[[modules-scripting-using]]
== How to use scripts

Wherever scripting is supported in the Elasticsearch API, the syntax follows
the same pattern:

[source,js]
-------------------------------------
  "script": {
    "lang":   "...",  <1>
    "source" | "id": "...", <2>
    "params": { ... } <3>
  }
-------------------------------------
// NOTCONSOLE
<1> The language the script is written in, which defaults to `painless`.
<2> The script itself which may be specified as `source` for an inline script or `id` for a stored script.
<3> Any named parameters that should be passed into the script.

For example, the following script is used in a search request to return a
<<request-body-search-script-fields, scripted field>>:

[source,js]
-------------------------------------
PUT my_index/_doc/1
{
  "my_field": 5
}

GET my_index/_search
{
  "script_fields": {
    "my_doubled_field": {
      "script": {
        "lang":   "expression",
        "source": "doc['my_field'] * multiplier",
        "params": {
          "multiplier": 2
        }
      }
    }
  }
}
-------------------------------------
// CONSOLE

[float]
=== Script parameters

`lang`::

    Specifies the language the script is written in.  Defaults to `painless`.


`source`, `id`::

    Specifies the source of the script.  An `inline` script is specified
    `source` as in the example above. A `stored` script is specified `id`
    and is retrieved from the cluster state (see <<modules-scripting-stored-scripts,Stored Scripts>>).


`params`::

    Specifies any named parameters that are passed into the script as
    variables.

[IMPORTANT]
[[prefer-params]]
.Prefer parameters
========================================

The first time Elasticsearch sees a new script, it compiles it and stores the
compiled version in a cache. Compilation can be a heavy process.

If you need to pass variables into the script, you should pass them in as
named `params` instead of hard-coding values into the script itself.  For
example, if you want to be able to multiply a field value by different
multipliers, don't hard-code the multiplier into the script:

[source,js]
----------------------
  "source": "doc['my_field'] * 2"
----------------------
// NOTCONSOLE

Instead, pass it in as a named parameter:

[source,js]
----------------------
  "source": "doc['my_field'] * multiplier",
  "params": {
    "multiplier": 2
  }
----------------------
// NOTCONSOLE

The first version has to be recompiled every time the multiplier changes.  The
second version is only compiled once.

If you compile too many unique scripts within a small amount of time,
Elasticsearch will reject the new dynamic scripts with a
`circuit_breaking_exception` error. By default, up to 15 inline scripts per
minute will be compiled. You can change this setting dynamically by setting
`script.max_compilations_rate`.

========================================

[float]
[[modules-scripting-short-script-form]]
=== Short script form
A short script form can be used for brevity. In the short form, `script` is represented
by a string instead of an object. This string contains the source of the script.

Short form:

[source,js]
----------------------
  "script": "ctx._source.likes++"
----------------------
// NOTCONSOLE

The same script in the normal form:

[source,js]
----------------------
  "script": {
    "source": "ctx._source.likes++"
  }
----------------------
// NOTCONSOLE

[float]
[[modules-scripting-stored-scripts]]
=== Stored scripts

Scripts may be stored in and retrieved from the cluster state using the
`_scripts` end-point.

[float]
==== Request examples

The following are examples of using a stored script that lives at
`/_scripts/{id}`.

First, create the script called `calculate-score` in the cluster state:

[source,js]
-----------------------------------
POST _scripts/calculate-score
{
  "script": {
    "lang": "painless",
    "source": "Math.log(_score * 2) + params.my_modifier"
  }
}
-----------------------------------
// CONSOLE

This same script can be retrieved with:

[source,js]
-----------------------------------
GET _scripts/calculate-score
-----------------------------------
// CONSOLE
// TEST[continued]

Stored scripts can be used by specifying the `id` parameters as follows:

[source,js]
--------------------------------------------------
GET _search
{
  "query": {
    "script": {
      "script": {
        "id": "calculate-score",
        "params": {
          "my_modifier": 2
        }
      }
    }
  }
}
--------------------------------------------------
// CONSOLE
// TEST[continued]

And deleted with:

[source,js]
-----------------------------------
DELETE _scripts/calculate-score
-----------------------------------
// CONSOLE
// TEST[continued]

[float]
[[modules-scripting-search-templates]]
=== Search templates
You can also use the `_scripts` API to store **search templates**. Search
templates save specific <<search-search,search requests>> with placeholder
values, called template parameters.

You can use stored search templates to run searches without writing out the
entire query. Just provide the stored template's ID and the template parameters.
This is useful when you want to run a commonly used query quickly and without
mistakes.

Search templates use the http://mustache.github.io/mustache.5.html[mustache
templating language]. See <<search-template>> for more information and examples.

[float]
[[modules-scripting-using-caching]]
=== Script caching

All scripts are cached by default so that they only need to be recompiled
when updates occur. By default, scripts do not have a time-based expiration, but
you can change this behavior by using the `script.cache.expire` setting.
You can configure the size of this cache by using the `script.cache.max_size` setting.
By default, the cache size is `100`.

NOTE: The size of scripts is limited to 65,535 bytes. This can be
changed by setting `script.max_size_in_bytes` setting to increase that soft
limit, but if scripts are really large then a
<<modules-scripting-engine,native script engine>> should be considered.