解释 Powershell [void] 行为 [英] Explain Powershell [void] behavior

问题描述

我的脚本将一些信息从 Sharepoint 站点导出到 .CSV 文件.

My script exports some information from Sharepoint sites to a .CSV file.

# Enter Web Application URL
$WebAppURL="http://server"

# Enter Path to CSV-file
$CSVFilePath="Path"

$SiteCollections = Get-SPWebApplication $WebAppURL | Get-SPSite -Limit All

$Tree = foreach ($Site in $SiteCollections) {
    foreach ($Web in $Site.AllWebs) {
    $Groups = New-Object System.Collections.ArrayList
        foreach ($Group in $web.Groups) {
            [void]$Groups.Add($Group.Name)
        }

        $Groups = $Groups -join ','
        [PSCustomObject]@{
            Url = $web.URL
            Title = $web.Title
            CountOfLists= $web.Lists.Count
            PermissionsInherited = $web.Permissions.Inherited
            Groups = $Groups
            }
    }
}

$Tree | Export-CSV $CSVFilePath -NoTypeInformation -Encoding UTF8

如果我在 $Groups.Add($Group.Name) 之前使用 [void] 它可以正常工作，但没有 [void]，脚本返回一个空的 .CSV 文件.

If I use [void] before $Groups.Add($Group.Name) it works correctly, but without [void], the script returns an empty .CSV file.

为什么会发生这种情况?

Why does this happen?

推荐答案

• PowerShell 隐式输出既没有在变量中捕获的值，也没有被抑制(如 [void] (...), $null= ... 或 Out-Null)，重定向(使用 >/>>>)，也不发送通过管道 (|) 到另一个命令.

  • PowerShell implicitly outputs values that are neither captured in a variable, suppressed (as with [void] (...), $null = ..., or Out-Null), redirected (with > / >>), nor sent through the pipeline (|) to another command.

    • 有关此行为背后的设计原理，请参阅此答案的底部部分.
    • See the bottom section of this answer for the design rationale behind this behavior.

    $Groups.Add($Group.Name) 输出一个 [int] (System.Int32) 值(新附加元素的索引)，所以没有 [void] 强制转换这个整数首先成为内部然后外部 foreach 循环的输出^[1] 的一部分，从而有效地成为第一个输出对象在 $Tree 中捕获.

    $Groups.Add($Group.Name) outputs an [int] (System.Int32) value (the index of the newly appended element), so without the [void] cast this integer becomes part of first the inner and then the outer foreach loop's output^[1], and thereby effectively the very first output object captured in $Tree.

    当管道对象到导出时-Csv，它是 第一个 对象，它根据该对象的(公共)属性确定要导出的列.

    When piping objects to Export-Csv, it is the first object alone that determines what columns to export, based on that object's (public) properties.

    [int] 实例本身只是一个值，它没有任何属性，因此生成的 CSV 文件实际上是空的.

  An [int] instance is just a value itself, it doesn't have any properties, so the resulting CSV file is effectively empty.

  ^{[1] System.Collections.ArrayList 的通用等效项是 System.Collections.Generic.List`1，其.Add()方法不不返回一个值，这就是为什么它在PowerShell中(和一般情况下)使用更可取的原因.等效的构造调用将是:
  $Groups = New-Object System.Collections.Generic.List[object] 或者，在 PSv5+ 中，
  $Groups = [System.Collections.Generic.List[object]]::new()}

  ^{[1] The generic equivalent of System.Collections.ArrayList is System.Collections.Generic.List`1, whose .Add() method does not return a value, which is why its use is preferable in PowerShell (and generally). The equivalent construct call would be:
  $Groups = New-Object System.Collections.Generic.List[object] or, in PSv5+,
  $Groups = [System.Collections.Generic.List[object]]::new()}

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