cal - displays a calendar
cal [-smjy13 ] [[ month ] year ]
Cal displays a simple calendar. If arguments are not specified, the current month is displayed. The options are as follows:
Display single month output. (This is the default.)
Display prev/current/next month output.
Display Sunday as the first day of the week. (This is the default.)
Display Monday as the first day of the week.
Display Julian dates (days one-based, numbered from January 1).
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: ``cal 89 '' 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 1900's.) Ten days following that date were eliminated by the reformation, so the calendar for that month is a bit unusual.

A cal command appeared in Version 6 AT&T UNIX.