OS detecting makefile
I routinely work on several different computers and several different operating systems, which are Mac OS X, Linux, or Solaris. For the project I'm working on, I pull my code from a remote git repository.
I like to be able to work on my projects regardless of which terminal I'm at. So far, I've found ways to get around the OS changes by changing the makefile every time I switch computers. However, this is tedious and causes a bunch of headaches.
How can I modify my makefile so that it detects which OS I'm using and modifies syntax accordingly?
Here is the makefile:
cc = gcc -g
CC = g++ -g
yacc=$(YACC)
lex=$(FLEX)
all: assembler
assembler: y.tab.o lex.yy.o
$(CC) -o assembler y.tab.o lex.yy.o -ll -l y
assembler.o: assembler.c
$(cc) -o assembler.o assembler.c
y.tab.o: assem.y
$(yacc) -d assem.y
$(CC) -c y.tab.c
lex.yy.o: assem.l
$(lex) assem.l
$(cc) -c lex.yy.c
clean:
rm -f lex.yy.c y.tab.c y.tab.h assembler *.o *.tmp *.debug *.acts
There are many good answers here already, but I wanted to share a more complete example that both:
uname exists on Windows The CCFLAGS defined here aren't necessarily recommended or ideal; they're just what the project to which I was adding OS/CPU auto-detection happened to be using.
ifeq ($(OS),Windows_NT)
CCFLAGS += -D WIN32
ifeq ($(PROCESSOR_ARCHITEW6432),AMD64)
CCFLAGS += -D AMD64
else
ifeq ($(PROCESSOR_ARCHITECTURE),AMD64)
CCFLAGS += -D AMD64
endif
ifeq ($(PROCESSOR_ARCHITECTURE),x86)
CCFLAGS += -D IA32
endif
endif
else
UNAME_S := $(shell uname -s)
ifeq ($(UNAME_S),Linux)
CCFLAGS += -D LINUX
endif
ifeq ($(UNAME_S),Darwin)
CCFLAGS += -D OSX
endif
UNAME_P := $(shell uname -p)
ifeq ($(UNAME_P),x86_64)
CCFLAGS += -D AMD64
endif
ifneq ($(filter %86,$(UNAME_P)),)
CCFLAGS += -D IA32
endif
ifneq ($(filter arm%,$(UNAME_P)),)
CCFLAGS += -D ARM
endif
endif
The uname command (http://developer.apple.com/documentation/Darwin/Reference/ManPages/man1/uname.1.html) with no parameters should tell you the operating system name. I'd use that, then make conditionals based on the return value.
Example
UNAME := $(shell uname)
ifeq ($(UNAME), Linux)
# do something Linux-y
endif
ifeq ($(UNAME), Solaris)
# do something Solaris-y
endif
If you do not need sophisticated stuff as done by Git LFS, you can detect the Operating System just using two simple tricks:
OS uname -s ifeq ($(OS),Windows_NT)
detected_OS := Windows
else
detected_OS := $(shell uname -s)
endif
Or a more safe way, if not Windows and command uname not available:
ifeq ($(OS),Windows_NT)
detected_OS := Windows
else
detected_OS := $(shell sh -c 'uname -s 2>/dev/null || echo not')
endif
Then you can select the relevant stuff depending on detected_OS :
ifeq ($(detected_OS),Windows)
CFLAGS += -D WIN32
endif
ifeq ($(detected_OS),Darwin) # Mac OS X
CFLAGS += -D OSX
endif
ifeq ($(detected_OS),Linux)
CFLAGS += -D LINUX
endif
ifeq ($(detected_OS),GNU) # Debian GNU Hurd
CFLAGS += -D GNU_HURD
endif
ifeq ($(detected_OS),GNU/kFreeBSD) # Debian kFreeBSD
CFLAGS += -D GNU_kFreeBSD
endif
ifeq ($(detected_OS),FreeBSD)
CFLAGS += -D FreeBSD
endif
ifeq ($(detected_OS),NetBSD)
CFLAGS += -D NetBSD
endif
ifeq ($(detected_OS),DragonFly)
CFLAGS += -D DragonFly
endif
ifeq ($(detected_OS),Haiku)
CFLAGS += -D Haiku
endif
Please see also this detailed answer about importance of uname -s better than uname -o .
The use of OS (instead of uname -s ) simplifies the identification algorithm. You can still use solely uname -s but you have to deal with if/else blocks to check all MinGW/Cygwin/... variations.
Note: The environment variable OS is always set to "Windows_NT" on any Windows platform (see Windows Environment Variables on Wikipedia). An alternative of OS is the environment variable MSVC (it checks the presence of MS Visual Studio, see example using MSVC).
Below I provide a complete example using make and gcc to build a shared library: *.so or *.dll depending on the platform. The example is as simplest as possible to be more understandable :-)
To install make and gcc on Windows see Cygwin or MinGW.
My example is based on 5 files
├── lib
│ └── Makefile
│ └── hello.h
│ └── hello.c
└── app
└── Makefile
└── main.c
Do not forget: files Makefile are indented using tabulations.
The two files Makefile
1. lib/Makefile
ifeq ($(OS),Windows_NT)
uname_S := Windows
else
uname_S := $(shell uname -s)
endif
ifeq ($(uname_S), Windows)
target = hello.dll
endif
ifeq ($(uname_S), Linux)
target = libhello.so
endif
#ifeq ($(uname_S), .....) #See https://stackoverflow.com/a/27776822/938111
# target = .....
#endif
%.o: %.c
gcc -c $< -fPIC -o $@
# -c $< => $< is first file after ':' => Compile hello.c
# -fPIC => Position-Independent Code (required for shared lib)
# -o $@ => $@ is the target => Output file (-o) is hello.o
$(target): hello.o
gcc $^ -shared -o $@
# $^ => $^ expand to all prerequisites (after ':') => hello.o
# -shared => Generate shared library
# -o $@ => Output file (-o) is $@ (libhello.so or hello.dll)
2. app/Makefile
ifeq ($(OS),Windows_NT)
uname_S := Windows
else
uname_S := $(shell uname -s)
endif
ifeq ($(uname_S), Windows)
target = app.exe
endif
ifeq ($(uname_S), Linux)
target = app
endif
#ifeq ($(uname_S), .....) #See https://stackoverflow.com/a/27776822/938111
# target = .....
#endif
%.o: %.c
gcc -c $< -I ../lib -o $@
# -c $< => compile (-c) $< (first file after :) = main.c
# -I ../lib => search headers (*.h) in directory ../lib
# -o $@ => output file (-o) is $@ (target) = main.o
$(target): main.o
gcc $^ -L../lib -lhello -o $@
# $^ => $^ (all files after the :) = main.o (here only one file)
# -L../lib => look for libraries in directory ../lib
# -lhello => use shared library hello (libhello.so or hello.dll)
# -o $@ => output file (-o) is $@ (target) = "app.exe" or "app"
To learn more, read Automatic Variables documentation as pointed out by cfi.
The source code
- lib/hello.h
#ifndef HELLO_H_
#define HELLO_H_
const char* hello();
#endif
- lib/hello.c
#include "hello.h"
const char* hello()
{
return "hello";
}
- app/main.c
#include "hello.h" //hello()
#include <stdio.h> //puts()
int main()
{
const char* str = hello();
puts(str);
}
The build
Fix the copy-paste of Makefile (replace leading spaces by one tabulation).
> sed 's/^ */t/' -i */Makefile
The make command is the same on both platforms. The given output is on Unix-like OSes:
> make -C lib
make: Entering directory '/tmp/lib'
gcc -c hello.c -fPIC -o hello.o
# -c hello.c => hello.c is first file after ':' => Compile hello.c
# -fPIC => Position-Independent Code (required for shared lib)
# -o hello.o => hello.o is the target => Output file (-o) is hello.o
gcc hello.o -shared -o libhello.so
# hello.o => hello.o is the first after ':' => Link hello.o
# -shared => Generate shared library
# -o libhello.so => Output file (-o) is libhello.so (libhello.so or hello.dll)
make: Leaving directory '/tmp/lib'
> make -C app
make: Entering directory '/tmp/app'
gcc -c main.c -I ../lib -o main.o
# -c main.c => compile (-c) main.c (first file after :) = main.cpp
# -I ../lib => search headers (*.h) in directory ../lib
# -o main.o => output file (-o) is main.o (target) = main.o
gcc main.o -L../lib -lhello -o app
# main.o => main.o (all files after the :) = main.o (here only one file)
# -L../lib => look for libraries in directory ../lib
# -lhello => use shared library hello (libhello.so or hello.dll)
# -o app => output file (-o) is app.exe (target) = "app.exe" or "app"
make: Leaving directory '/tmp/app'
The run
The application requires to know where is the shared library.
On Windows, a simple solution is to copy the library where the application is:
> cp -v lib/hello.dll app
`lib/hello.dll' -> `app/hello.dll'
On Unix-like OSes, you can use the LD_LIBRARY_PATH environment variable:
> export LD_LIBRARY_PATH=lib
Run the command on Windows:
> app/app.exe
hello
Run the command on Unix-like OSes:
> app/app
hello
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