Check for parameter in function – accept input value 0

September 2, 2022

I’m trying to validate if a parameter is present, see example code:

function Test-Function {

    [CmdletBinding()]
    Param (
        [Parameter(Mandatory = $false)]
        [ValidateNotNullOrEmpty()]
        [Int64]$TestParam
    )
    if ($TestParam) {
       Write-Host "Parameter is present.."
       # Do stuff ...
    }
}

# Execute the function
Test-Function -TestParam 1
Parameter is present..

# Pass the value 0
Test-Function -TestParam 0
<no output>

Is there a way to fix this? The type must be an integer, not [String]

>Solution :

Use the $PSBoundParameters automatic variable to inspect parameter binding results for the current invocation:

if($PSBoundParameters.ContainsKey('TestParam')){
    "Caller definitely provided an argument for -TestParam"
}

Note that an argument is considered bound regardless of whether the binding was positional or if it was explicitly bound by name:

function f {
  param(
    [Parameter(Position = 0)]
    $TestParam
  )

  if($PSBoundParameters.ContainsKey('TestParam')){
    "Caller definitely provided an argument for -TestParam"
  }
}

PS ~> f -TestParam 123
Caller definitely provided an argument for -TestParam

PS ~> f 123
Caller definitely provided an argument for -TestParam

In the second example, we never explicitly bind 123 to -TestParam, but because TestParam is the first positional parameter, 123 is bound to $TestParam, and thus $PSBoundParameters.ContainsKey('TestParam') returns $true