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CRON Expressions

CRON expressions are user-defined strings that use standard cron job syntax to define when a scheduled trigger should execute. Whenever all of the fields in a CRON expression match the current date and time, Atlas fires the trigger associated with the expression.

Expression Syntax

Format

CRON expressions are strings composed of five space-delimited fields. Each field defines a granular portion of the schedule on which its associated trigger executes:

* * * * *
│ │ │ │ └── weekday...........[0 (SUN) - 6 (SAT)]
│ │ │ └──── month.............[1 (JAN) - 12 (DEC)]
│ │ └────── dayOfMonth........[1 - 31]
│ └──────── hour..............[0 - 23]
└────────── minute............[0 - 59]
Field Valid Values Description
minute [0 - 59]

Represents one or more minutes within an hour.

Example

If the minute field of a CRON expression has a value of 10, the field matches any time ten minutes after the hour (e.g. 9:10 AM).

hour [0 - 23]

Represents one or more hours within a day on a 24-hour clock.

Example

If the hour field of a CRON expression has a value of 15, the field matches any time between 3:00 PM and 3:59 PM.

dayOfMonth [1 - 31]

Represents one or more days within a month.

Example

If the dayOfMonth field of a CRON expression has a value of 3, the field matches any time on the third day of the month.

month
1  (JAN) 7  (JUL)
2  (FEB) 8  (AUG)
3  (MAR) 9  (SEP)
4  (APR) 10 (OCT)
5  (MAY) 11 (NOV)
6  (JUN) 12 (DEC)

Represents one or more months within a year.

A month can be represented by either a number (e.g. 2 for February) or a three-letter string (e.g. APR for April).

Example

If the month field of a CRON expression has a value of 9, the field matches any time in the month of September.

weekday
0 (SUN)
1 (MON)
2 (TUE)
3 (WED)
4 (THU)
5 (FRI)
6 (SAT)

Represents one or more days within a week.

A weekday can be represented by either a number (e.g. 2 for a Tuesday) or a three-letter string (e.g. THU for a Thursday).

Example

If the weekday field of a CRON expression has a value of 3, the field matches any time on a Wednesday.

Field Values

Each field in a CRON expression can contain either a specific value or an expression that evaluates to a set of values. The following table describes valid field values and expressions:

Expression Type Description
All Values
(*)

Matches all possible field values.

Available in all expression fields.

Example

The following CRON expression schedules a trigger to execute once every minute of every day:

* * * * *
Specific Value
(<Value>)

Matches a specific field value. For fields other than weekday and month this value will always be an integer. A weekday or month field can be either an integer or a three-letter string (e.g. TUE or AUG).

Available in all expression fields.

Example

The following CRON expression schedules a trigger to execute once every day at 11:00 AM UTC:

0 11 * * *
List of Values
(<Expression1>,<Expression2>,...)

Matches a list of two or more field expressions or specific values.

Available in all expression fields.

Example

The following CRON expression schedules a trigger to execute once every day in January, March, and July at 11:00 AM UTC:

0 11 * 1,3,7 *
Range of Values
(<Start Value>-<End Value>)

Matches a continuous range of field values between and including two specific field values.

Available in all expression fields.

Example

The following CRON expression schedules a trigger to execute once every day from January 1st through the end of April at 11:00 AM UTC:

0 11 * 1-4 *
Modular Time Step
(<Field Expression>/<Step Value>)

Matches any time where the step value evenly divides the field value with no remainder (i.e. when Value % Step == 0).

Available in the minute and hour expression fields.

Example

The following CRON expression schedules a trigger to execute on the 0th, 25th, and 50th minutes of every hour:

*/25 * * * *