get a default value when variable is unset in make

Question

(edit: question more accurate based on @Michael feedback)

In bash, I often use parameter expansion: the following commands print \"default value\" when

Answer 1

I have a similar case where the result of filtering a shell command could be a single word or empty string. When empty, it should fallback to the default word. In the example below APPLE_LINUX will be 'apple' on macOS or 'linux' on other platforms. MSG will be set to the message for the appropriate platform. The example intentionality avoids using ifeq.

MACHINE         := $(shell $(COMPILE.cpp) -dumpmachine)
MACHINE_APPLE   := $(findstring apple,$(MACHINE))
APPLE_LINUX     := $(firstword $(MACHINE_APPLE) linux)
apple.MSG       := You are building on macOS
linux.MSG       := You are building on Linux or another OS
MSG             := $($(APPLE_LINUX).MSG)