cal – print calendar
prints a calendar.
is either a number from 1 to 12,
a lower case month name,
or a lower case three-letter prefix of a month name.
can be between 1
is omitted, the current month or year is used.
If only one argument is given, and it is a number larger than 12,
a calendar for all twelve months of the given year is produced;
otherwise a calendar for just one month is printed.
produced is that for England and her colonies.
cal sep 1752
The year is always considered to start in January even though this
is historically naive.
refers to the early Christian era,
not the 20th century.