Oracle Rdb saves and allows you to access up to 20 of your most
    recently entered RDO commands. Use the UP-ARROW or CTRL/B keys
    to recall previously entered commands. Use the DOWN-ARROW key
    to reexamine a command that you had retrieved using the UP-ARROW
    key.

    This feature is designed for the convenience of RDO users. It
    greatly reduces the need to enter the RDO editing buffer to
    rerun one or more of your last 20 commands. The EDIT statement
    continues to be a useful tool for created RDO procedures in that
    it lets you take advantage of your editor's text manipulation
    features and it lets you edit multiple lines.

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    Any string entered at the RDO> prompt is saved in the recall
    buffer. This includes all DCL commands prefaced by the dollar
    sign ($), commented text that begins with the exclamation
    point (!), and any RDO statements. The carriage return delimits
    each line written to the recall buffer. Thus, in the following
    example, four separate entries are written to the recall buffer:

    RDO> FOR E IN EMPLOYEES
    cont> WITH E.EMPLOYEE_ID BETWEEN "00164" AND "00175"
    cont> PRINT E.LAST_NAME, E.EMPLOYEE_ID
    cont> END_FOR

    The most recently typed command is at the top of the recall
    buffer. If the user enters CTRL/B at this point, the END_FOR
    statement would appear first.

    There are no parameters or logicals available to control the
    maximum number of lines saved in the recall buffer.