[Bash] Dynamically expanded bash menu that can call any function

template.bash

#!/bin/bash

shopt -s extglob

SCRIPT_NAME="$(basename $0)"
LOG_FILE="${0%.*}.log"

DATE_FORMAT="%F %H:%M:%S %z"

PID_MAX="$(cat /proc/sys/kernel/pid_max)"
PID_FORMAT="%${#PID_MAX}d"                  # if $PID_MAX=32767 ---> %5d
PID_INFO="$(printf "${PID_FORMAT}" $$)"

exit_log()
{
    log "$@"
    exit 1
}

get_function_list()
{
    local function_list=($(compgen -A function))

    remove_reserved_function_from_list # use the same variable 'function_list'

    local IFS="|"
    echo "${function_list[*]}"
}

log()
{
    echo -e "[${PID_INFO}][$(date +"$DATE_FORMAT")] $@" | tee -a ${LOG_FILE}
}

main()
{
    local function="${1}"
    shift

    local available_functions
    # get_function_list returns a list of function names separated by |,
    # then annotated with bash extglob to make dynamic expansion case work
    available_functions="$(get_function_list)" || exit_log "get_function_list failed($?)"
    available_functions="+(${available_functions})"

    case "${function}" in
        start)
            "${function}" "$@"
            ;;

        stop)
            "${function}" "$@"
            ;;

        ${available_functions[*]})
            "${function}" "$@"
            ;;

        *)
            usage
            ;;
    esac
}

start()
{
    log "[${FUNCNAME}] begin"

    log "[${FUNCNAME}] end"
}

stop()
{
    log "[${FUNCNAME}] begin"

    log "[${FUNCNAME}] end"
}

remove_reserved_function_from_list()
{
    # use caller function's variable '$function_list' in this function

    local reserve_functions=("main" "get_function_list" "remove_reserved_function_from_list")

    for reserve_function in "${reserve_functions[@]}"; do
        for ((index=0; index<"${#function_list[@]}"; index++)); do
            if [ "${reserve_function}" == "${function_list[${index}]}" ]; then
                unset function_list["${index}"]
                break
            fi
        done
    done
}

usage()
{
    exit_log "Usage: ${SCRIPT_NAME} [$(get_function_list)]"
}

main "$@"