Get operating system as string identifier from $OSTYPE

ostype.sh

#!/bin/sh

#
# get os type
#

get_os() {
  if [ -z $OSTYPE ]; then
    OSTYPE=$(uname | tr '[:upper:]' '[:lower:]')
  fi

  case $OSTYPE in
    freebsd*) echo "freebsd" ;;
    netbsd*) echo "netbsd" ;;
    openbsd*) echo "openbsd" ;;
    darwin*) echo "mac" ;;
    linux*) echo "linux" ;;
    cygwin*) echo "cygwin" ;;
    *) echo "unknown"; exit 1 ;;
  esac
}

edit: add OSTYPE fallback for non-posix shells.

edit: add bsd types.

This will fail when OSTYPE is set to something that isn't all lowercase (FreeBSD).