Makefile ifeq with Bash commands on OS X

Question

I am trying to write a Makefile that evaluates results from Bash commands, e.g., uname.

Makefile:

OS1 = $(uname)
OS2 = Darwin

all:
    @echo $(value OS1)

ifeq ($(uname),Darwin)
    @echo "OK"
else
    @echo "Fail"
endif

ifeq ($(OS1),Darwin)
    @echo "OK"
else
    @echo "Fail"
endif

ifeq ($(OS2),Darwin)
    @echo "OK"
else
    @echo "Fail"
endif

Output:

Darwin
Fail
Fail
OK

How can I compare the variable OS1 or the command $(uname) to the literal Darwin inside an ifeq? From what I have read, the second ifeq in my Makefile should work, but it doesn't.

I am using GNU Make 3.81 for i386-apple-darwin11.3.0 on OS X 10.9.3.

Answer 1

There are a lot of different questions and answers about Makefiles, variables and shell commands. But as it turns out, looking into the manual is sometimes more reliable than searching Stackoverflow.

First, I didn't know the different ways that variables can be assigned in GNU make: https://www.gnu.org/software/make/manual/make.html#Reading-Makefiles

Second, the shell function, which is required in this case, only works in combination with the := (immediate) operator: https://www.gnu.org/software/make/manual/make.html#Shell-Function

Thus the correct Makefile looks like this:

OS := $(shell uname)

all:
    @echo $(OS)

ifeq ($(shell uname),Darwin)
    @echo "OK"
else
    @echo "Fail"
endif

ifeq ($(OS),Darwin)
    @echo "OK"
else
    @echo "Fail"
endif