makefile ifeq ($(LANG),) 判断操作系统

ifeq ($(LANG),)

# Customize for Windows
# The MIPS gcc compiler must use the cygwin1.dll that came with the compiler.
CC_X86 = cl /O1 /nologo
CP = copy
RM = del
DWIN32 = -DWIN32
BIN_MIPS = ..\gccmips_elf
VHDL_DIR = ..\vhdl
LINUX_PWD =
GCC_MIPS  = $(BIN_MIPS)\gcc $(CFLAGS)
AS_MIPS   = $(BIN_MIPS)\as
LD_MIPS   = $(BIN_MIPS)\ld
DUMP_MIPS = $(BIN_MIPS)\objdump
CONVERT_BIN = $(LINUX_PWD)convert_bin.exe

else

# Customized for Linux
# See http://www.opencores.com/projects.cgi/web/mips/linux_tools.htm
CC_X86 = gcc -Wall -O -g
CP = cp
RM = rm -rf 
DWIN32 =
BIN_MIPS = 
VHDL_DIR = ../vhdl
LINUX_PWD = ./
#GCC_MIPS  = $(BIN_MIPS)mips-elf-gcc $(CFLAGS)
#AS_MIPS   = $(BIN_MIPS)mips-elf-as
#LD_MIPS   = $(BIN_MIPS)mips-elf-ld
#DUMP_MIPS = $(BIN_MIPS)mips-elf-objdump
GCC_MIPS = mips-uclibc-gcc $(CFLAGS)
AS_MIPS = mips-uclibc-as
LD_MIPS = mips-uclibc-ld
DUMP_MIPS = mips-uclibc-objdump
CONVERT_BIN = $(LINUX_PWD)convert_bin.exe
#CONVERT_BIN = $(BIN_MIPS)mips-elf-objcopy -I elf32-big -O binary test.axf test.bin

endif

一般情况下，linux是有 LANG这个环境变量 而window没有的，所有通过  ifeq ($(LANG),)  是否为空即可判断操作系统。

windows情况下，一般情况是要用cl.exe 编译的，所以要用if 之下 else之上的块。

但是，不一般的情况，比如装个matlab，系统会增加环境变量Lang ，于是， gmake all出错了。

判断方法  echo %LANG%   解决方案： set LANG=  (只在当前cmd窗口有效)