windows - 无法覆盖变量，因为它是只读的

Question

我正在尝试学习 Powershell。我有以下脚本:

$cmd = {
  param($pid)
  Write-Host $pid
}

$processes = Get-Process -Name notepad
foreach ($process in $processes) 
{ 
    $pid = $process.ID
    Start-Job -ScriptBlock $cmd -ArgumentList $pid
}

我收到以下错误:

Cannot overwrite variable PID because it is read-only or constant. At line:7 char:1 + $pid = 1 + ~~~~~~~~ + CategoryInfo : WriteError: (PID:String) [], SessionStateUnauthorizedAccessException + FullyQualifiedErrorId : VariableNotWritable Cannot overwrite variable PID because it is read-only or constant. At line:11 char:1 + $pid = $process.ID + ~~~~~~~~~~~~~~~~~~ + CategoryInfo : WriteError: (PID:String) [], SessionStateUnauthorizedAccessException + FullyQualifiedErrorId : VariableNotWritable Start-Job : Cannot overwrite variable pid because it is read-only or constant. At line:12 char:5 + Start-Job -ScriptBlock $cmd -ArgumentList $pid

我在这里做错了什么？

Answer 1

$PID 是一个 reserved, automatic variable包含 session 的进程 ID。你不能设置它。

参见:

Get-Help about_Automatic_Variables 

有关自动变量的完整列表和说明。

编辑:

输出所有记事本进程的进程ID:

 Get-Process -Name notepad |
   Select -ExpandProperty ID