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

Question

I have a shell script that is used both on Windows/Cygwin and Mac and Linux. It needs slightly different variables for each versions. How can a shell/bash script detect whether it is running in Cygwin, on a Mac or in Linux?

Accepted Answer

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;;
    MSYS_NT*)   machine=Git;;
    *)          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`).

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

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