问题

在PowerShell中，gps | where {$_.mainwindowtitle} 这个命令用于列出所有具有打开窗口的正在运行的进程。您疑惑的部分是，这个命令首先列出所有正在运行的进程，然后根据条件 mainwindowtitle == True 进行筛选，但在gps (get-process) 或 tasklist 的输出中似乎没有名为 "mainwindowtitle" 的列。您是否理解代码的方式有误呢？

您的理解是正确的，gps 实际上是 Get-Process 命令的缩写，用于获取系统中的进程列表。然后，where {$_.mainwindowtitle} 是一个筛选条件，它只返回具有非空 mainwindowtitle 的进程，这意味着这些进程具有打开的窗口。

"mainwindowtitle" 列是 System.Diagnostics.Process 对象的属性，但默认情况下，在输出中并不显示这个属性。只有当您使用 Select-Object 命令来显式选择这个属性时，它才会在输出中显示。

如果您希望查看进程的 "mainwindowtitle" 属性，可以像这样修改命令：

gps | where {$_.mainwindowtitle} | Select-Object ProcessName, MainWindowTitle

这将显示具有打开窗口的进程的名称和窗口标题。

希望这能解答您的疑问。如有任何建议或问题，请随时提出。

答案1

得分: 1

以下是代码部分不需要翻译的内容：

The code works as expected, and - thanks to the separation between data and its display representation in PowerShell's object-based pipeline - can easily be adapted to show what you want:

• The System.Diagnostics.Process objects returned by Get-Process (whose built-in alias is gps) have a .MainWindowTitle property that Where-Object (whose built-in aliases are where and ?) filters by.

• However, the .MainWindowTitle property values are simply not displayed by default, because the formatting definitions for the output type do not define a display column for it (horizontal space in tables is limited, so only the most important properties are shown.

  • You can select your own display columns by passing the names of the properties of interest to Format-Table (whose built-in alias is ft):

# Find all processes that have a main-window title and 
# show their process ID, name, and main-window title in a table.
Get-Process | 
  Where-Object MainWindowTitle | 
  Format-Table -Property Id, Name, MainWindowTitle

The most concise equivalent of the above, using aliases (recommended for interactive use only):

gps | ? MainWindowTitle | ft Id, Name, MainWindowTitle

Note:

• Simplified syntax is used in the Where-Object call.

  • That is, MainWindowTitle is equivalent to passing script block { $_.MainWindowTitle }

  • Even though the .MainWindowTitle property contains strings, they are implicitly evaluated as Booleans ($true or $false) by Where-Object, simply based on whether they are empty ($false) or not ($true).
    That is, { $_.MainWindowTitle } is effectively the same as the more verbose { $_.MainWindowTitle -ne '' }
    For a summary of PowerShell's implicit to-Boolean coercion logic, see the bottom section of this answer.

• It is important to note that Format-* cmdlets should only ever be used for display formatting, and never to supply output for subsequent programmatic processing.

  • If you want to select a subset of properties as data, for later programmatic processing, use Select-Object (whose built-in alias is select) instead.

  • See this answer for more information.

# Find all processes that have a main-window title and 
# show their process ID, name, and main-window title in a table.
Get-Process | 
  Where-Object MainWindowTitle | 
  Format-Table -Property Id, Name, MainWindowTitle

gps | ? MainWindowTitle | ft Id, Name, MainWindowTitle