Input and output considerations (2)
Defaults defaults should be provided to minimise typing requirements and to facilitate learning. [EXAMPLE if the disk drive is not identified it is assumed to be the currently set default drive] [NOTE arguments that have default parameter values are often referred to as optional arguments
Destructive commands (a) if a command may have unintentional or destructive consequences (e.g. delete a file): the user should be allowed to cancel or undo the previous (last) command and its effects; (b) the user should be required to confirm the intention of the command before command execution.
Customisation if system constrains allow, users should have the capability to designate and use synonyms for commands and command macros and they should be able to revert back to the default names when desired.
Echoing typed commands (a) the user’s input should be displayed (echoed) in a consistent position; (b) typed in command characters should be displayed (echoed) as the user types each character. [EXAMPLE (a) displayed on a ‘command line’ at the bottom of the screen or displayed after the prompt on the screen]
Output control if appropriate to the task and system constrains allow, the command phrase should allow arguments for redirecting output, interrupting output, or stopping output.
Consistent output format commands resulting in similar or related output should present their resulting data in a consistent format. [EXAMPLE use of a single presentation format for lists of files, processes, directories, etc.]