电源外壳。无法从 {} 获取变量

Question

在下面的代码中，有一个名为“$action”= {...} 的参数。括号内有一些变量($path、$logPath 等)。如何从大括号“{}”之外的参数访问变量？我需要我的一个函数(“RunFunctions”)的结果一段时间循环。或者，如果这是一个愚蠢的问题，请您指出我可以找到有关此 {} 表示法的一些信息的地方吗？谢谢。

try {
    ### SET FOLDER TO WATCH + FILES TO WATCH + SUBFOLDERS YES/NO
    $watcher = New-Object System.IO.FileSystemWatcher
    $watcher.Path = "C:\Testers\ResetOptimisation\tracking"
    $watcher.Filter = "user_name*.*"
    $watcher.IncludeSubdirectories = $true
    $watcher.EnableRaisingEvents = $true

    ### DEFINE ACTIONS AFTER AN EVENT IS DETECTED
    $action = { $path = $Event.SourceEventArgs.FullPath
                $logPath = "C:\Testers\ResetOptimisation\output\log.txt"
                $changeType = $Event.SourceEventArgs.ChangeType
                $logline = "$(Get-Date), $changeType, $path"
                Add-content $logPath -value $logline
                $terminateFlag = RunFunctions $path $changeType $logPath
            }

    ### DECIDE WHICH EVENTS SHOULD BE WATCHED
    Register-ObjectEvent $watcher "Created" -Action $action
    Register-ObjectEvent $watcher "Changed" -Action $action
    Register-ObjectEvent $watcher "Deleted" -Action $action
    Register-ObjectEvent $watcher "Renamed" -Action $action
    while ($true) {
        Write-Host $teminateFlag
        if ($teminateFlag -eq 1) {
            Exit
        }
        Start-Sleep 3
    }
}
catch {
    Write-Host $_
}

Answer 1

{ ... } 是一个脚本 block (字面意思) - 一段可重用的 PowerShell 代码，您可以按需执行(如函数指针或委托(delegate))其他语言)。

通过将存储在变量 $action 中的这样的 block 传递给 Register-ObjectEvent -Action，只要感兴趣的事件触发，PowerShell 就会调用它，并在一个动态模块，其范围与调用者的范围完全分开。

因此，您的调用代码看不到 block 内创建的变量，因为它们是该 block 的本地变量。

^{有关 PowerShell 中作用域的更多信息，请参阅 this answer 的底部部分.}

虽然 PowerShell通常也允许您在其他范围内创建和修改变量，但如果您采取明确的操作，这不是一个选项使用Register-ObjectEvent -Action，因为动态模块的作用域从根本上来说无法访问调用者的作用域，只能访问全局作用域。

# !! This works, but is ill-advised.
$global:terminateFlag = RunFunctions $path $changeType $logPath

但是，最好避免使用全局作用域，因为全局变量甚至在脚本退出后仍然存在(它们是 session -全局的)。

更好的解决方案是:

• 使操作脚本 block 输出调用者的值。

• 让调用者使用事件作业通过 Receive-Job 接收输出
  Register-ObjectEvent -Action 返回。

这是一个演示该技术的简化的独立示例:

它设置一个观察程序，附加一个事件处理程序，并创建一个触发观察程序事件的文件。

try {

  # Specify the target folder: the system's temp folder in this example.
  $dir = (Get-Item -EA Ignore temp:).FullName; if (-not $dir) { $dir = $env:TEMP }

  # Create and initialize the watcher.
  $watcher = [System.IO.FileSystemWatcher] @{
    Filter                = '*.tmp'
    Path                  = $dir
  }

  # Define the action script block (event handler).
  $action = {
    # Print the event data to the host.
    Write-Host "Event raised:`n$($EventArgs | Format-List | Out-String)"
    $terminateFlag = $true
    # *Return* a value that indicates whether watching should be stopped.
    # This value is later retrieved via Receive-Job.
    return $terminateFlag
  }

  # Subscribe to the watcher's Created events, which returns an event job.
  # This indefinitely running job receives the output from the -Action script
  # block whenever the latter is called after an event fires.
  $eventJob = Register-ObjectEvent $watcher Created -Action $action

  # Start watching:
  # Note: Not strictly necessary, because, curiously, 
  #       Register-ObjectEvent has aleady done this for us.
  $watcher.EnableRaisingEvents = $true 

  # Using an aux. background job, create a sample file that will trigger the 
  # watcher, after a delay.
  $tempFile = Join-Path $dir "$PID.tmp"
  $auxJob = Start-Job { Start-Sleep 3; 'hi' > $using:tempFile }

  Write-Host "Watching $dir for creation of $($watcher.Filter) files..."

  # Wait in a loop until the action block is run in response to an event and
  # produces $true as output to signal the intent to terminate, via Receive-Job.
  while ($true -ne (Receive-Job $eventJob)) {
    write-host . -NoNewline
    Start-Sleep -Milliseconds 500  # sleep a little
  }

}
finally {
  # Clean up.
  # Dispose of the watcher.
  $watcher.Dispose() 
  # Remove the event job (and with it the event subscription).
  $eventJob | Remove-Job -Force 
  # Clean up the helper job.
  Remove-Job -ea Ignore -Force $auxJob 
  # Remove the temp. file
  Remove-Item -ea Ignore $tempFile
}