[[schedule-cron]]
==== Cron schedule

Defines a <<trigger-schedule, `schedule`>> using a <<cron-expressions, cron expression>> 
that specifiues when to execute a watch.

TIP:  While cron expressions are powerful, a regularly occurring schedule 
is easier to configure with the other schedule types. 
If you must use a cron schedule, make sure you verify it with 
<<elasticsearch-croneval, `elasticsearch-croneval`>> . 


===== Configure a cron schedule with one time

To configure a `cron` schedule, you simply specify the cron expression as a
string value. For example, the following snippet configures a `cron` schedule
that triggers every day at noon:

[source,js]
--------------------------------------------------
{
  ...
  "trigger" : {
    "schedule" : {
      "cron" : "0 0 12 * * ?"
    }
  }
  ...
}
--------------------------------------------------
// NOTCONSOLE

[[_configuring_a_multiple_times_cron_schedule]]
===== Configure a cron schedule with multiple times

To configure a `cron` schedule that triggers multiple times, you can
specify an array of cron expressions. For example, the following `cron`
schedule triggers every even minute during weekdays and every uneven
minute during the weekend:

[source,js]
--------------------------------------------------
{
  ...
  "trigger" : {
    "schedule" : {
      "cron" : [
        "0 0/2 * ? * MON-FRI"",
        "0 1-59/2 * ? * SAT-SUN"
      ]
    }
  }
  ...
}
--------------------------------------------------
// NOTCONSOLE

[[croneval]]
===== Use croneval to validate cron expressions

{es} provides a <<elasticsearch-croneval, `elasticsearch-croneval`>> command line tool 
in the `$ES_HOME/bin` directory that you can use to check that your cron expressions 
are valid and produce the expected results.

To validate a cron expression, pass it in as a parameter to `elasticsearch-croneval`:	

[source,bash]
--------------------------------------------------
bin/elasticsearch-croneval "0 0/1 * * * ?"
--------------------------------------------------