jcal

Display a calendar for the current month

$ jcal

$ jcal -3

$ jcal [year]

$ jcal [year] [month]

jcal [-jy] [[[month] year]]

-j
    Display Julian dates (default).

-y
    Display the entire year.

month
    The month to display (1-12). If omitted, the current month is shown.

year
    The year to display. If omitted, the current year is shown.

The jcal command is a simple utility in Linux systems, similar to the standard cal command, but it displays Julian dates alongside the standard Gregorian calendar. Julian dates represent the number of days elapsed since a specific epoch (usually January 1, 4713 BC in the Julian proleptic calendar). jcal can be used to show the current month's calendar, a specific month and year, or an entire year. It is useful for those who work with Julian dates for scientific, astronomical, or historical purposes.

Its basic function is to output a human-readable calendar representation, making it easier to relate Gregorian dates to their corresponding Julian date equivalents. It helps bridge the gap between standard calendar usage and contexts where Julian date representation is necessary or preferred. The user can choose to display a single month or the entire year's calendars.

jcal: Display the current month's calendar with Julian dates.
jcal 1 2024: Display January 2024's calendar with Julian dates.
jcal -y 2024: Display the entire year of 2024's calendar with Julian dates.

jcal is a derivative of the standard cal utility, modified to include the display of Julian dates. Its development likely stemmed from the need to easily correlate Gregorian calendar dates with their Julian day number equivalents, commonly used in scientific fields. Its usage has been mostly consistent, serving as a straightforward command for presenting calendar information with Julian date extensions.

cal(1), date(1)