接受位置绑定参数作为参数的函数，但也来自管道

Question

我正在尝试创建一个接受管道位置绑定参数和位置绑定参数的日志记录函数。但是，我使用以下代码不断收到此错误：

Function Test
{
[CmdletBinding(SupportsShouldProcess,DefaultParameterSetName='def')]
Param(
  [Parameter(Position=0,ParameterSetName='def')]
  [String]$Pos1,
  [Parameter(ValueFromPipeline,Position=1,ParameterSetName='pip')]
  [String]$InputObject,
  [Parameter(Position=1,ParameterSetName='def')]
  [Parameter(Position=0,ParameterSetName='pip')]
  [String]$State
)
    Process
    {
        Switch ($PScmdlet.ParameterSetName)
        {
            'def' {Write-Host "${State}: $Pos1"}
            'pip' {Write-Host "${State}: $InputObject"}
        }
    }
}

PS C:\> 'this' | Test 'error'

test : The input object cannot be bound to any parameters for the command either because the command does not take pipeline input or the input and its properties do not match any of the parameters that take pipeline input.
At line:1 char:10
+ 'test' | test 'error'
+          ~~~~~~~~~~~~
    + CategoryInfo          : InvalidArgument: (test:String) [Test], ParameterBindingException
    + FullyQualifiedErrorId : InputObjectNotBound,Test

我可以让函数的位置绑定管道调用与以下示例一起使用：

Function Test
{
Param(
  [Parameter(Position=1,ValueFromPipeline)]
  [String]$Msg,
  [Parameter(Position=0)]
  [String]$State
)

    Process
    {
        Write-Host "${State}: $Msg"
    }
}

PS C:\> 'this' | Test 'error'
error: this

所以我的问题是：如何创建一个函数，该函数将在命令行 (Test 'message' 'status') 和管道 ('message' | Test 'status') 中获取位置绑定的参数，而无需显式调用参数名称 ('message' | Test -State 'status' )?

Answer 1

让我们用后面脚本中的以下代码 sn-p 替换 Process { Write-Host "${State}: $Msg" } 块，以生成更具指导性的输出并从中获取信息：

Process
{
    ###  Write-Host "${State}: $Msg"
    Write-Host "State=$State`t Msg=$Msg" -NoNewline
    Write-Host "`t`t`t`t$($MyInvocation.Line.trim())" -ForegroundColor Cyan
}

然后，检查 输出 以了解（几乎）所有可能的参数组合：

PS D:\PShell> 
'this' | Test    -State 'error'
'this' | Test           'error'
Test -Msg 'this' -State 'error'
Test -Msg 'this'        'error'
Test      'this' -State 'error'
Test      'this'        'error'

State=error  Msg=this               'this' | Test    -State 'error'
State=error  Msg=this               'this' | Test           'error'
State=error  Msg=this               Test -Msg 'this' -State 'error'
State=error  Msg=this               Test -Msg 'this'        'error'
State=error  Msg=this               Test      'this' -State 'error'
State=this   Msg=error              Test      'this'        'error'

PS D:\PShell> 

我们可以看到Test 'this' 'error' 的不同输出（没有管道和行中没有明确命名的参数）。因此，Test 'error' 'this' 可以给出“正确”的结果。

另一种方法：让我们改变脚本输出如下：

Function Test
{
Param(
  [Parameter(Position=1,ValueFromPipeline)]
  [String]$Msg,
  [Parameter(Position=0)]
  [String]$State
)
    Process
    {
        #Write-Host "${State}: $Msg"
        $auxLine = $MyInvocation.Line.split( ' ', 
                [System.StringSplitOptions]::RemoveEmptyEntries)
        if ( $auxLine[0] -eq $MyInvocation.InvocationName -and
                '-Msg'   -notin $auxLine -and
                '-State' -notin $auxLine ) 
        {
            Write-Host "State=$Msg`t Msg=$State" -NoNewline
            Write-Host "`tALTERED`t`t$($MyInvocation.Line.trim())" -ForegroundColor Yellow
        } else {
            Write-Host "State=$State`t Msg=$Msg" -NoNewline
            Write-Host "`t`t`t`t$($MyInvocation.Line.trim())" -ForegroundColor Cyan
        }
    }
}

输出：

PS D:\PShell> 
'this' | Test    -State 'error'
'this' | Test           'error'
Test -Msg 'this' -State 'error'
Test -Msg 'this'        'error'
Test      'this' -State 'error'
Test      'this'        'error'

State=error  Msg=this               'this' | Test    -State 'error'
State=error  Msg=this               'this' | Test           'error'
State=error  Msg=this               Test -Msg 'this' -State 'error'
State=error  Msg=this               Test -Msg 'this'        'error'
State=error  Msg=this               Test      'this' -State 'error'
State=error  Msg=this   ALTERED     Test      'this'        'error'

PS D:\PShell>