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 de

Answer 1

To build upon Albert's answer, I like to use $COMSPEC for detecting Windows:

#!/bin/bash

if [ "$(uname)" == "Darwin" ]
then
 echo Do something under Mac OS X platform
elif [ "$(expr substr $(uname -s) 1 5)" == "Linux" ]
then
  echo Do something under Linux platform
elif [ -n "$COMSPEC" -a -x "$COMSPEC" ]
then 
  echo $0: this script does not support Windows \:\(
fi

This avoids parsing variants of Windows names for $OS, and parsing variants of uname like MINGW, Cygwin, etc.

Background: %COMSPEC% is a Windows environmental variable specifying the full path to the command processor (aka the Windows shell). The value of this variable is typically %SystemRoot%\system32\cmd.exe, which typically evaluates to C:\Windows\system32\cmd.exe .