bashism.sh

#!/usr/bin/env bash
# for GNU bash 3.x on Linux

declare PROGRAM_NAME="$(basename "$0")"
declare PROGRAM_DIR="$(realpath "$(dirname "$0")")"

function usage () {
    cat <<EOF
${PROGRAM_NAME} - some nice program

Usage:
  ${PROGRAM_NAME} [-o FILE] [-f] [-v] FILE...

Options:
  -o, --output FILE
  -f, --force
  -F, --no-force
  -v, --verbose
  -h, --help
EOF
}

declare -a FILES=()
declare OUTPUT=
declare -i FORCE=0 VERBOSE=0

function parse_opts () {
    local opt=
    while (( $# )); do
        opt="$1"
        shift
        case "$opt" in
            -o|--output)
                OUTPUT="$1"
                shift
                ;;
            -f|--force)
                FORCE=1
                ;;
            -F|--no-force)
                FORCE=0
                ;;
            -v|--verbose)
                (( VERBOSE+=1 ))
                ;;
            -h|--help)
                usage
                exit 0
                ;;
            --)
                FILES+=("$@")
                shift $#
                ;;
            -)
                FILES+=(-)
                ;;
            -*)
                usage >&2
                echo >&2
                echo >&2 "invalid option: ${opt}"
                exit 1
                ;;
            *)
                FILES+=("$opt")
                ;;
        esac
    done
}

declare -a PREPARED_OPTS=()

function prepare_opts () {
    local opt= char=
    PREPARED_OPTS=()
    while (( $# )); do
        opt="$1"
        shift
        case "$opt" in
            --)
                PREPARED_OPTS+=(-- "$@")
                shift $#
                ;;
            --*)
                # long option
                if [[ $opt =~ ^(--[^=]+)=(.*)$ ]]; then
                    PREPARED_OPTS+=("${BASH_REMATCH[1]}" "${BASH_REMATCH[2]}")
                else
                    PREPARED_OPTS+=("$opt")
                fi
                ;;
            -)
                PREPARED_OPTS+=(-)
                ;;
            -*)
                # short option
                # https://stackoverflow.com/questions/10551981
                while IFS= read -r -d '' -n 1 char; do
                    PREPARED_OPTS+=("-${char}")
                done < <(printf "%s" "${opt#-}")
                ;;
            *)
                PREPARED_OPTS+=("$opt")
                ;;
        esac
    done
}

function main () {
    echo "OUTPUT=${OUTPUT}"
    echo "FORCE=${FORCE}"
    echo "VERBOSE=${VERBOSE}"
    echo "FILES="
    local file=
    for file in "${FILES[@]}"; do
        echo "    ${file}"
    done
}

prepare_opts "$@"
parse_opts "${PREPARED_OPTS[@]}"
main