Display All Powershell Script Parameter Default Variables - powershell

Question

Say I have a Powershell script TestParameters.ps1 like this, with two mandatory, named parameters and two optional parameters:
[CmdletBinding()]
Param (
[Parameter(Mandatory=$True)]
[string] $AFile = "C:\A\Path",
[Parameter(Mandatory=$True)]
[ValidateSet("A","B","C", "D")]
[string] $ALetter = "A",
[Parameter(Mandatory=$False)]
[ValidateNotNullOrEmpty()]
[string] $Optional1 = "Foo",
[Parameter(Mandatory=$False)]
[ValidateNotNullOrEmpty()]
[string] $Optional2 = "Bar"
)
echo "Hello World!"
$psboundparameters.keys | ForEach {
Write-Output "($_)=($($PSBoundParameters.$_))"
}
Say I call the script like this:
.\TestParameters.ps1 `
-AFile "C:\Another\Path" `
-ALetter "B"
which produces output:
Hello World!
(AFile)=(C:\Another\Path)
(ALetter)=(B)
Powershell set the variables $Optional1 and $Optional2 ... but how do I easily display them to the screen, like the way I use $PSBoundParameters?
I do not want to simply write the following every time I have a script:
Write-Host $AFile
Write-Host $ALetter
Write-Host $Optional1
Write-Host $Optional2
Notes:
$args only seems to include unbound parameters, not default
parameters
$MyInvocation seems to only include commands passed on the command lineEDIT: MyInvocation has member variable MyCommand.Parameters, which seems to have all the parameters, not just those passed on the command line...see the accepted answer, below.
Get-Variable seems to include the optional variables in the result list, but I do not know how to differentiate them from the other variables

Answer 1

The following seems to work on my box... probably not the best way to do it, but it seems to work in this case, at least...
[cmdletbinding()]
param([Parameter(Mandatory=$True)]
[string] $AFile = "C:\A\Path",
[Parameter(Mandatory=$True)]
[ValidateSet("A","B","C", "D")]
[string] $ALetter = "A",
[Parameter(Mandatory=$False)]
[ValidateNotNullOrEmpty()]
[string] $Optional1 = "Foo",
[Parameter(Mandatory=$False)]
[ValidateNotNullOrEmpty()]
[string] $Optional2 = "Bar"
)
echo "Hello World!"
($MyInvocation.MyCommand.Parameters ).Keys | %{
$val = (Get-Variable -Name $_ -EA SilentlyContinue).Value
if( $val.length -gt 0 ) {
"($($_)) = ($($val))"
}
}
Saved as allparams.ps1, and run it looks like:
.\allparams.ps1 -ALetter A -AFile "C:\Another\Path"
Hello World!
(AFile) = (C:\Another\Path)
(ALetter) = (A)
(Optional1) = (Foo)
(Optional2) = (Bar)

Answer 2

Using AST:
[CmdletBinding()]
Param (
[Parameter(Mandatory=$True)]
[string] $AFile = "C:\A\Path",
[Parameter(Mandatory=$True)]
[ValidateSet("A","B","C", "D")]
[string] $ALetter = "A",
[Parameter(Mandatory=$False)]
[ValidateNotNullOrEmpty()]
[string] $Optional1 = "Foo",
[Parameter(Mandatory=$False)]
[ValidateNotNullOrEmpty()]
[string] $Optional2 = "Bar"
)
echo "Hello World!"
$psboundparameters.keys | ForEach {
Write-Output "($_)=($($PSBoundParameters.$_))"
}
$ast = [System.Management.Automation.Language.Parser]::
ParseFile($MyInvocation.InvocationName,[ref]$null,[ref]$Null)
$ast.ParamBlock.Parameters | select Name,DefaultValue