CRON Syntax

CRON is a job scheduler, it enables automation of tasks execution at specified time intervals.

A CRON is usually made of six required fields, as seen below.

Shooju uses APScheduler, which supports the following expression types:

Expression	Field	Description	Example
*	any	Runs on every value	An asterisk in the minute field is equivalent to run every minute
a/b	any	Skips a given number of values	*/3 in the hour field corresponds to run every three hours
a-b	any	Runs on a specified range of values	1-4 in the day (week) field is equivalent to only run Tuesdays to Fridays
a,b	any	Runs on a specified list of values	Running every day at 15 and 23 corresponds to 15,23 in the hour field
`xth_y`	day	Fire on the `x` -th occurrence of weekday `y` within the month
`last_x`	day	Fire on the last occurrence of weekday `x` within the month
last	day (month)	Runs on last day of the month

Cron	Description
15 30 4 * * MON	at 4:30:15 on every Monday
* * /2 * *	every two hours
* 0 8,10,15 1-5 * *	at 8, 10 and 15 on first five days of the month
15 30 5 last * *	at 5:30:15 on every last day of the month
0 0 5 1st_fri * *	at 5:00:00 on every first friday of the month
0 0 5 last_sun * *	at 5:00:00 on every last sunday of the month
* * * 1-7 * 5	first saturday of the month

Note that jobs between 12 am and 1 am may cause a skip or repeat job schedule depending on CRON timezone

Bear in mind external helpers such as https://crontab.guru/ and http://www.cronmaker.com/ are available for guidance but may not reflect same syntax as supported by Shooju