在脚本块中使用开始、处理、结束

Question

是否可以在脚本块中使用高级功能特性Begin, Process, End？

例如，我有以下脚本块：

$startStopService = {
Param(
    [bool] $startService)    

  if ($startService){
     ...
     Start-Service "My-Service"
  }
  else {
     Stop-Service "My-Service"
  }
}

因为我希望能够控制脚本块的详细输出，所以我想将块更改为：

$startStopService = {
Param(
    [bool] $startService)    

  Begin {
     $oldPreference = $VerbosePreference 
     $VerbosePreference = $Using:VerbosePreference
  }
  Process {
     if ($startService){
        ...
        Start-Service "My-Service"
     }
     else {
        Stop-Service "My-Service"
     }
  }
  End {
     # Restore the old preference
     $VerbosePreference = $oldPreference 
  }
}

是否可以在此处使用Begin, Process, End，尽管脚本块不是 cmdlet？我只是希望VerbosePreference 恢复到旧值，无论是否发生错误。当然我可以使用try{}finally{} 作为替代，但我发现Begin, Process, End 更直观。

谢谢

Answer 1

这是可能的，如about_script_blocks中所述：

与函数一样，脚本块可以包含 DynamicParam、Begin、 处理和结束关键字。有关详细信息，请参阅 about_Functions 和 about_Functions_Advanced。

---

为了测试这一点，我修改了你的脚本块并运行了这个：

$startStopService = {
Param(
    # a bool needs $true or $false passed AFAIK
    # A switch is $true if specified, $false if not included
    [switch] $startService 
 )    

  Begin {
     $oldPreference  = $VerbosePreference 
     Write-Output "Setting VerbosePreference to Continue"

     # $Using:VerbosePreference gave me an error
     $VerbosePreference = "Continue"
  }
  Process {
     if ($startService){
        Write-Verbose "Service was started"
     }
     else {
        Write-Verbose "Service was not started"
     }
  }
  End {
     # Restore the old preference
     Write-Output "Setting VerbosePreference back to $oldPreference"
     $VerbosePreference = $oldPreference 
  }

}

Write-Verbose "This message will not print if VerbosePreference is the default SilentlyContinue"

. $startStopService -startService

Write-Verbose "This message will not print if VerbosePreference is the default SilentlyContinue"

---

您追求什么功能？如果您想在运行脚本块时打印详细消息但不更改脚本其余部分中的$VerbosePreference，请考虑使用[CmdletBinding()] 和-Verbose 标志：

$startStopService = {
    [CmdLetBinding()]
    Param(
        [switch] $startService
    )

     Write-Verbose "This is a verbose message"

}
Write-Verbose "This message will not print if VerbosePreference is the default SilentlyContinue"

. $startStopService -verbose

Write-Verbose "This message will not print if VerbosePreference is the default SilentlyContinue"

---

编辑 - 调用命令

在您发表评论后，我正在研究Invoke-Command 的功能。并且发现很多东西都不行。

我认为对您最有用的简短版本：您可以在脚本块中声明$VerbosePreference = "Continue"，这将仅限于脚本块的范围。以后不用改回来了。

$startStopService = {
    [CmdLetBinding()]
    Param(
        [parameter(Position=0)]
        [switch]$startStopService,

        [parameter(Position=1)]
        [switch]$Verbose
    )

    if($Verbose){
        $VerbosePreference = "Continue"
    }

    Write-Verbose "This is a verbose message"

}

Write-output "VerbosePreference: $VerbosePreference"
Write-Verbose "This message will not print if VerbosePreference is the default SilentlyContinue"

Invoke-Command -Scriptblock $startStopService -ArgumentList ($true,$true)

Write-output "VerbosePreference: $VerbosePreference"
Write-Verbose "This message will not print if VerbosePreference is the default SilentlyContinue"

试图将-Verbose 开关CommonParameter 传递给Invoke-Command 是不行的。这使用标准的Verbose 开关参数，允许您传递$true/$false（或省略）来控制详细输出。

_{相关：
about_Functions
about_Functions_Advanced}