cal

What it does

cal prints a simple text calendar to the terminal. With no arguments it shows the current month, highlighting today's date. Given a year, it prints all twelve months of that year; given both a month and year, it prints just that specific month — a fast way to check dates without opening a graphical calendar app.

Beginner examples

• cal — show the current month, with today highlighted
• cal 2026 — show every month of the year 2026
• cal 7 2026 — show July 2026 specifically
• cal -3 — show last month, this month, and next month together

cal -3

Advanced examples

• Print the entire current year at a glance: cal -y
• Check what day of the week a specific future date falls on: cal 12 2026 and scan for the date
• Show Julian day-of-year numbers instead of calendar days: cal -j
• Quickly verify month boundaries when scripting date-based logic by cross-checking against cal -3
• Combine with date to confirm "today" lines up with what cal highlights: date +%F; cal

cal -y

Common mistakes

• Typing cal 2026 expecting July 2026 and getting the entire year instead — a single numeric argument is interpreted as a year, not a month; you need cal 7 2026 for a specific month.
• Confusing week-start conventions between locales/systems — some configurations start the week on Sunday, others on Monday, which can make date columns look "off" if you're not expecting it.
• Assuming cal's single-argument year behavior is universal across all cal implementations without testing — BSD and util-linux versions can differ slightly in argument parsing and defaults.

Tips

• Use cal -3 when working out date math near a month boundary (e.g. "is the 30th a Friday, and what's the first Monday of next month?").
• cal -y is a handy quick reference for annual planning without opening a full calendar application.
• Pipe cal's output into grep (with color) to visually spot a specific day number quickly in a big block of text, though highlighting today only works in the live terminal, not through a pipe.

Best practices

• Prefer cal -3 or cal -y over repeatedly re-running plain cal with different month/year arguments when comparing nearby dates — it reduces context-switching.
• When scripting date logic, don't parse cal's visual output — use date with format strings instead; cal is meant for human viewing, not machine parsing.
• Be explicit with both month and year (cal 7 2026) rather than relying on defaults when precision matters, since a bare cal <number> is always interpreted as a year.

Real-world use cases

• Quickly checking what day of the week a specific date falls on when scheduling a meeting or deployment.
• Glancing at the upcoming month's layout to plan a release calendar directly from the terminal.
• Verifying date-related assumptions while writing or debugging scripts that compute "next Monday" or "last day of the month".

Common interview questions

• How do you display a specific month and year with cal? cal <month> <year>, e.g. cal 7 2026 for July 2026 — a single numeric argument alone is interpreted as a full year.
• How would you view three consecutive months at once? cal -3, which shows the previous, current, and next month side by side.
• Is cal suitable for use in scripts that need to compute dates? Not really — it's designed for human-readable display; date with format strings and arithmetic (-d) is the right tool for programmatic date calculations.