Register-ObjectEvent cmdlet not working properly on Powershell but working on ISE

Gregor y provided the crucial hint in a comment:

To ensure that your script keeps processing events indefinitely, you can use a Wait-Event call at the end of your script to indefinitely wait for events that will never arrive, which keeps your script running, but - unlike Start-Sleep - does not block processing of events via the script block passed to Register-ObjectEvent's -Action parameter:

$Watcher = New-Object System.IO.FileSystemWatcher
$Watcher.path = "\\192.168.5.127\data\TestWatcher"
$Destination = "C:\TestWatcher"
$Watcher.EnableRaisingEvents = $true

$action = {
    $path = $event.SourceEventArgs.FullPath
    $name = $event.SourceEventArgs.Name
    $changetype = $event.SourceEventArgs.ChangeType
    Write-Host "File $name at path $path was $changetype at $(get-date)"
    Copy-Item $Watcher.path $Destination
}

# Register the event with a self-chosen name passed to -SourceIdentifier
# and an -Action script block.
$eventJob = 
  Register-ObjectEvent $Watcher Created -SourceIdentifier FileWatcher -Action $action

# Now wait indefinitely for an event with the same source identifier to arrive.
# NONE will ever arrive, because the events are handled via the -Action script block.
# However, the call will prevent your script from exiting, without
# blocking the processing of events in the -Action script block.
# Use Ctrl-C to exit the script; the `finally` clause ensures cleanup.
try {
  Wait-Event -SourceIdentifier FileWatcher
} 
finally {
  # Clean up: Remove the event job, which also unregisters the event.
  $eventJob | Remove-Job -Force 
}

Alternatively, make do without an -Action script block and process events in a Wait-Event loop:

$Watcher = New-Object System.IO.FileSystemWatcher
$Watcher.path = "\\192.168.5.127\data\TestWatcher"
$Destination = "C:\TestWatcher"
$Watcher.EnableRaisingEvents = $true

# Register the event with a self-chosen name passed to -SourceIdentifier
# but WITHOUT an -Action script block.
Register-ObjectEvent $Watcher 'Created' -SourceIdentifier FileWatcher

# Now use Wait-Event with the chosen source identifier to
# to indefinitely receive and then process the events as they 
# become available.
try {
  while ($event = Wait-Event -SourceIdentifier FileWatcher) {
    $path = $event.SourceEventArgs.FullPath
    $name = $event.SourceEventArgs.Name
    $changetype = $event.SourceEventArgs.ChangeType
    Write-Host "File $name at path $path was $changetype at $(Get-Date)"
    Copy-Item $Watcher.path $Destination
    $event | Remove-Event # Note: Events must be manually removed.
  }
}
finally {
  # Clean up.
  Unregister-Event -SourceIdentifier FileWatcher
}

Alternative with event-polling loop that permits foreground activity:

You can adapt the above to use a polling approach, by using an unconditional infinite loop, and replacing Wait-Event with a Get-Event call inside the loop body, followed by short sleep intervals (via Start-Sleep), which allows you to perform foreground activities while no events are being received:

$Watcher = New-Object System.IO.FileSystemWatcher
$Watcher.path = "\\192.168.5.127\data\TestWatcher"
$Destination = "C:\TestWatcher"
$Watcher.EnableRaisingEvents = $true

# Register the event with a self-chosen name passed to -SourceIdentifier
# but WITHOUT an -Action script block.
Register-ObjectEvent $Watcher 'Created' -SourceIdentifier FileWatcher

# Now enter an infinite loop that uses Get-Event to poll for
# available events and processes them.
# If none are available, foreground activity can be performed
# (which should be short-lived, otherwise event retrieval is blocked).
try {
  while ($true) {
    if ($event = Get-Event | Where-Object SourceIdentifier -eq FileWatcher) {
      $path = $event.SourceEventArgs.FullPath
      $name = $event.SourceEventArgs.Name
      $changetype = $event.SourceEventArgs.ChangeType
      Write-Host "File $name at path $path was $changetype at $(Get-Date)"
      Copy-Item $Watcher.path $Destination
      $event | Remove-Event # Note: Events must be manually removed.
    } else { # No event available.
      # Perform (short-lived) foreground activities here.
      Write-Host -NoNewline .
      Start-Sleep -Milliseconds 500 # Sleep a little, to avoid a tight loop.
    }
  }
}
finally {
  # Clean up.
  Unregister-Event -SourceIdentifier FileWatcher
}

Note:

• Due to a bug present up to at least PowerShell v7.3.x, Get-Event doesn't work with the -SourceIdentifier parameter, hence the Get-Event | Where-Object SourceIdentifier -eq FileWatcher workaround above.
  • See GitHub issue #11705.