When running a Cloud Assistant script, you can call an API operation and use the Timed and Frequency parameters to set when to run a Cloud Assistant script. The value of the Frequency parameter is a cron expression. This parameter specifies the frequency of recurring tasks, frequency of routine maintenance, and the point in time to complete a single task.

What is a cron expression?

A cron expression is a string that represents a set of times. The string is separated by five spaces into six fields, in the format of X X X X X X, of which X is a placeholder of a field. If a field contains multiple values, separate the values with commas (,). Each field can be a specific value or special characters with logical representations.

Examples

The following table lists some sample values of cron expressions.

Example Description
0 15 10 ? * * Perform the task at 10:15 every day.
0 15 10 * * ? Perform the task at 10:15 every day.
0 0 12 * * ? Perform the task at 12:00 every day.
0 0 10,14,16 * * ? Perform the task at 10:00, 14:00, and 16:00 every day.
0 0/30 9-17 * * ? Perform the task once every half an hour between 09:00 and 17:00 every day.
0 * 14 * * ? Perform the task once every minute between 14:00 and 14:59 every day.
0 0-5 14 * * ? Perform the task once every minute between 14:00 and 14:05 every day.
0 0/5 14 * * ? Perform the task once every five minutes between 14:00 and 14:55 every day.
0 0/5 14,18 * * ? Perform the task once every five minutes between 14:00 and 14:55 and between 18:00 and 18:55 every day.
0 0 12 ? * WED Perform the task at 12:00 every Wednesday.
0 15 10 15 * ? Perform the task at 10:15 on the 15th day of every month.
0 15 10 L * ? Perform the task at 10:15 on the last day of every month.
0 15 10 ? * 6L Perform the task at 10:15 on the last Friday of every month.
0 15 10 ? * 6#3 Perform the task at 10:15 on the third Friday of every month.
0 10,44 14 ? 3 WED Perform the task between 14:10 and 14:44 every Wednesday in March.

Values for fields

The table lists valid values and supported special characters for each field in cron expressions.

Field Required Value range Special character
Second Yes [0, 59] * , - /
Minute Yes [0, 59] * , - /
Hour Yes [0, 23] * , - /
Day Yes [1, 31] * , - / ? L W
Month Yes [1, 12] or [JAN, DEC] * , - /
Week Yes [1, 7] or [SUN, SAT]. If you use [1, 7], 1 stands for Sunday, and 2 stands for Monday. * , - / ? L #

Special characters

Each field in a cron expression can contain a specific number of special characters. Each special character represents a logical argument.

Special character Description Example
* All possible values. Example: In the Month field, * indicates any month. In the Week field, * indicates any day of a week.
, List enumerated values. Example: In the Minute field, 5,20 indicates that the task is triggered once at both the 5th and 20th minutes.
- Defines a range. Example: In the Minute field, 5-20 indicates that the task is triggered once every minute from the 5th to 20th minute.
/ Specifies increments. Example: In the Minute field, 0/15 indicates that the task is triggered once every 15 minutes from the beginning of an hour. In the Minute field, 3/20 indicates that the task is triggered once every 20 minutes from the 3rd minute of an hour.
? Indicates an unspecified value. Only the Day and Week fields support this character. If either one of the Day and Week fields is specified, the other field must be set to ? to avoid conflicts.
L Indicates "last". Only the Day and Week fields support this character.
Note Do not specify a list or range when using the L character because it may lead to a logical disorder.
  • In the Day field, L indicates the last day of the month. In the Week field, L indicates the last day of a week, namely, Saturday (SAT).
  • If L is preceded by a value, such as 6L in the Week field, it indicates the last Friday of a month.
W The weekday nearest to a given day of the month. The weekday that the W character finalizes on will only be in the same month as the given day. LW indicates the last weekday of the specified month. If 5W is specified in the field and the 5th day of the month falls on Saturday, the task will be triggered on the nearest weekday, which is Friday, the 4th day of a month. If the 5th day of a month falls on Sunday, the task will be triggered on the nearest weekday, which is Monday, the 6th day of the month. If the 5th day of the month falls on a weekday, the task is triggered on the 5th day.
# Indicates a specific day of a specific week in every month. Only the Week field supports this character. Example: In the Week field, 4#2 indicates the 2nd Wednesday of a month.