OS detecting makefile

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

The git makefile contains numerous examples of how to manage without autoconf/automake, yet still work on a multitude of unixy platforms.

That's the job that GNU's automake/autoconf are designed to solve. You might want to investigate them.

Alternatively you can set environment variables on your different platforms and make you Makefile conditional against them.

I finally found the perfect solution that solves this problem for me.

ifeq '$(findstring ;,$(PATH))' ';'
    UNAME := Windows
else
    UNAME := $(shell uname 2>/dev/null || echo Unknown)
    UNAME := $(patsubst CYGWIN%,Cygwin,$(UNAME))
    UNAME := $(patsubst MSYS%,MSYS,$(UNAME))
    UNAME := $(patsubst MINGW%,MSYS,$(UNAME))
endif

The UNAME variable is set to Linux, Cygwin, MSYS, Windows, FreeBSD, NetBSD (or presumably Solaris, Darwin, OpenBSD, AIX, HP-UX), or Unknown. It can then be compared throughout the remainder of the Makefile to separate any OS-sensitive variables and commands.

The key is that Windows uses semicolons to separate paths in the PATH variable whereas everyone else uses colons. (It's possible to make a Linux directory with a ';' in the name and add it to PATH, which would break this, but who would do such a thing?) This seems to be the least risky method to detect native Windows because it doesn't need a shell call. The Cygwin and MSYS PATH use colons so uname is called for them.

Note that the OS environment variable can be used to detect Windows, but not to distinguish between Cygwin and native Windows. Testing for the echoing of quotes works, but it requires a shell call.

Unfortunately, Cygwin adds some version information to the output of uname, so I added the 'patsubst' calls to change it to just 'Cygwin'. Also, uname for MSYS actually has three possible outputs starting with MSYS or MINGW, but I use also patsubst to transform all to just 'MSYS'.

If it's important to distinguish between native Windows systems with and without some uname.exe on the path, this line can be used instead of the simple assignment:

UNAME := $(shell uname 2>NUL || echo Windows)

Of course in all cases GNU make is required, or another make which supports the functions used.

I had a case where I had to detect the difference between two versions of Fedora, to tweak the command-line options for inkscape:
- in Fedora 31, the default inkscape is 1.0beta which uses --export-file
- in Fedora < 31, the default inkscape is 0.92 which uses --export-pdf

My Makefile contains the following

# set VERSION_ID from /etc/os-release

$(eval $(shell grep VERSION_ID /etc/os-release))

# select the inkscape export syntax

ifeq ($(VERSION_ID),31)
EXPORT = export-file
else
EXPORT = export-pdf
endif

# rule to convert inkscape SVG (drawing) to PDF

%.pdf : %.svg
    inkscape --export-area-drawing $< --$(EXPORT)=$@

This works because /etc/os-release contains a line

VERSION_ID=<value>

so the shell command in the Makefile returns the string VERSION_ID=<value>, then the eval command acts on this to set the Makefile variable VERSION_ID. This can obviously be tweaked for other OS's depending how the metadata is stored. Note that in Fedora there is not a default environment variable that gives the OS version, otherwise I would have used that!

An alternate way that I have not seen anyone talking about is using the built-in variable SHELL. The program used as the shell is taken from the variable SHELL. On MS-Windows systems, it is most likely to be an executable file with .exe extension (like sh.exe).

In that case, the following conditional test:

ifeq ($(suffix $(SHELL)),.exe)
    # Windows system
else
    # Non-Windows system
endif

Would have the same result as using the environment variable OS:

ifeq ($(OS),Windows_NT)
    # Windows system
else
    # Non-Windows system
endif

However, it seems the latter is the most popular solution, so I would recommend you stick with it.