[[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>
    "inline" | "id" | "file": "...", <2>
    "params": { ... } <3>
  }
-------------------------------------
<1> The language the script is written in, which defaults to `groovy`.
<2> The script itself which may be specfied as `inline`, `id`, or `file`.
<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
<<search-request-script-fields, scripted field>>:

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

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

[float]
=== Script Parameters

`lang`::

    Specifies the language the script is written in.  Defaults to `groovy` but
    may be set to any of languages listed in <<modules-scripting>>. The
    default language may be changed in the `elasticsearch.yml` config file by
    setting `script.default_lang` to the appropriate language.


`inline`, `id`, `file`::

    Specifies the source of the script.  An `inline` script is specified
    `inline` as in the example above, a stored script with the specified `id`
    is retrieved from the cluster state (see <<modules-scripting-stored-scripts,Stored Scripts>>),
    and a `file` script is retrieved from a file in the `config/scripts`
    directory (see <<modules-scripting-file-scripts, File Scripts>>).
+
While languages like `expression` and `painless` can be used out of the box as
inline or stored scripts, other languages like `groovy` can only be
specified as `file` unless you first adjust the default
<<modules-scripting-security,scripting security settings>>.

`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]
----------------------
  "inline": "doc['my_field'] * 2"
----------------------

Instead, pass it in as a named parameter:

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

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_per_minute`.

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


[float]
[[modules-scripting-file-scripts]]
=== File-based Scripts

To increase security, non-sandboxed languages can only be specified in script
files stored on every node in the cluster.  File scripts must be saved in the
`scripts` directory whose default location depends on whether you use  the
<<zip-targz-layout,`zip`/`tar.gz`>> (`$ES_HOME/config/scripts/`),
<<rpm-layout,RPM>>, or <<deb-layout,Debian>> package.  The default may be
changed with the `path.scripts` setting.

The languages which are assumed to be safe by default are: `painless`,
`expression`, and `mustache` (used for search and query templates).

Any files placed in the `scripts` directory will be compiled automatically
when the node starts up and then <<reload-scripts,every 60 seconds thereafter>>.

The file should be named as follows: `{script-name}.{lang}`.  For instance,
the following example creates a Groovy script called `calculate-score`:

[source,sh]
--------------------------------------------------
cat "log(_score * 2) + my_modifier" > config/scripts/calculate-score.groovy
--------------------------------------------------

This script can be used as follows:

[source,js]
--------------------------------------------------
GET my_index/_search
{
  "query": {
    "script": {
      "script": {
        "lang":   "groovy", <1>
        "file":   "calculate-score", <2>
        "params": {
          "my_modifier": 2
        }
      }
    }
  }
}
--------------------------------------------------
<1> The language of the script, which should correspond with the script file suffix.
<2> The name of the script, which should be the name of the file.

The `script` directory may contain sub-directories, in which case the
hierarchy of directories is flattened and concatenated with underscores.  A
script in `group1/group2/my_script.groovy` should use `group1_group2_myscript`
as the `file` name.


[[reload-scripts]]
[float]
==== Automatic script reloading

The `scripts` directory will be rescanned every `60s` (configurable with the
`resource.reload.interval` setting) and new, changed, or removed scripts will
be compiled, updated, or deleted from the script cache.

Script reloading can be completely disabled by setting
`script.auto_reload_enabled` to `false`.

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

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

[source,js]
-----------------------------------
/_scripts/{lang}/{id} <1> <2>
-----------------------------------
<1> The `lang` represents the script language.
<2> The `id` is a unique identifier or script name.

This example stores a Groovy script called `calculate-score` in the cluster
state:

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

This same script can be retrieved with:

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

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

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

And deleted with:

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

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

All scripts are cached by default so that they only need to be recompiled
when updates occur. File scripts keep a static cache and will always reside
in memory. Both inline and stored scripts are stored in a cache that can evict
residing scripts. 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 stored 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 alternatives like
<<modules-scripting-native,native>> scripts should be considered instead.
