I think the following should work. I’m not sure about win32
though.
if [[ "$OSTYPE" == "linux-gnu"* ]]; then
# ...
elif [[ "$OSTYPE" == "darwin"* ]]; then
# Mac OSX
elif [[ "$OSTYPE" == "cygwin" ]]; then
# POSIX compatibility layer and Linux environment emulation for Windows
elif [[ "$OSTYPE" == "msys" ]]; then
# Lightweight shell and GNU utilities compiled for Windows (part of MinGW)
elif [[ "$OSTYPE" == "win32" ]]; then
# I'm not sure this can happen.
elif [[ "$OSTYPE" == "freebsd"* ]]; then
# ...
else
# Unknown.
fi