All the Windows environment variables are read by Vim and they are available in Vim as Vim environment variables. Vim environment variables begin with the character
$. Hence, the Windows environment variable name is prefixed with the
$ character when it becomes a Vim environment variable.
For example, the Windows environment variable
%USERPROFILE% will be available as
$USERPROFILE inside Vim.
This post shows how you can list all the environment variables or view the value of a particular variable.