电源外壳.无法从{}获取变量 [英] PowerShell. Can't get variable from {}

问题描述

在下面的代码中，有一个名为"$ action" = {...}的参数.在方括号内有一些变量($ path，$ logPath等)，如何从括号"{}"之外的该参数访问变量?我需要一个函数("RunFunctions")的结果进行while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{}表示法的某些信息的地方吗?谢谢.

In the code below there is a parameter named "$action" = {...}. Inside the brackets there are some variables ($path, $logPath, etc.) How can I access variables from this parameter outside of the braces "{}"? I need result of one of my functions("RunFunctions") for a while loop. Or if it's some stupid question please can you point me to the place where I can find some information about this {} notation? Thanks.

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 $_
}

推荐答案

{ ... }是脚本块(字面意思)-可重用的PowerShell代码片段，您可以按需执行(例如函数指针或其他语言的委托.)

{ ... } is a script block (literal) - a reusable piece of PowerShell code that you can execute on demand (like a function pointer or delegate in other languages).

通过将存储在变量$action中的此类块传递给Register-ObjectEvent -Action，PowerShell会在感兴趣的事件触发时调用它，并在动态模块中进行调用，该模块的作用域完全是与呼叫者分开.

By passing such a block, stored in variable $action, to Register-ObjectEvent -Action, PowerShell invokes it whenever the event of interest fires, and does so in a dynamic module, whose scope is entirely separate from the caller's.

因此，您的调用代码看不到在该块内部创建的变量，因为它们是该块的本地变量.

Therefore, your calling code doesn't see the variables created inside the block, as they are local to that block.

^{有关PowerShell中作用域的更多信息，请参见此答案的底部.}

^{For more information about scopes in PowerShell, see the bottom section of this answer.}

虽然PowerShell通常 允许您在 other 范围内创建和修改变量，但是如果您采取显式操作，则不是使用Register-ObjectEvent -Action，因为动态模块的作用域从根本上不能访问调用者的作用域，而只能访问 global 作用域.

While PowerShell generally lets you create and modify variables in other scopes as well, if you take explicit action, this is not an option with Register-ObjectEvent -Action, because a dynamic module's scope fundamentally doesn't have access to the caller's scope, only to the global scope.

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

但是，最好避免使用全局范围，因为即使脚本退出后，全局变量仍然存在(它们是 session -global).

However, using the global scope is best avoided, because global variables linger even after the script exits (they are session-global).

更好的解决方案是:

• 使动作脚本块 output 为调用者的值.

使用事件作业
，使调用者通过Receive-Job接收该输出. Register-ObjectEvent -Action返回.

have the caller receive that output via Receive-Job, using the event job that
Register-ObjectEvent -Action returns.

这是一个简化的，独立的示例，演示了该技术:

Here's a simplified, self-contained example that demonstrates the technique:

它设置了一个观察程序，附加了一个事件处理程序，并创建了一个触发观察程序事件的文件.

It sets up a watcher, attaches an event handler, and creates a file that triggers a watcher event.

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
}

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