The CLI$DCL_PARSE routine supplies a command string to DCL for
    parsing. DCL parses the command string according to the syntax in
    the command table specified in the table argument.

    The CLI$DCL_PARSE routine can prompt for required parameters if
    you specify a parameter routine in the routine call. In addition,
    the CLI$DCL_PARSE routine can prompt for entire or continued
    command lines if you supply the address of a prompt routine.

    If you do not specify a command string to parse and the user
    enters a null string in response to the DCL prompt for a command
    string, CLI$DCL_PARSE immediately terminates and returns the
    status CLI$_NOCOMD.

    If DCL prompts for a required parameter and the user presses
    Ctrl/Z, CLI$DCL_PARSE immediately terminates and returns the
    status CLI$_NOCOMD, regardless of whether you specify or do not
    specify a command string to parse. If DCL prompts for a parameter
    that is not required and the user presses Ctrl/Z, CLI$DCL_PARSE
    returns the status CLI$_NORMAL.

    Whenever CLI$DCL_PARSE encounters an error, it both signals and
    returns the error.