[[cron-expressions]]
=== Cron expressions

A cron expression is a string of the following form:

[source,txt]
------------------------------
    <seconds> <minutes> <hours> <day_of_month> <month> <day_of_week> [year]
------------------------------

{es} uses the cron parser from the https://quartz-scheduler.org[Quartz Job Scheduler]. 
For more information about writing Quartz cron expressions, see the
http://www.quartz-scheduler.org/documentation/quartz-2.3.0/tutorials/crontrigger.html[Quartz CronTrigger Tutorial].

All schedule times are in coordinated universal time (UTC); other timezones are not supported.

TIP: You can use the <<elasticsearch-croneval>> command line tool to validate your cron expressions.


[[cron-elements]]
==== Cron expression elements

All elements are required except for `year`. 
See <<cron-special-characters>> for information about the allowed special characters.

`<seconds>`::
(Required)
Valid values: `0`-`59` and the special characters `,` `-` `*` `/`

`<minutes>`:: 
(Required)
Valid values: `0`-`59` and the special characters `,` `-` `*` `/`

`<hours>`:: 
(Required)
Valid values: `0`-`23` and the special characters `,` `-` `*` `/`

`<day_of_month>`:: 
(Required)
Valid values: `1`-`31` and the special characters `,` `-` `*` `/` `?` `L` `W`

`<month>`::  
(Required)
Valid values: `1`-`12`, `JAN`-`DEC`, `jan`-`dec`, and the special characters `,` `-` `*` `/`

`<day_of_week>`:: 
(Required)
Valid values: `1`-`7`, `SUN`-`SAT`, `sun`-`sat`,  and the special characters `,` `-` `*` `/` `?` `L` `#`

`<year>`:: 
(Optional)
Valid values: `1970`-`2099` and the special characters `,` `-` `*` `/`

[[cron-special-characters]]
==== Cron special characters

`*`::
Selects every possible value for a field. For
example, `*` in the `hours` field means "every hour".

`?`::                
No specific value. Use when you don't care what the value
is. For example, if you want the schedule to trigger on a
particular day of the month, but don't care what day of
the week that happens to be, you can specify `?` in the
`day_of_week` field.

`-`::                 
A range of values (inclusive). Use to separate a minimum
and maximum value. For example, if you want the schedule
to trigger every hour between 9:00 a.m. and 5:00 p.m., you
could specify `9-17` in the `hours` field.

`,`::
Multiple values. Use to separate multiple values for a
field. For example, if you want the schedule to trigger
every Tuesday and Thursday, you could specify `TUE,THU`
in the `day_of_week` field.

`/`::
Increment. Use to separate values when specifying a time
increment. The first value represents the starting point,
and the second value represents the interval. For example,
if you want the schedule to trigger every 20 minutes
starting at the top of the hour, you could specify `0/20`
in the `minutes` field. Similarly, specifying `1/5` in
`day_of_month` field will trigger every 5 days starting on
the first day of the month.

`L`::
Last. Use in the `day_of_month` field to mean the last day
of the month--day 31 for January, day 28 for February in
non-leap years, day 30 for April, and so on. Use alone in
the `day_of_week` field in place of `7` or `SAT`, or after
a particular day of the week to select the last day of that
type in the month. For example `6L` means the last Friday
of the month. You can specify `LW` in the `day_of_month`
field to specify the last weekday of the month. Avoid using
the `L` option when specifying lists or ranges of values,
as the results likely won't be what you expect.

`W`::
Weekday. Use to specify the weekday (Monday-Friday) nearest
the given day. As an example, if you specify `15W` in the
`day_of_month` field and the 15th is a Saturday, the
schedule will trigger on the 14th. If the 15th is a Sunday,
the schedule will trigger on Monday the 16th. If the 15th
is a Tuesday, the schedule will trigger on Tuesday the 15th.
However if you specify `1W` as the value for `day_of_month`,
and the 1st is a Saturday, the schedule will trigger on
Monday the 3rd--it won't jump over the month boundary. You
can specify `LW` in the `day_of_month` field to specify the
last weekday of the month. You can only use the `W` option
when the `day_of_month` is a single day--it is not valid
when specifying a range or list of days.

`#`::
Nth XXX day in a month. Use in the `day_of_week` field to
specify the nth XXX day of the month. For example, if you
specify `6#1`, the schedule will trigger on the first
Friday of the month. Note that if you specify `3#5` and
there are not 5 Tuesdays in a particular month, the
schedule won't trigger that month.

[[cron-expression-examples]]
==== Examples

[[cron-example-daily]]
===== Setting daily triggers

`0 5 9 * * ?`::
Trigger at 9:05 a.m. UTC every day.

`0 5 9 * * ? 2020`::
Trigger at 9:05 a.m. UTC every day during the year 2020.

[[cron-example-range]]
===== Restricting triggers to a range of days or times

`0 5 9 ? * MON-FRI`::
Trigger at 9:05 a.m. UTC Monday through Friday.

`0 0-5 9 * * ?`::
Trigger every minute starting at 9:00 a.m. UTC and ending at 9:05 a.m. UTC every day.

[[cron-example-interval]]
===== Setting interval triggers

`0 0/15 9 * * ?`::
Trigger every 15 minutes starting at 9:00 a.m. UTC and ending at 9:45 a.m. UTC every day.

`0 5 9 1/3 * ?`::
Trigger at 9:05 a.m. UTC every 3 days every month, starting on the first day of the month.

[[cron-example-day]]
===== Setting schedules that trigger on a particular day

`0 1 4 1 4 ?`::
Trigger every April 1st at 4:01 a.m. UTC.
`0 0,30 9 ? 4 WED`::
Trigger at 9:00 a.m. UTC and at 9:30 a.m. UTC every Wednesday in the month of April.

`0 5 9 15 * ?`::
Trigger at 9:05 a.m. UTC on the 15th day of every month.

`0 5 9 15W * ?`::
Trigger at 9:05 a.m. UTC on the nearest weekday to the 15th of every month.

`0 5 9 ? * 6#1`::
Trigger at 9:05 a.m. UTC on the first Friday of every month.

[[cron-example-last]]
===== Setting triggers using last

`0 5 9 L * ?`::
Trigger at 9:05 a.m. UTC on the last day of every month.

`0 5 9 ? * 2L`::
Trigger at 9:05 a.m. UTC on the last Monday of every month.

`0 5 9 LW * ?`::
Trigger at 9:05 a.m. UTC on the last weekday of every month.
