[[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 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.

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


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

To increase security, scripts for languages that are not deemed to be safe by
default can only be specified in 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.script` setting.

The languages which are assumed to be safe by default are: painless,
expressions, and mustache (used for 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]

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.
