I ran into the same issue as @kamadoatfluid in #832, as I have a mounted disk path including a $ (valid file & folder character in most operating systems, as is %). Since this is intended to catch environment variables per #662, I propose the use of regex instead to prevent irrelevant warnings from cluttering logs/console output.

This PR supports all expansion conventions demonstrated in os.path.expandvars, and also aligns with environment variable naming specifications. Illegal variables simply will cause errors and therefore don't present a security risk: word characters only, beginning with a-z or _.

Supported formats:

• % APPDATA % or %APPDATA%
• $MYVAR
• ${MYVAR}