Apart from the usual and well known calendar functions like the output of a month or a year calendar sheet, or the output of an eternal holiday list, Gcal, the Gregorian calendar program of the Free Software Foundation, offers the facility to display fixed dates on the day of their occurrence and to remind or inform the user about them. So it is imaginable after booting the computer or starting the work session, that the user is informed on screen or by means of electronic mail about all holidays or appointments which are observed or scheduled for that day.
The period, for which Gcal respects occurring fixed dates, may be freely selected by the user. So it is possible that Gcal displays all fixed dates which occur on tomorrow’s date, the whole week, the whole month or in the whole year. Fixed dates which occur on a selected date of the year, and those that occur relative to another given date, are displayed either related to this single date only, or in listed manner starting on this date and ending on the actual date3.
There are two methods to display a preview of fixed dates4 or retrospective view of fixed dates5. On the one hand, Gcal can be started by using an option that sets the system date of the computer to the given date during the time of the program execution with the result, the program assumes the system date is set to this given date and the user can define any needed period that should be respected by an option. On the other hand, Gcal can be started with a command which forces the program to use a different year instead of the actual year, so Gcal will display all occurring fixed dates for this particular year. But this limits the user in that it disables defining any needed period by an option, because the period is always set to the whole year by default.
Gcal isn’t only able to display fixed dates which are stored for a concrete date, e.g. ‘Fixed date on 1st December 1995’, rather than fixed dates occurring periodically again and again. So it is possible to define repeated events like ‘This fixed date occurs every day in May 1995’ or ‘Every 15th November in any years’. These fixed date definitions are stored in resource files and whenever Gcal is started, an option to evaluate the necessary resource files can be given.
Once the user has set his/her preferred command line arguments for querying the fixed dates data base, it is possible to store them in a response file or shell script file. A response file contains all arguments delivered to Gcal, but unlike a shell script file, such a response file isn’t executable; it is only a pool of command line arguments which can be preloaded if needed. A shell script file can be started and calls Gcal directly with all arguments stored in it and all arguments which are given further in the command line.
A list of all usable command line arguments and their descriptions can be found in the next chapter, which helps one to use Gcal in the most efficient and productive way possible. After it follows the description how to use the eternal holiday list, and in the succeeding chapter, how to use the fixed date list. Comprehensive explanations respectively summaries and tables to definite details or themes from other disciplines can be found in the numerous appendices.