jcal

Display a calendar for the current month

$ jcal

$ jcal -3

$ jcal [year]

$ jcal [year] [month]

jcal [-3hjy] [[month] year]

-3
    Display previous, current, and next month side-by-side

-h
    Start weeks on Monday (ignored with -y)

-j
    Show Julian day numbers (days since Jan 1, Year 1)

-y
    Display calendar for entire specified year

The jcal command is a simple command-line tool for displaying calendars in the Julian calendar system, which was introduced by Julius Caesar in 46 BCE and used widely until the Gregorian reform in 1582. Unlike the Gregorian calendar, it approximates the solar year as 365.25 days by adding a leap day every four years, causing a gradual drift of about 11 minutes per year.

jcal outputs a textual representation similar to the standard cal command but with dates adjusted to the Julian reckoning. By default, it shows the current month, converting the present Gregorian date to its Julian equivalent. Users can specify a month (1-12) and year (1 or greater) for historical or astronomical purposes.

Key features include multi-month views, week header customization, and optional Julian day numbers (days since January 1, Year 1). It's useful for historians, astronomers, or anyone studying pre-modern chronology. Available in Linux via the bsdmainutils package, it provides precise conversions without external dependencies.

Julian dates diverge from Gregorian after 1582; modern usage is historical/astronomical only. Years before 1 CE not supported.

Without arguments, shows current month in Julian calendar.
Example: jcal

jcal 2 44 → February, Year 44 BCE (Julian).
jcal -3 → Three months around current.
jcal -y 1752 → Full year 1752.

Originated in 4.3BSD Unix (1986) as part of cal utilities; ported to Linux in bsdmainutils package since ~1990s for compatibility.

cal(1)