Bash argument parsing example

bash-argument-parsing.sh

#!/bin/bash
set -o errexit # Fail and exit the script immediately if any command fails
set -o nounset # Throw an error if there are unset variables

# Parse arguments (based on https://stackoverflow.com/questions/192249/how-do-i-parse-command-line-arguments-in-bash)
HARD="false"
VERBOSE="false"

usage_error () { echo >&2 "$(basename ${0}):  ${1}"; exit 2; }
assert_argument () { test "${1}" != "${EOL}" || usage_error "${2} requires an argument"; } # TODO: Force boolean

if [ "${#}" != 0 ]; then
  EOL=$(printf '\1\3\3\7')
  set -- "${@}" "${EOL}"
  while [ "${1}" != "${EOL}" ]; do
    OPT="${1}"; shift
    case "${OPT}" in
      -h|--help)
        echo 
        echo "Usage: ${0} (options)"
        echo 
        echo "Options:"
        echo "  -a, --hard                    Hard reset, wiping all persisted user data"
        echo "  -v, --verbose                 Provide extra output to aid debugging"
        echo
        exit 1
      ;;

      # Variables
      -a|--hard )     HARD="true";;
      -v|--verbose )  VERBOSE="true";;
      
      # Arguments processing. You may remove any unneeded line after the 1st.
      -|''|[!-]*)     set -- "${@}" "${OPT}";;                                          # positional argument, rotate to the end
      --*=*)          set -- "${OPT%%=*}" "${OPT#*=}" "$@";;                        # convert '--name=arg' to '--name' 'arg'
      -[!-]?*)        set -- $(echo "${OPT#-}" | sed 's/\(.\)/ -\1/g') "$@";;       # convert '-abc' to '-a' '-b' '-c'
      --)             while [ "${1}" != "${EOL}" ]; do set -- "$@" "${1}"; shift; done;;  # process remaining arguments as positional
      -*)             usage_error "unknown option: '${OPT}'";;                        # catch misspelled options
      *)              usage_error "this should NEVER happen (${OPT})";;               # sanity test for previous patterns

    esac
  done
  shift 
fi

# Preflight checks
if [ ! -z "$@" ]; then # Abort if bad argument given
    echo "Unexpected arguments '${@}'" >&2
    exit 1
fi