Usually, uname with its various options will tell you what environment you're running in:

pax> uname -aCYGWIN_NT-5.1 IBM-L3F3936 1.5.25(0.156/4/2) 2008-06-12 19:34 i686 Cygwinpax> uname -sCYGWIN_NT-5.1

And, according to the very helpful schot (in the comments), uname -s gives Darwin for OSX and Linux for Linux, while my Cygwin gives CYGWIN_NT-5.1. But you may have to experiment with all sorts of different versions.

So the bash code to do such a check would be along the lines of:

unameOut="$(uname -s)"case "${unameOut}" in    Linux*)     machine=Linux;;    Darwin*)    machine=Mac;;    CYGWIN*)    machine=Cygwin;;    MINGW*)     machine=MinGw;;    *)          machine="UNKNOWN:${unameOut}"esacecho ${machine}

Note that I'm assuming here that you're actually running within CygWin (the bash shell of it) so paths should already be correctly set up. As one commenter notes, you can run the bash program, passing the script, from cmd itself and this may result in the paths not being set up as needed.

If you are doing that, it's your responsibility to ensure the correct executables (i.e., the CygWin ones) are being called, possibly by modifying the path beforehand or fully specifying the executable locations (e.g., /c/cygwin/bin/uname).

Here is the bash script I used to detect three different OS type (GNU/Linux, Mac OS X, Windows NT)

Pay attention

• In your bash script, use #!/usr/bin/env bash instead of #!/bin/sh to prevent the problem caused by /bin/sh linked to different default shell in different platforms, or there will be error like unexpected operator, that's what happened on my computer (Ubuntu 64 bits 12.04).
• Mac OS X 10.6.8 (Snow Leopard) do not have expr program unless you install it, so I just use uname.

Design

1. Use uname to get the system information (-s parameter).
2. Use expr and substr to deal with the string.
3. Use if elif fi to do the matching job.
4. You can add more system support if you want, just follow the uname -s specification.

Implementation

#!/usr/bin/env bashif [ "$(uname)" == "Darwin" ]; then    # Do something under Mac OS X platform        elif [ "$(expr substr $(uname -s) 1 5)" == "Linux" ]; then    # Do something under GNU/Linux platformelif [ "$(expr substr $(uname -s) 1 10)" == "MINGW32_NT" ]; then    # Do something under 32 bits Windows NT platformelif [ "$(expr substr $(uname -s) 1 10)" == "MINGW64_NT" ]; then    # Do something under 64 bits Windows NT platformfi

Testing

• Linux (Ubuntu 12.04 LTS, Kernel 3.2.0) tested OK.
• OS X (10.6.8 Snow Leopard) tested OK.
• Windows (Windows 7 64 bit) tested OK.

What I learned

1. Check for both opening and closing quotes.
2. Check for missing parentheses and braces {}

References

• [1] uname - wikipedia
• [2] shell script syntax error: unexpected end of file
• [3] Detect the OS from a Bash script
• [4] BASH Programming Introduction HOW-TO

Use uname -s (--kernel-name) because uname -o (--operating-system) is not supported on some Operating Systems such as Mac OS and Solaris. You may also use just uname without any argument since the default argument is -s (--kernel-name).

The below snippet does not require bash (i.e. does not require #!/bin/bash)

#!/bin/shcase "$(uname -s)" in   Darwin)     echo 'Mac OS X'     ;;   Linux)     echo 'Linux'     ;;   CYGWIN*|MINGW32*|MSYS*|MINGW*)     echo 'MS Windows'     ;;   # Add here more strings to compare   # See correspondence table at the bottom of this answer   *)     echo 'Other OS'      ;;esac

The below Makefile is inspired from Git project (config.mak.uname).

ifdef MSVC     # Avoid the MingW/Cygwin sections    uname_S := Windowselse                          # If uname not available => 'not'     uname_S := $(shell sh -c 'uname -s 2>/dev/null || echo not')endif# Avoid nesting "if .. else if .. else .. endif endif"# because maintenance of matching if/else/endif is a painifeq ($(uname_S),Windows)    CC := cl endififeq ($(uname_S),OSF1)    CFLAGS += -D_OSF_SOURCEendififeq ($(uname_S),Linux)    CFLAGS += -DNDEBUGendififeq ($(uname_S),GNU/kFreeBSD)    CFLAGS += -D_BSD_ALLOCendififeq ($(uname_S),UnixWare)    CFLAGS += -Wextraendif...

See also this complete answer about uname -s and Makefile.

The correspondence table in the bottom of this answer is from Wikipedia article about uname. Please contribute to keep it up-to-date (edit the answer or post a comment). You may also update the Wikipedia article and post a comment to notify me about your contribution ;-)

Operating System uname -s
Mac OS X Darwin
Cygwin 32-bit (Win-XP) CYGWIN_NT-5.1
Cygwin 32-bit (Win-7 32-bit)CYGWIN_NT-6.1
Cygwin 32-bit (Win-7 64-bit)CYGWIN_NT-6.1-WOW64
Cygwin 64-bit (Win-7 64-bit)CYGWIN_NT-6.1
MinGW (Windows 7 32-bit) MINGW32_NT-6.1
MinGW (Windows 10 64-bit) MINGW64_NT-10.0
Interix (Services for UNIX) Interix
MSYS MSYS_NT-6.1
MSYS2 MSYS_NT-10.0-17763
Windows Subsystem for Linux Linux
Android Linux
coreutils Linux
CentOS Linux
Fedora Linux
Gentoo Linux
Red Hat Linux Linux
Linux Mint Linux
openSUSE Linux
Ubuntu Linux
Unity Linux Linux
Manjaro Linux Linux
OpenWRT r40420 Linux
Debian (Linux) Linux
Debian (GNU Hurd) GNU
Debian (kFreeBSD) GNU/kFreeBSD
FreeBSD FreeBSD
NetBSD NetBSD
OpenBSD OpenBSD
DragonFlyBSD DragonFly
Haiku Haiku
NonStop NONSTOP_KERNEL
QNX QNX
ReliantUNIX ReliantUNIX-Y
SINIX SINIX-Y
Tru64 OSF1
Ultrix ULTRIX
IRIX 32 bits IRIX
IRIX 64 bits IRIX64
MINIX Minix
Solaris SunOS
UWIN (64-bit Windows 7) UWIN-W7
SYS$UNIX:SH on OpenVMS IS/WB
z/OS USS OS/390
Cray sn5176
(SCO) OpenServer SCO_SV
(SCO) System V SCO_SV
(SCO) UnixWare UnixWare
IBM AIX AIX
IBM i with QSH OS400
HP-UX HP-UX