Make: Environment Variables

Cited from Variables from the Environment

"Variables in make can come from the environment in which make is run. Every environment variable that make sees when it starts up is transformed into a make variable with the same name and value. However, an explicit assignment in the makefile, or with a command argument, overrides the environment. (If the ‘-e’ flag is specified, then values from the environment override assignments in the makefile. See Summary of Options. But this is not recommended practice.)"

=======================================
Cited from The Basics: Getting environment variables into GNU Make

"The override directive beats the command line which beats environment overrides (-e option) which beats macros defined in a Makefile file which beats the original environment."