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Editorial Team
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Asked: 2026-05-14T04:02:17+00:00

I don’t know how to execute a command stored as a variable or how

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I don’t know how to execute a command stored as a variable or how to use ifeq inside of a target, so I have a very redundant Makefile at the moment!

Ideally I’d like to have just one target (all) which would run the stored command on Mac and run it twice on Linux, once with -m32 and once with -m64.

all:
    echo PLEASE SELECT OS, e.g. make linux
    exit 1

mac:
     gcc $(SHARED_OPT) $(GENERAL_CFLAGS) $(PLATFORM_CFLAGS) -o $(BUILD_DIR)$(BUILD_NAME) $(SOURCE) $(LIBRARIES)

linux:
    gcc $(SHARED_OPT) $(GENERAL_CFLAGS) $(PLATFORM_CFLAGS) -o $(BUILD_DIR)$(BUILD_NAME64) $(SOURCE) $(LIBRARIES64) -m64
    gcc $(SHARED_OPT) $(GENERAL_CFLAGS) $(PLATFORM_CFLAGS) -o $(BUILD_DIR)$(BUILD_NAME) $(SOURCE) $(LIBRARIES) -m32

UPDATE: This is what I ended up with, after reading the various suggestsions. (Yes I know I should use autoconf . . .) Thanks everyone for your help!

ifeq($(PLATFORM), Linux)
    COMMON = -pthread -fPIC
    PLATFORM_CFLAGS = $(COMMON) -m32
    PLATFORM_CFLAGS64 = $(COMMON) -m64
endif

ifeq ($(PLATFORM), Darwin)
    PLATFORM_CFLAGS = -arch i386 -arch ppc -arch x86_64 -mmacosx-version-min=10.5 -isysroot /Developer/SDKs/MacOSX10.5.sdk
endif

all: $(PLATFORM)_all

Darwin_all:
     mkdir -p ../../../../tmp
     gcc $(SHARED_OPT) $(GENERAL_CFLAGS) $(PLATFORM_CFLAGS) -o $(BUILD_DIR)$(BUILD_NAME) $(SOURCE) $(LIBRARIES)

Linux_all: Darwin_all
     gcc $(SHARED_OPT) $(GENERAL_CFLAGS) $(PLATFORM_CFLAGS64) -o $(BUILD_DIR)$(BUILD_NAME64) $(SOURCE) $(LIBRARIES64)
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1 Answer

  1. Editorial Team

    You make macros do most of the work, noting that you should use $(CC) rather than gcc.

    BUILD_COMMAND = $(CC) $(SHARED_OPT) $(GENERAL_CFLAGS) $(PLATFORM_CFLAGS)
BUILD_NAME32  = $(BUILD_NAME)
TARGET_32     = $(BUILD_DIR)$(BUILD_NAME32)
TARGET_64     = $(BUILD_DIR)$(BUILD_NAME64)
LIBS_32       = $(LIBRARIES)
LIBS_64       = $(LIBRARIES64)
OPTS_32       = -m32
OPTS_64       = -m64

# We could do some fancy stuff here...
# Except that we will remove the commands momentarily
all:
    echo PLEASE SELECT OS, e.g. make linux
    exit 1

# Note that without a qualifier
# - MacOS X 10.5.x will build 32-bit
# - MacOS X 10.6.x will build 64-bit
# But why not build both anyway?
mac:
    $(BUILD_COMMAND) -o $(TARGET_64) $(SOURCE) $(LIBS_64) $(OPTS_64)
    $(BUILD_COMMAND) -o $(TARGET_32) $(SOURCE) $(LIBS_32) $(OPTS_32)

linux:
    $(BUILD_COMMAND) -o $(TARGET_64) $(SOURCE) $(LIBS_64) $(OPTS_64)
    $(BUILD_COMMAND) -o $(TARGET_32) $(SOURCE) $(LIBS_32) $(OPTS_32)

    Oh, and look, the commands are the same for Linux and MacOS X now…so we can do:

    BUILD_COMMAND = $(CC) $(SHARED_OPT) $(GENERAL_CFLAGS) $(PLATFORM_CFLAGS)
BUILD_NAME32  = $(BUILD_NAME)
TARGET_32     = $(BUILD_DIR)$(BUILD_NAME32)
TARGET_64     = $(BUILD_DIR)$(BUILD_NAME64)
LIBS_32       = $(LIBRARIES)
LIBS_64       = $(LIBRARIES64)
OPTS_32       = -m32
OPTS_64       = -m64

all:
    $(BUILD_COMMAND) -o $(TARGET_64) $(SOURCE) $(LIBS_64) $(OPTS_64)
    $(BUILD_COMMAND) -o $(TARGET_32) $(SOURCE) $(LIBS_32) $(OPTS_32)

    Gosh, it is hard work writing $(XXX) instead of ${XXX} as I normally do in my makefiles.

    Basically, we apply DRY (Don’t Repeat Yourself) by making names boringly systematic. Makefiles should not be exciting.

    If you still want to have a difference between your platforms, then you can do something along the lines suggested by Ivan Andrus. GNU Make allows you to evaluate shell commands, so:

    BUILD_COMMAND = $(CC) $(SHARED_OPT) $(GENERAL_CFLAGS) $(PLATFORM_CFLAGS)
BUILD_NAME32  = $(BUILD_NAME)
TARGET_32     = $(BUILD_DIR)$(BUILD_NAME32)
TARGET_64     = $(BUILD_DIR)$(BUILD_NAME64)
LIBS_32       = $(LIBRARIES)
LIBS_64       = $(LIBRARIES64)
OPTS_32       = -m32
OPTS_64       = -m64

all:  $(shell uname)

Linux:
    $(BUILD_COMMAND) -o $(TARGET_64) $(SOURCE) $(LIBS_64) $(OPTS_64)
    $(BUILD_COMMAND) -o $(TARGET_32) $(SOURCE) $(LIBS_32) $(OPTS_32)

Darwin:
    $(BUILD_COMMAND) -o $(TARGET_32) $(SOURCE) $(LIBS_32)

    If you feel you can’t rely on GNU Make, then:

    BUILD_COMMAND = $(CC) $(SHARED_OPT) $(GENERAL_CFLAGS) $(PLATFORM_CFLAGS)
BUILD_NAME32  = $(BUILD_NAME)
TARGET_32     = $(BUILD_DIR)$(BUILD_NAME32)
TARGET_64     = $(BUILD_DIR)$(BUILD_NAME64)
LIBS_32       = $(LIBRARIES)
LIBS_64       = $(LIBRARIES64)
OPTS_32       = -m32
OPTS_64       = -m64
BUILD_32      = use_32_bit
BUILD_64      = use_64_bit
BUILD_TYPE    = $(BUILD_32) $(BUILD_64)

.PHONEY: $(BUILD_32) $(BUILD_64)

all:  $(BUILD_TYPE)

use_64_bit:
    $(BUILD_COMMAND) -o $(TARGET_64) $(SOURCE) $(LIBS_64) $(OPTS_64)

use_32_bit:
    $(BUILD_COMMAND) -o $(TARGET_32) $(SOURCE) $(LIBS_32) $(OPTS_32)

    By default this will compile both 32-bit and 64-bit versions.
    If you want 32-bit only or 64-bit only, run the appropriate one of these two:

    make BUILD_TYPE=use_32_bit
make BUILD_TYPE=use_64_bit
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