Powershell: Force variable expansion - powershell

Question

How can I force string variable expansion?
I need to read a string with one or more variable names in it (a template) and then expand it after I read the file. The key is that I must read the contents of the file before I declare the variables that will be used in the expansion. I've tried several ways but I can't get it to work.
It's not an option to read the file after $environment is defined.
Contents of name.txt:
$environment-RPT-INT
#example 1
$name = gc "c:\temp\name.txt"
$environment = "9065DEV"
$expanded = $ExecutionContext.InvokeCommand.ExpandString($name)
$expanded
#example 2
$name = gc "c:\temp\name.txt"
$environment = "9065DEV"
$expanded = $expanded = Invoke-Expression "`"$template`""
$expanded
#example 3
$name = gc "c:\temp\name.txt"
$environment = "9065DEV"
$name = $name.Clone()
$expanded = $ExecutionContext.InvokeCommand.ExpandString($name)
$expanded
Any help is appreciated.
Updated: Example 1 is now working for me.

Answer 1

It looks like you've found some possible solutions, but I'll suggest another that is in my opinion a bit smarter and more robust.
Instead of requiring variable names in your text file, why not use format specifiers. For example, the contents of name.txt:
{0}-RPT-INT
And in your script:
$name = gc "c:\temp\name.txt"
$environment = "9065DEV"
$expanded = $name -f $environment
$expanded
This way, you can rename the variable w/o changing any of your text files. As a bonus, if your text file comes from unknown sources, your script is vulnerable to code injection. For example, say you are given a text file with these contents:
$(rm -whatif -recurse -force c:\)-RPT-INT
Then ExpandString or Invoke-Expression will happily execute that code.

Answer 2

Your Invoke-Expression example is pretty close. Instead of using $template though, you need to use $name.
#example 2
$name = gc 'c:\temp\name.txt';
$environment = '9065DEV';
$expanded = Invoke-Expression -Command "`"$name`"";
$expanded;

Answer 3

If you are willing to store your Setting/Values in a CSV, I wrote a module to pull values from a CSV, put it into a HereString... any variables you put into the CSV become fully expanded inside the Here-String. That way, you can normally address the field names and values.
I might be able to change this to also work with traditional INI's if anyone is interested.
https://github.com/Inventologist?tab=repositories
Look for: HereStringFromCSV

Answer 4

There is a function called ExpandString predefined in powershell. It's inside $ExecutionContext, as follows.
$mystring = #'
This is a here string with some embedded variables.
Here is variable foo -- $foo
Here is variable bar -- $bar
Here is variable bletch -- $bletch
'#
#This displays the here string as is.
$mystring
#now define foo, bar and bletch
$foo = 5
$bar = Get-Date
$bletch = "George Washington"
#now run the here string through Expandstring.
$ExecutionContext.InvokeCommand.ExpandString($mystring)