What does ${$} mean / do in PowerShell?
The input ${$} gets evaluated as the automatic variable $$. $$ itself is set to the last token of the last input line in the session. In your case it is set to the last argument home\env.txt
You can see this effect also with input like ${?} that results in $?, another automatic variable, which contains the result of the last executed command.
For a list of automatic variables see: https://docs.microsoft.com/en-us/powershell/module/microsoft.powershell.core/about/about_automatic_variables