A shell library for parsing arguments

argparse.sh

# parse --my_option into the MY_OPTION variable
# also handles positional arguments

__args_list=()
__required_args_list=()
__unexport_args_list=()

normalize_argument() {
    # uppercase
    local argname="${1^^}"
    # replace - by _
    printf '%s\n' "${argname}" | tr - _
}

assign_var() {
    # printf can assign variables
    printf -v "$1" '%s' "$2"
}

# public arguments get forwarded through the environment
public_optional_argument() {
    local argname="$(normalize_argument "$1")"
    __args_list+=( "${argname}" )
    assign_var "__args_${argname}" 1
}

public_required_argument() {
    local argname="$(normalize_argument "$1")"
    assign_var "__args_${argname}" 1
    __args_list+=( "${argname}" )
    __required_args_list+=( "${argname}" )
}

optional_argument() {
    local argname="$(normalize_argument "$1")"
    assign_var "__args_${argname}" 1
    __args_list+=( "${argname}" )
    __unexport_args_list+=( "${argname}" )
}

required_argument() {
    local argname="$(normalize_argument "$1")"
    assign_var "__args_${argname}" 1
    __args_list+=( "${argname}" )
    __required_args_list+=( "${argname}" )
    __unexport_args_list+=( "${argname}" )
}

undefined_variable() {
    [ "${!1+x}" == '' ]
}

__positional_arg_count=0
positional_argument() {
    assign_var "__positional_arg_$((__positional_arg_count++))" "$(normalize_argument "$1")"
}

__arguments_parsed=0
log_command() {
    if [ "${__arguments_parsed}" = 0 ]; then
        error "call parse_arguments before log_command"
        exit 1
    fi

    local argname

    # print the environment variables
    for argname in "${__args_list[@]}"; do
        if ! undefined_variable "$argname"; then
            printf '%s=%q ' "$argname" "${!argname}"
        fi
    done

    # print the script path
    printf '%s' "$0"

    # print the positional arguments
    if [ "${#positional_arguments[@]}" != 0 ]; then
        printf '%s' ' --'
        printf ' %s' "${positional_arguments[@]}"
    fi

    printf '\n'
}

parse_arguments() {
    __arguments_parsed=1
    while [ $# != 0 ]; do
        local argument="$1"
        if [ "$argument" = '--' ]; then
            shift
            positional_arguments=( "$@" )
            break
        fi

        case "$argument" in
            --*)
                local argname="$(normalize_argument "${argument#--}")"
                local slotname="__args_${argname}"
                if [ "${!slotname}" != '1' ]; then
                    error "unknown named argument: $argument ($argname)"
                    exit 1
                fi

                if [ $# -lt 2 ]; then
                    error "missing value for parameter ${argname}"
                    exit 1
                fi

                shift
                assign_var "$argname" "$1" ;;
            *)  # when meeting a non option argument, stop parsing
                positional_arguments=( "$@" )
                break ;;
        esac

        shift
    done

    # error out when there are too many positional arguments
    local pos_arg_count="${#positional_arguments[@]}"
    if [ "${pos_arg_count}" -gt "${__positional_arg_count}" ]; then
        error "too many positional arguments"
        exit 1
    fi

    # error out when there are too few positional arguments
    if [ "${pos_arg_count}" -lt "${__positional_arg_count}" ]; then
        for ((i=pos_arg_count; i < __positional_arg_count; i++)); do
            local arg_name_var="__positional_arg_$i"
            error "missing positional argument: ${!arg_name_var}"
        done
        exit 1
    fi

    # assign positional argument variables
    for ((i=0; i < __positional_arg_count; i++)); do
        local arg_name_var="__positional_arg_$i"
        local arg_name="${!arg_name_var}"
        assign_var "${arg_name}" "${positional_arguments[i]}"
    done

    # detect missing mandatory arguments
    for arg in "${__required_args_list[@]}"; do
        if undefined_variable "$arg"; then
            error "missing required argument: $arg"
            exit 1
        fi
    done

    # unexport arguments
    for arg in "${__unexport_args_list[@]}"; do
        export -n "$arg"
    done
}