymentsMKFileCreated -MessageData $LogFile -Action {
$name = $Event.SourceEventArgs.Name
$changeType = $Event.SourceEventArgs.ChangeType
$timeStamp = $Event.TimeGenerated
$logFile = $Event.MessageData # Get the log file path from the -MessageData argument
$Output = "The file '$name' was $changeType at $timeStamp"
Write-Host $Output
Out-File -FilePath $logFile -InputObject $Output -Append
}
Note:
For an example of passing multiple values from the caller's scope to the -Action script block, using a hashtable, see this answer.
It's even possible to pass the caller's entire state to -MessageData, via $ExecutionContext.SessionState, which allows the -Action block to retrieve any variable from the caller's state via $Event.MessageData.PSVariable.GetValue('varName')

Answer 3

removed the ** after append and make sure you have permissions to the directory you are writing to.
Adding -Force makes it create the file if it doesn't exist.
Out-File -FilePath $LogFile -InputObject $Output -Append -Force