osdetect

#!/usr/bin/env bash
set -o nounset
set -o errexit
set -o errtrace
set -o pipefail
IFS=$'\n\t'

###############################################################################
# Environment
###############################################################################

# $_ME
#
# This program's basename.
_ME="$(basename "${0}")"

###############################################################################
# Help
###############################################################################

# _print_help()
#
# Usage:
#   _print_help
#
# Description:
#   Print the program help information.
_print_help() {
  cat <<HEREDOC
Usage:
  ${_ME}
  ${_ME} -h | --help

Options:
  -h --help  Display this help information.
HEREDOC
}

###############################################################################
# Options
#
# NOTE: The `getops` builtin command only parses short options and BSD `getopt`
# does not support long arguments (GNU `getopt` does), so the most portable
# and clear way to parse options is often to just use a `while` loop.
#
# For a pure bash `getopt` function, try pure-getopt:
#   https://github.com/agriffis/pure-getopt
#
# More info:
#   http://wiki.bash-hackers.org/scripting/posparams
#   http://www.gnu.org/software/libc/manual/html_node/Argument-Syntax.html
#   http://stackoverflow.com/a/14203146
#   http://stackoverflow.com/a/7948533
#   https://stackoverflow.com/a/12026302
#   https://stackoverflow.com/a/402410
###############################################################################

# Parse Options ###############################################################

# Initialize program option variables.
_PRINT_HELP=0
_USE_DEBUG=0

# Initialize additional expected option variables.
_OPTION_X=0
_SHORT_OPTION=
_LONG_OPTION=

# __get_option_value()
#
# Usage:
#   __get_option_value <option> <value>
#
# Description:
#  Given a flag (e.g., -e | --example) return the value or exit 1 if value
#  is blank or appears to be another option.
__get_option_value() {
  local __arg="${1:-}"
  local __val="${2:-}"

  if [[ -n "${__val:-}" ]] && [[ ! "${__val:-}" =~ ^- ]]
  then
    printf "%s\\n" "${__val}"
  else
    _exit_1 printf "%s requires a valid argument.\\n" "${__arg}"
  fi
}

while ((${#}))
do
  __arg="${1:-}"
  __val="${2:-}"

  case "${__arg}" in
    -h|--help)
      _PRINT_HELP=1
      ;;
    --debug)
      _USE_DEBUG=1
      ;;
    -x|--option-x)
      _OPTION_X=1
      ;;
    -o)
      _SHORT_OPTION="$(__get_option_value "${__arg}" "${__val:-}")"
      shift
      ;;
    --long-option)
      _LONG_OPTION="$(__get_option_value "${__arg}" "${__val:-}")"
      shift
      ;;
    --endopts)
      # Terminate option parsing.
      break
      ;;
    -*)
      _exit_1 printf "Unexpected option: %s\\n" "${__arg}"
      ;;
  esac

  shift
done

###############################################################################
# Main
###############################################################################

# _main()
#
# Usage:
#   _main [<options>]
#
# Description:
#   Entry point for the program, handling basic option parsing and dispatching.
_main() {
  if ((_PRINT_HELP))
  then
    _print_help
  else
    if type -t wevtutil &> /dev/null
    then
        printf "Windows\\n"
    elif type -t scutil &> /dev/null
    then
        printf "Mac\\n"
    else
        printf "Linux\\n"
    fi
  fi
}

# Call `_main` after everything has been defined.
_main "$@"