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How the program deals with input

Character strings separated by spaces are entered at the User Console and sent to the program USER by pressing RETURN. USER's command processor first attempts to identify the first string as a command name by comparing it with its internal dictionary of such names. If it is successful in making a match, one of two things may happen: a command which does not take any arguments (e.g. GO) is executed immediately; however, if the command takes arguments (e.g. RA), the program will go on processing the input line until the requisite number of acceptable arguments have been analysed, at which time the command is executed. If the input line is not exhausted the next character string delimited by spaces is processed in the same manner. When the command processor is not able to match a character string with a command name, the program outputs a message and ignores the rest of the input line. Commands may have up to 7 qualifiers and 5 parameters. Most require a control panel button to be pushed for any action to occur. The full specification of an action could therefore be of the form:


followed by pressing a control panel button. Note that occasionally parameters are associated with only one qualifier. Section 2.2 gives a complete list of commands, their qualifiers, parameters and any required control panel interaction. For all commands which take qualifiers the first given is the default. If the user interface requires a parameter which has not been specified it will request it with the prompt:


If you have changed your mind and don't want to give a value, just press Return and the old value is kept.

Tue Aug 5 05:37:08 MET DST 1997