Function that accepts position-bound parameters as arguments, but also from pipeline

user_8188846 0
Viewed 164

I'm attempting to create a logging function that accepts pipeline positionally-bound parameters, and positionally-bound arguments. However, I keep getting this error with the following code:

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

I can get the position-bound pipeline calling of the function to work with the following example:

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

So my question: how can I create a function that will take positionally-bound arguments at command line (Test 'message' 'status') and from the pipeline ('message' | Test 'status') without the need to explicitly call the parameter name ('message' | Test -State 'status')?

powershell-5.0 pipeline powershell
1 Answers

Let's replace the Process { Write-Host "${State}: $Msg" } block with the following code snippet in the latter script to make more instructive output and get over info from it:

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

Then, check output for (almost) all possible combinations of arguments:

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>

We can see different output for Test 'this' 'error' (no pipeline and no explicitly named parameters in the line). Therefore, Test 'error' 'this' could give "right" result.

Another approach: let's alter the script output as follows:

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
        }
    }
}

Output:

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>
user_34394040
Related