How to check if running in Cygwin, Mac or Linux?

Detect three different OS types (GNU/Linux, Mac OS X, Windows NT)

Notes

• 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 bash

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

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

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

pax> uname -a
CYGWIN_NT-5.1 IBM-L3F3936 1.5.25(0.156/4/2) 2008-06-12 19:34 i686 Cygwin

pax> uname -s
CYGWIN_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}"
esac
echo ${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).