design-patterns - Powershell脚本: recommended way to implement ShouldProcess when function calls are nested?

测试脚本:

function outer
{
    [cmdletbinding(supportsshouldprocess=$true)]
    param($s)

    process
    {
        $pscmdlet.shouldprocess("outer $s", "ShouldProcess") | out-null
        "" | out-file "outer $s"

        inner ImplicitPassthru
        inner VerbosePassthru -Verbose:$Verbose
        inner WhatifPassthru -WhatIf:$WhatIf
    }
}

function inner
{
    [cmdletbinding(supportsshouldprocess=$true)]
    param($s)

    process
    {
        $pscmdlet.shouldprocess("inner $s", "ShouldProcess") | out-null
        "" | out-file "inner $s"
    }
}

"`n** NORMAL **"
outer normal
"`n** VERBOSE **"
outer verbose -Verbose
"`n** WHATIF **"
outer whatif -WhatIf

输出:

** NORMAL **
VERBOSE: Performing operation "ShouldProcess" on Target "inner VerbosePassthru".
What if: Performing operation "ShouldProcess" on Target "inner WhatifPassthru".
What if: Performing operation "Output to File" on Target "inner WhatifPassthru".

** VERBOSE **
VERBOSE: Performing operation "ShouldProcess" on Target "outer verbose".
VERBOSE: Performing operation "ShouldProcess" on Target "inner VerbosePassthru".
What if: Performing operation "ShouldProcess" on Target "inner WhatifPassthru".
What if: Performing operation "Output to File" on Target "inner WhatifPassthru".

** WHATIF **
What if: Performing operation "ShouldProcess" on Target "outer whatif".
What if: Performing operation "Output to File" on Target "outer whatif".
What if: Performing operation "ShouldProcess" on Target "inner ImplicitPassthru".
What if: Performing operation "Output to File" on Target "inner ImplicitPassthru".
What if: Performing operation "ShouldProcess" on Target "inner VerbosePassthru".
What if: Performing operation "Output to File" on Target "inner VerbosePassthru".
What if: Performing operation "ShouldProcess" on Target "inner WhatifPassthru".
What if: Performing operation "Output to File" on Target "inner WhatifPassthru".

在我看来，这里有几个怪异之处:

指定-WhatIf:$ foo将始终打开在被叫方(及其被叫方)中的$ WhatIf，无论$ foo是什么。

当您确实指定-WhatIf为“真”(不将其限制为现有变量)时，它将隐式传播到被调用者。无需直通或喷溅。

与-WhatIf不同，显式-Verbose不会隐式地级联到被调用方。

当您尝试手动传递-Verbose:$ foo时，您的行为确实类似于-WhatIf:$ foo。但这只会影响手动测试$ psCmdlet.ShouldProcess()的脚本-内置cmdlet不受影响。

N.B. :确认行为与WhatIf相同。为简洁起见，我省略了它。

在网络上搜索和连接，我几乎看不到与高级功能有关的ShouldProcess行为(赞成或反对)的深入讨论。最近的是a post from James O'Neill，建议在整个调用堆栈中传递$ psCmdlet的单个实例。但是，他这样做是为了解决一个完全不同的问题(避免使用多个-Confirm提示)。同时，当您坚持为每个函数提供标准的$ psCmdlet时，我看不到任何有关预期结果的文档……更少的设计模式，最佳实践等……

最佳答案

您实际上不能引用$ WhatIf或$ Verbose，因为它们是为您合成的，即这些变量在您的函数中不存在。如果用户指定了它们，则可以通过$ PSBoundParameters获得它们，但如果用户未指定，则显然它们将不在此哈希表中。

当您将值传递给交换机时，PowerShell将执行典型的强制过程，尝试将指定的值转换为 bool(boolean) 值。由于未定义$ whatif，因此将其评估为$ null，这将导致switch值设置为$ true。据推测，这是因为它看到该开关实际上是明确指定为无值的，这等效于仅指定-Whatif为无值。跟踪参数绑定(bind)时可以看到以下内容:

function Foo
{
    [CmdletBinding(SupportsShouldProcess=1)]
    param()

    Process
    {
        $PSBoundParameters
    }
}

Trace-Command -name ParameterBinding -expr {Foo -whatif:$xyzzy} -PSHost
DEBUG: BIND NAMED cmd line args [Foo]
DEBUG:   BIND arg [] to parameter [WhatIf]
DEBUG:     COERCE arg to [System.Management.Automation.SwitchParameter]
DEBUG:       Arg is null or not present, type is SWITCHPARAMTER, value is true.
DEBUG:         BIND arg [True] to param [WhatIf] SUCCESSFUL
DEBUG: BIND POSITIONAL cmd line args [Foo]
DEBUG: MANDATORY PARAMETER CHECK on cmdlet [Foo]
DEBUG: CALLING BeginProcessing
DEBUG: CALLING EndProcessing

$ WhatIfPreference和$ VerbosePreference可以根据是否使用-verbose或-whatif调用external来适当设置。我可以看到那些值传播到内部就好了。似乎$ pscmdlet.ShouldProcess存在PowerShell错误。在这种情况下，它似乎不符合$ VerbosePreference的值。您可以尝试将-Verbose传递给inner，如下所示:

inner VerbosePassthru -Verbose:($VerbosePreference -eq 'Continue')

另一个选择是使用Get-Variable -Scope，如下所示:

function Outer
{
    [CmdletBinding(SupportsShouldProcess=1)]
    param()

    Process
    {
        $pscmdlet.ShouldProcess("Outer process", '') > $null
        inner
        #inner -Verbose:($VerbosePreference -eq 'Continue')
    }
}

function Inner
{
    [CmdletBinding(SupportsShouldProcess=1)]
    param()

    Process
    {
        $pscmdlet = (Get-Variable -Scope 1 -Name PSCmdlet).Value
        $pscmdlet.ShouldProcess("Inner process", '') > $null
        "Inner $VerbosePreference"
    }
}

Outer -Verbose

我不确定我喜欢这样，因为这意味着您知道外层比内层高1级。您可以“遍历”作用域堆栈，以在堆栈中查找下一个PSCmdlet变量。这有效地消除了必须传递PSCmdlet(这是很麻烦的)，但这仍然是一个hack。您应该考虑为此在MS Connect上提交错误。