如何不传播 -WhatIf 和 -Confirm？

Question

Powershell 的默认行为似乎是将 -WhatIf 和 -Confirm 传播到从使用 -WhatIf 或 -Confirm 调用的函数中调用的所有函数。

但是如果（双关语）我不想要那个怎么办？如果我只想保护在我的系统上执行实际更改的代码而不是我的其余代码怎么办？

这是一个例子：

function Set-Something {
    [CmdletBinding(SupportsShouldProcess = $true, ConfirmImpact = 'Medium')]
    [OutputType([string])] 

    Param (
        [Parameter(Mandatory = $false, ValueFromPipeline = $true)]
        [string] $ComputerName = $env:COMPUTERNAME
    )

    Process {
        New-Item -Path "beforeChange" -Type File | Out-Null
        Remove-Item -Path "beforeChange" -ErrorAction SilentlyContinue

        # Here is the bit of code that needs to be "protected"
        if ($PSCmdlet.ShouldProcess($ComputerName, "Do something")) {
            # Actually do something on $ComputerName
            New-Item -Path "inChange" -Type File | Out-Null
            Remove-Item -Path "inChange" -ErrorAction SilentlyContinue
        }

        New-Item -Path "afterChange" -Type File | Out-Null
        Remove-Item -Path "afterChange" -ErrorAction SilentlyContinue
    }
}

"-"*50 + "Set-Something -WhatIf" + "-"*50 
Set-Something -WhatIf
"-"*50 + "Set-Something -Confirm" + "-"*50 
Set-Something -Confirm

Set-Something 函数仅在受保护位中执行系统更改内容。它也使用临时文件，但 New-Item 和 Remove-Item 不应触发 WhatIf 或 Confirm。不幸的是，它不是这样工作的：

--------------------------------------------------Set-Something -WhatIf--------------------------------------------------
What if: Performing the operation "Create File" on target "Destination: C:\Users\GO7\beforeChange".
What if: Performing the operation "Do something" on target "GEOCED".
What if: Performing the operation "Create File" on target "Destination: C:\Users\GO7\afterChange".

我可以将-WhatIf:$false -Confirm:$false 添加到每个支持 ShouldProcess 的函数中，但这会很乏味。

所以到目前为止我所做的是：

1. 将 $WhatIfPreference 和 $ConfirmPreference 保存在我的函数顶部
2. 将这些首选项重置为默认值
3. 在受保护的块之前恢复保存的首选项
4. 在块内和块外再次重置首选项

像这样：

function Set-Something2 {
    [CmdletBinding(SupportsShouldProcess = $true, ConfirmImpact = 'Medium')]
    [OutputType([string])] 

    Param (
        [Parameter(Mandatory = $false, ValueFromPipeline = $true)]
        [string] $ComputerName = $env:COMPUTERNAME
    )

    Begin {
        # Save the ShouldProcess parameters for later use
        $WhatIfPref = $WhatIfPreference
        $ConfirmPref = $ConfirmPreference

        # Reset ShouldProcess parameters to their default value
        $WhatIfPreference = 0
        $ConfirmPreference = 'High'
    }

    Process {
        New-Item -Path "beforeChange" -Type File | Out-Null
        Remove-Item -Path "beforeChange" -ErrorAction SilentlyContinue

        # We restore the previously saved ShouldProcess parameters just before the "protected" bit of code
        $WhatIfPreference = $WhatIfPref
        $ConfirmPreference = $ConfirmPref

        # Here is the bit of code that needs to be "protected"
        if ($PSCmdlet.ShouldProcess($ComputerName, "Do something")) {
            # Inside the protected bit, we reset ShouldProcess parameters to their default value
            $WhatIfPreference = 0
            $ConfirmPreference = 'High'

            # Actually do something on $ComputerName
            New-Item -Path "inChange" -Type File | Out-Null
            Remove-Item -Path "inChange" -ErrorAction SilentlyContinue
        }

        # After the protected bit, we reset ShouldProcess parameters to their default value
        $WhatIfPreference = 0
        $ConfirmPreference = 'High'

        New-Item -Path "afterChange" -Type File | Out-Null
        Remove-Item -Path "afterChange" -ErrorAction SilentlyContinue
    }
}

"-"*50 + "Set-Something2 -WhatIf" + "-"*50 
Set-Something2 -WhatIf
"-"*50 + "Set-Something2 -Confirm" + "-"*50 
Set-Something2 -Confirm

结果如我所愿：

--------------------------------------------------Set-Something2 -WhatIf--------------------------------------------------
What if: Performing the operation "Do something" on target "GEOCED".
--------------------------------------------------Set-Something2 -Confirm--------------------------------------------------

Confirm
Are you sure you want to perform this action?
Performing the operation "Do something" on target "GEOCED".
[Y] Yes  [A] Yes to All  [N] No  [L] No to All  [S] Suspend  [?] Help (default is "Y"):

但是我应该这样做吗？我觉得它不是很优雅...

Answer 1

您的问题似乎与范围有关。运行它并阅读文档：

help about_Scopes

您可以在作用域中更改首选项变量（例如，$ConfirmPreference），但这不会影响其在父作用域中的值。这是一个简短的例子：

PS C:\Scripts> $ConfirmPreference
High
PS C:\Scripts> Get-Content .\Test-Preference.ps1
$ConfirmPreference = "Low"
$ConfirmPreference
PS C:\Scripts> .\Test-Preference.ps1
Low
PS C:\Scripts> $ConfirmPreference
High

从这个简短的示例中可以看出，一旦范围（即脚本）终止，首选项变量会自动恢复为之前的值。

如果要在当前范围内执行新范围，可以使用 & 运算符调用脚本块。示例：

$ConfirmPreference

# execute a scriptblock (create new scope, change preference variable)
& {
  $ConfirmPreference = "Low"
  $ConfirmPreference
}

$ConfirmPreference

如果你把以上几行放在一个脚本文件中并运行它，输出将是：

High
Low
High

Answer 2

为了在我不希望传递 -WhatIf 的特定函数上解决此问题，我将其明确设置为 $false。

例如，来自需要设置订阅上下文以便以后只读查询正常工作的 Azure 脚本：

Set-AzContext -Subscription $Subscription -WhatIf:$false

这可以防止Set-AzContext 从我的主脚本继承-WhatIf，但仍然允许我稍后有选择地使用$PSCmdlet.ShouldProcess() 进行更危险的更改。