cal—Displays a calendar
cal [–jy] [month [year]]
cal displays a simple calendar. If arguments are not specified, the current month is displayed. The options are as follows:
–j Display Julian dates (days one-based, numbered from January 1)
–y Display a calendar for the current year
A single parameter specifies the year (1–9999) to be displayed; note the year must be fully specified:
will not display a calendar for 1989. Two parameters denote the month (1–12) and year. If no parameters are specified, the current month’s calendar is displayed.
A year starts on Jan 1.
The Gregorian Reformation is assumed to have occurred in 1752 on the 3rd of September. By this time, most countries had recognized the reformation (although a few did not recognize it until the early 1900s.) Ten days following that date were eliminated by the reformation, so the calendar for that month is a bit unusual.