var_store()
{
        trap '' INT

        while read -r command arg1 arg2 arg3
        do
                case ${command} in

                        WRITE)
                                declare ${arg1}=${arg2}
                                printf "${arg1}=${arg2}\n" > ${arg3}
                                ;;
                        READ)
                                if [[ -v "${arg1}" ]]
                                then
                                        printf "${!arg1}\n" > ${arg2}
                                else
                                        printf "unset\n" > ${arg2}
                                fi
                                ;;
                        *)
                                printf '%s\n' "Unknown command: ${command}" >&2
                                ;;

                esac

        done < ${var_store_input_fifo}
}

var_store_write()
{
        local var_name=${1}
        local var_value=${2}

        echo "writing $var_store_input_fifo"

        printf "WRITE ${var_name} ${var_value} ${var_store_output_fifo}\n" > ${var_store_input_fifo}

        echo "written"

        read -r write_confirmation < ${var_store_output_fifo}

        echo $write_confirmation

        if [[ "${write_confirmation}" != "${var_name}=${var_value}" ]]
        then
                printf '%s\n' "var_store write error: var_name=${var_name}; var_value=${var_value}; write_confirmation=${write_confirmation}" >&2
        fi
}

var_store_read()
{
        local -n var_name=${1}
        local -n var_dest=${2:-${1}}
        local exit_on_unset=${3:-1}

        printf "READ ${!var_name} ${var_store_output_fifo}\n" > ${var_store_input_fifo}

        read -r var_dest < ${var_store_output_fifo}

        if [[ "${var_dest}" == "unset" ]]
        then
                if ((exit_on_unset))
                then
                        printf '%s\n' "${!var_name} unset and exit_on_unset enabled." >&2
                        kill -$$ INT
                else
                        return 1
                fi
        fi
}

var_store_link()
{
        local path=${1}
        local name=${2}

        var_store_output_fifo="${path}/${name}_var_store_output_fifo"
        [[ -p ${var_store_output_fifo} ]] && printf '%s\n' "${name} already linked" >&2
        mkfifo ${var_store_output_fifo}
}

var_store_unlink()
{
        [[ -p ${var_store_output_fifo} ]] && rm ${var_store_output_fifo}
}