PowerShell:位置参数和 ValueFromPipeline

Question

我有一个玩具问题，感觉应该很简单。我想要一个像 Join-Path 这样支持管道的功能。称之为构建路径。因此，这些语句(我的测试 1-4)应该是等价的:

Get-Location | Build-Path Test

Get-Location | Build-Path -Right Test

Build-Path -Left (Get-Location) -Right Test

Build-Path (Get-Location) Test

我已经尝试了很多东西，最接近的是我能得到这两个函数(互斥):

A:对两个值的明确立场；测试 1 失败

function Build-Path
(
    [Parameter(Mandatory=$true, Position=0, ValueFromPipeline=$true)]
    [String] $Left, 
    [Parameter(Mandatory=$true, Position=1)]
    [String] $Right
)
{
    Join-Path $Left $Right
}

B:管道参数上没有位置，Right的位置为0；未能通过测试 4

function Build-Path
(
    [Parameter(Mandatory=$true, ValueFromPipeline=$true)]
    [String] $Left, 
    [Parameter(Mandatory=$true, Position=0)]
    [String] $Right
)
{
    Join-Path $Left $Right
}

我尝试过以多种方式使用 ParameterSet(没有保存我的尝试)但没有成功，我现在有点难过。

想法？

Answer 1

这不能按您希望的方式工作。您的两个参数都是相同的数据类型，PowerShell 将使用它来绑定(bind)参数，然后再查看它是否进入管道，并尝试立即填充从 0 开始的位置。

我什至尝试用参数集重做它:

function Build-Path {
[CmdletBinding(DefaultParameterSetName='Default',PositionalBinding=$false)]
param(
    [Parameter(
        ParameterSetName='Default',
        Mandatory=$true, 
        ValueFromPipeline=$true
    )]
    [Parameter(
        ParameterSetName='LooseyGoosey',
        Mandatory=$true,
        Position=0
    )]
    [String] 
    $Left, 

    [Parameter(
        ParameterSetName='Default',
        Mandatory=$true, 
        Position=0
    )]
    [Parameter(
        ParameterSetName='LooseyGoosey',
        Mandatory=$true,
        Position=1
    )]
    [String] 
    $Right
)

    Join-Path $Left $Right
}

要查看 PowerShell 如何绑定(bind)参数，请使用 Trace-Command:

Trace-Command -Name ParameterBinding -Expression { Build-Path (Get-Location) Test } -Verbose -PSHost

无论您如何切分，都会遇到问题。没有 DefaultParameterSet？无法解析参数集。切换默认值？然后，您只需更改哪些调用有效或无效。

您也不能将 -Right 参数设为 [String[]] 数组，因为在绑定(bind)期间 PowerShell 将尝试强制转换，因此 [String ] 仍将被接受和绑定(bind)。

DEBUG: ParameterBinding Information: 0 : BIND NAMED cmd line args [Get-Location]
DEBUG: ParameterBinding Information: 0 : BIND POSITIONAL cmd line args [Get-Location]
DEBUG: ParameterBinding Information: 0 : BIND cmd line args to DYNAMIC parameters.
DEBUG: ParameterBinding Information: 0 : MANDATORY PARAMETER CHECK on cmdlet [Get-Location]
DEBUG: ParameterBinding Information: 0 : CALLING BeginProcessing
DEBUG: ParameterBinding Information: 0 : CALLING EndProcessing
DEBUG: ParameterBinding Information: 0 : BIND NAMED cmd line args [Build-Path]
DEBUG: ParameterBinding Information: 0 : BIND POSITIONAL cmd line args [Build-Path]
DEBUG: ParameterBinding Information: 0 :     BIND arg [C:\Users\Briantist] to parameter [Right]
DEBUG: ParameterBinding Information: 0 :         Executing DATA GENERATION metadata: [System.Management.Automation.ArgumentTypeConverterAttribute]
DEBUG: ParameterBinding Information: 0 :             result returned from DATA GENERATION: C:\Users\Briantist
DEBUG: ParameterBinding Information: 0 :         BIND arg [C:\Users\Briantist] to param [Right] SKIPPED
DEBUG: ParameterBinding Information: 0 :     BIND arg [C:\Users\Briantist] to parameter [Left]
DEBUG: ParameterBinding Information: 0 :         Executing DATA GENERATION metadata: [System.Management.Automation.ArgumentTypeConverterAttribute]
DEBUG: ParameterBinding Information: 0 :             result returned from DATA GENERATION: C:\Users\Briantist
DEBUG: ParameterBinding Information: 0 :         BIND arg [C:\Users\Briantist] to param [Left] SKIPPED
DEBUG: ParameterBinding Information: 0 :     BIND arg [C:\Users\Briantist] to parameter [Right]
DEBUG: ParameterBinding Information: 0 :         Executing DATA GENERATION metadata: [System.Management.Automation.ArgumentTypeConverterAttribute]
DEBUG: ParameterBinding Information: 0 :             result returned from DATA GENERATION: C:\Users\Briantist
DEBUG: ParameterBinding Information: 0 :         BIND arg [C:\Users\Briantist] to param [Right] SKIPPED
DEBUG: ParameterBinding Information: 0 :     BIND arg [C:\Users\Briantist] to parameter [Right]
DEBUG: ParameterBinding Information: 0 :         Executing DATA GENERATION metadata: [System.Management.Automation.ArgumentTypeConverterAttribute]
DEBUG: ParameterBinding Information: 0 :             result returned from DATA GENERATION: C:\Users\Briantist
DEBUG: ParameterBinding Information: 0 :         COERCE arg to [System.String]
DEBUG: ParameterBinding Information: 0 :             Parameter and arg types the same, no coercion is needed.
DEBUG: ParameterBinding Information: 0 :         BIND arg [C:\Users\Briantist] to param [Right] SUCCESSFUL
DEBUG: ParameterBinding Information: 0 :     BIND arg [Test] to parameter [Right]
DEBUG: ParameterBinding Information: 0 :         Executing DATA GENERATION metadata: [System.Management.Automation.ArgumentTypeConverterAttribute]
DEBUG: ParameterBinding Information: 0 :             result returned from DATA GENERATION: Test
DEBUG: ParameterBinding Information: 0 :         BIND arg [Test] to param [Right] SUCCESSFUL
DEBUG: ParameterBinding Information: 0 : MANDATORY PARAMETER CHECK on cmdlet [Build-Path]
DEBUG: ParameterBinding Information: 0 :     PROMPTING for missing mandatory parameters using the host