Parse the contents of a string on-the-fly in PowerShell [duplicate]

Question

The first example below is a normal static string getting parsed. The second example is me attempting to do the same thing but get the string to parse live, dynamically. I need to know what to put in the place of (($myparse gets evaluated)) below in order to get it to parse the contents of $myparse on-the-fly. I'm sure it's some kind of script block, but I can't figure out what kind.

The following code correctly parses the static string as "Hello John Smith" and stores it in $mysalutation:

>$firstName = "John"
>$lastName = "Smith"
>$mysalutation = "Hello $firstName$(if($lastname) {" " + $lastName})."
>$mysalutation
Hello John Smith.

What I want to do is parse the same string on the fly:

>$myparse = 'Hello $firstName$(if($lastname) {" " + $lastName}).'
>$myparse
Hello $firstName$(if($lastname) {" " + $lastName}).

>$firstName = "Jason"
>$lastName = "Bourne"
>$mysalutation = (($myparse gets evaluated))
>$mysalutation
Hello Jason Bourne.

Answer 1

You are looking for the ExpandString function:

$ExecutionContext.InvokeCommand.ExpandString($myparse)