How can I know that PowerShell function parameter is omitted

Question

Consider such function:

function Test($foo, $bar)
{
  ...
}

We can call it:

Test -foo $null
Test

How can I know when the -foo was omitted, and when it was $null?

Answer 1

If you are using Powershell V2 or later, you can use the $PSBoundParameters variable which is a dictionary that lists all bound parameters at current scope.

See this blog post that discusses it.