Dynamic parameters must be accessed using the PSBoundParameters variable within a function or script; dynamic parameters do not initialize variables of their own.

The value of the Action parameter used in the previous examples must be retrieved by using Action as a key, shown as follows:

using namespace System.Management.Automation

function Test-DynamicParam {
    [CmdletBinding()]
    param ( )

    dynamicparam {
        $paramDictionary = [RuntimeDefinedParameterDictionary]::new()

        $parameter = [RuntimeDefinedParameter]::new('Action', [String], [Attribute[]]@(
                [Parameter]@{ Mandatory = $true; Position = 1 }
                [ValidateSet]::new('Start', 'Stop', 'Create', 'Delete')
            )
        )
        $paramDictionary.Add($parameter.Name, $parameter)

        $paramDictionary
    }

    end {
        Write-Host $psboundparameters['Action']
    }
}

As with parameters from the param block, the $psboundparameters.ContainsKey method may be used to find out whether a user has specified a value for the parameter. Dynamic parameters cannot have a default value; any default values must be created in begin, process, or end.

A dynamic parameter that accepts pipeline input, like a normal parameter that accepts pipeline input, will only have a value within the process and end blocks. The end block will only see the last value in the pipeline. The following example demonstrates this:

using namespace System.Management.Automation

function Test-DynamicParam {
    [CmdletBinding()]
    param ( )

    dynamicparam {
        $paramDictionary = [RuntimeDefinedParameterDictionary]::new()

        $parameter = [RuntimeDefinedParameter]::new('InputObject', [String], [Attribute[]]@(
                [Parameter]@{ Mandatory = $true; ValueFromPipeline = $true }
            )
        )
        $paramDictionary.Add($parameter.Name, $parameter)

        $paramDictionary
    }

    begin {
        'BEGIN: Input object is present: {0}' -f @(
            $psboundparameters.ContainsKey('InputObject')
        )
    }

    process {
        'PROCESS: Input object is present: {0}; Value: {1}' -f @(
            $psboundparameters.ContainsKey('InputObject')
            $psboundparameters['InputObject']
        )
    }

    end {
        'END: Input object is present: {0}; Value: {1}' -f @(
            $psboundparameters.ContainsKey('InputObject')
            $psboundparameters['InputObject']
        )
    }
}

The function can be used with arbitrary input values, for example:

PS> 1..2 | Test-DynamicParam
BEGIN: Input object is present: False
PROCESS: Input object is present: True; Value: 1
PROCESS: Input object is present: True; Value: 2
END: Input object is present: True; Value: 2

The PSBoundParameters variable, and any other parameters, may be referenced inside the dynamicparam block.