Question 1

What is cron syntax?

Accepted Answer

Cron is a time-based job scheduler in Unix. A cron expression has 5 fields: minute (0–59), hour (0–23), day-of-month (1–31), month (1–12), and day-of-week (0–7, where 0 and 7 are Sunday). Each field can use *, numbers, ranges (1-5), lists (1,3,5), or steps (*/5).

Question 2

What does */ mean?

Accepted Answer

*/n means "every n units". For example, */15 in the minute field means "every 15 minutes", and */2 in the hour field means "every 2 hours".

Question 3

What are common cron expressions?

Accepted Answer

* * * * * = every minute | 0 * * * * = every hour | 0 0 * * * = daily at midnight | 0 9 * * 1 = every Monday at 9am | 0 0 1 * * = first day of every month

Question 4

How are day-of-month and day-of-week combined?

Accepted Answer

When both day-of-month and day-of-week are non-wildcard, the job runs when either condition is met (OR logic). When only one is non-wildcard, it restricts the schedule.

Cron Expression Parser

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Cron Expression Parser