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makefilegnu-make

What is $(OS) in a Makefile conditional?

Coming from https://gist.github.com/sighingnow/deee806603ec9274fd47#file-makefile-L6, the below works:

ifeq ($(OS), Windows_NT)
    IS_WINDOWS = 1
else
    IS_WINDOWS = 0
endif

This $(OS) in a conditional, I can't find docs on it anywhere. What is the story with $(OS), and can anyone provide docs on this?

Solution

  • The OS environment variable is available on Windows systems; see e.g. this list of Windows environment variables.

    This conditional...

    ifeq ($(OS), Windows_NT)

    ...is checking if make is running on Windows by looking at the value of the OS environment variable. If it is equal to Windows_NT, make sets IS_WINDOWS=1.

    Otherwise, make sets IS_WINDOWS=0.