detect os in bash

detect-os.sh

#!/usr/bin/env bash

# "unofficial" bash strict mode
# See: http://redsymbol.net/articles/unofficial-bash-strict-mode
set -o errexit  # Exit when simple command fails               'set -e'
set -o errtrace # Exit on error inside any functions or subshells.
set -o nounset  # Trigger error when expanding unset variables 'set -u'
set -o pipefail # Do not hide errors within pipes              'set -o pipefail'
IFS=$'\n\t'

# do nothing if the library is already sourced in the same shell
((${__sourced__-})) && return
( return 0 2>/dev/null) && __sourced__=1 || __sourced__=0

os_name() {
  UNAME=$( command -v uname)
  TR=$( command -v tr)
  
  case $( "${UNAME}" | "${TR}" '[:upper:]' '[:lower:]') in
    linux*)	              printf 'linux\n'  ;;
    darwin*)              printf 'osx\n' ;;
    nt|win*)              printf 'windows\n' ;;
    msys*|cygwin*|mingw*) printf 'windows\n' ;;   # or possibly 'bash on windows'
    *)                    printf 'unknown\n' ;;
  esac
  unset -v UNAME
  true
}

if ((${__sourced__-})); then
  export -f os_name
else
  os_name
  return $? 2>/dev/null || exit $?
 fi