CronJob Expressions

Introduction

Cron-Expressions are used to configure schedules. Cron-Expressions are strings that are actually made up of seven sub-expressions, that describe individual details of the schedule. These sub-expression are separated with white-space, and represent:

  1. Seconds
  2. Minutes
  3. Hours
  4. Day-of-Month
  5. Month
  6. Day-of-Week

Individual sub-expressions can contain ranges and/or lists.

Wild-cards (the ‘‘ character) can be used to say “every” possible value of this field. Therefore the ‘‘ character in the “Month” field of the previous example simply means “every month”. A ‘*’ in the Day-Of-Week field would therefore obviously mean “every day of the week”.

All of the fields have a set of valid values that can be specified. These values should be fairly obvious – such as the numbers 0 to 59 for seconds and minutes, and the values 0 to 23 for hours. Day-of-Month can be any value 1-31, but you need to be careful about how many days are in a given month! Months can be specified as values between 0 and 11. Days-of-Week can be specified as values between 1 and 7 (1 = Sunday).

The ‘/’ character can be used to specify increments to values. For example, if you put ‘0/15’ in the Minutes field, it means ‘every 15th minute of the hour, starting at minute zero’. If you used ‘3/20’ in the Minutes field, it would mean ‘every 20th minute of the hour, starting at minute three’ – or in other words it is the same as specifying ‘3,23,43’ in the Minutes field. Note the subtlety that “/35″ does *not mean “every 35 minutes” – it mean “every 35th minute of the hour, starting at minute zero” – or in other words the same as specifying ‘0,35’.

The ‘?’ character is allowed for the day-of-month and day-of-week fields. It is used to specify “no specific value”. This is useful when you need to specify something in one of the two fields, but not the other.

Example Cron Expressions

Example 1 – an expression to create a trigger that simply fires every 5 minutes

“0 0/5 * * * ?”

Example 2 – an expression to create a trigger that fires every 5 minutes, at 10 seconds after the minute (i.e. 10:00:10 am, 10:05:10 am, etc.).

“10 0/5 * * * ?”

Example 3 – At 10 seconds of every even minute

“10 */2 * ? * *”

Example 4 – At 10 seconds of every odd minute

“10 1-59/2 * ? * *”

Example 5 – Every 5 minutes, Weekdays from 8-5.

“0 */5 8-16 ? * 2-6”

Cron is a UNIX tool that has been around for a long time, so its scheduling capabilities are powerful and proven. The CronJobr class is based on the scheduling capabilities of cron.

CronJob uses “cron expressions”, which are able to create firing schedules such as: “At 8:00am every Monday through Friday” or “At 1:30am every last Friday of the month”.

Cron expressions are powerful, but can be pretty confusing. This tutorial aims to take some of the mystery out of creating a cron expression, giving users a resource which they can visit before having to ask in a forum or mailing list.

Format

Field Mandatory Allowed Values Allowed Special Characters
Seconds YES 0-59 , – * /
Minutes YES 0-59 , – * /
Hours YES 0-23 , – * /
Day of the Month YES 1-31 , – * ? / L W
Month YES 1-12 or JAN-DEC , – * /
Day of week YES 1-7 or SUN-SAT , – * ? / L #
Year NO empty, 1970-2099 , – * /

Examples

Expression Meaning
0 0 12 * * ? Fire at 12pm (noon) every day
0 15 10 ? * * Fire at 10:15am every day
0 15 10 * * ? Fire at 10:15am every day
0 15 10 * * ? * Fire at 10:15am every day
0 15 10 * * ? 2005 Fire at 10:15am every day during the year 2005
0 * 14 * * ? Fire every minute starting at 2pm and ending at 2:59pm, every day
0 0/5 14 * * ? Fire every 5 minutes starting at 2pm and ending at 2:55pm, every day
0 0/5 14,18 * * ? Fire every 5 minutes starting at 2pm and ending at 2:55pm, AND fire every 5 minutes starting at 6pm and ending at 6:55pm, every day
0 0-5 14 * * ? Fire every minute starting at 2pm and ending at 2:05pm, every day
0 10,44 14 ? 3 WED Fire at 2:10pm and at 2:44pm every Wednesday in the month of March.
0 15 10 ? * MON-FRI Fire at 10:15am every Monday, Tuesday, Wednesday, Thursday and Friday
0 15 10 15 * ? Fire at 10:15am on the 15th day of every month
0 15 10 L * ? Fire at 10:15am on the last day of every month
0 15 10 ? * 6L Fire at 10:15am on the last Friday of every month
0 15 10 ? * 6L Fire at 10:15am on the last Friday of every month
0 15 10 ? * 6L 2002-2005 Fire at 10:15am on every last friday of every month during the years 2002, 2003, 2004 and 2005
0 15 10 ? * 6#3 Fire at 10:15am on the third Friday of every month
0 0 12 1/5 * ? Fire at 12pm (noon) every 5 days every month, starting on the first day of the month.
0 11 11 11 11 ? Fire every November 11th at 11:11am.

Reference

For more information, refer to the Cron Expression Generator and Explainer.