CRON Expressions¶

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Expression Syntax

Format
Field Values

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 * * * *

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