Write your first script

Painless is the default scripting language for Elasticsearch. It is secure, performant, and provides a natural syntax for anyone with a little coding experience.

A Painless script is structured as one or more statements and optionally has one or more user-defined functions at the beginning. A script must always have at least one statement.

The Painless execute API provides the ability to test a script with simple user-defined parameters and receive a result. Let’s start with a complete script and review its constituent parts.

1. Index a document

   Index a document with a single field so that we have some data to work with:

   PUT my-index-000001/_doc/1
   {
     "my_field": 5
   }

2. Operate on a field

   You can now construct a script that operates on that field and then evaluate the script as part of a query. The following query uses the script_fields parameter of the search API to retrieve a script valuation.

   The components of this script are detailed in later pages. For now, note that the script takes my_field as input and operates on it.

   GET my-index-000001/_search
   {
     "script_fields": {
       "my_doubled_field": {
         "script": {
           "source": "doc['my_field'].value * params['multiplier']",
           "params": {
             "multiplier": 2
           }
         }
       }
     }
   }

   1. script object
   2. script source

   The script is a standard JSON object that defines scripts under most APIs in Elasticsearch. This object requires source to define the script itself. Since script isn't set, the scripting language is interpreted as being Painless, by default.