Get-DefaultParameterValue.ps1

function Get-DefaultParameterValue {
    <#
    .SYNOPSIS
        Returns name and default value for parameters of given command or
        scriptblock.
    .DESCRIPTION
        Returns names of parameters along with their default values for given
        command or scriptblock.
    .NOTES
        This only works for functions written in PowerShell. This will not work
        for commands in binary modules.
    .EXAMPLE
       $sb = { param ($a = 1, $b, $c) $a + 1 }
       Get-DefaultParameterValue $sb
    .EXAMPLE
        function foo
        {
            param
            (
                $a = 1, $b, $c
            )

            $a + 1
        }

        Get-DefaultParameterValue -Command (Get-Command foo)
    .EXAMPLE
        Get-DefaultParameterValue -Command (Get-Command Get-Variable)
    #>
    [Cmdletbinding(DefaultParameterSetName = 'ScriptBlock', PositionalBinding = $false)]
    param
    (
        [ValidateNotNull()]
        [Parameter(ParameterSetName = 'ScriptBlock', Mandatory = $true, Position = 0)]
        [ScriptBlock] $ScriptBlock,

        [ValidateNotNull()]
        [Parameter(ParameterSetName = 'Command', Mandatory = $true)]
        [System.Management.Automation.CommandInfo] $Command
    )

    switch ($PSCmdlet.ParameterSetName) {
        'ScriptBlock' {
            $ScriptBlock.Ast.ParamBlock.Parameters |
                Where-Object DefaultValue |
                Select-Object Name, DefaultValue
        }
        'Command' {
            $Command.ScriptBlock.Ast.Body.ParamBlock.Parameters |
                Where-Object DefaultValue |
                Select-Object Name, DefaultValue
        }
    }
}