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[DOCS] Create a new page for dissect content in scripting docs (#73437)
* [DOCS] Create a new page for dissect in scripting docs * Expanding a bit more * Adding a section for using dissect patterns * Adding tests * Fix test cases and other edits
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‎docs/reference/scripting/common-script-uses.asciidoc

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@@ -17,15 +17,10 @@ There are two options at your disposal:
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* <<grok,Grok>> is a regular expression dialect that supports aliased
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expressions that you can reuse. Because Grok sits on top of regular expressions
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(regex), any regular expressions are valid in grok as well.
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* <<dissect-processor,Dissect>> extracts structured fields out of text, using
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* <<dissect,Dissect>> extracts structured fields out of text, using
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delimiters to define the matching pattern. Unlike grok, dissect doesn't use regular
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expressions.
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Regex is incredibly powerful but can be complicated. If you don't need the
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power of regular expressions, use dissect patterns, which are simple and
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often faster than grok patterns. Paying special attention to the parts of the string
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you want to discard will help build successful dissect patterns.
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Let's start with a simple example by adding the `@timestamp` and `message`
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fields to the `my-index` mapping as indexed fields. To remain flexible, use
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`wildcard` as the field type for `message`:

‎docs/reference/scripting/dissect-syntax.asciidoc

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[[dissect]]
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=== Dissecting data
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Dissect matches a single text field against a defined pattern. A dissect
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pattern is defined by the parts of the string you want to discard. Paying
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special attention to each part of a string helps to build successful dissect
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patterns.
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If you don't need the power of regular expressions, use dissect patterns instead
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of grok. Dissect uses a much simpler syntax than grok and is typically faster
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overall. The syntax for dissect is transparent: tell dissect what you want and
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it will return those results to you.
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[[dissect-syntax]]
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==== Dissect patterns
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Dissect patterns are comprised of _variables_ and _separators_. Anything
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defined by a percent sign and curly braces `%{}` is considered a variable,
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such as `%{clientip}`. You can assign variables to any part of data in a field,
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and then return only the parts that you want. Separators are any values between
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variables, which could be spaces, dashes, or other delimiters.
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For example, let's say you have log data with a `message` field that looks like
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this:
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[source,js]
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----
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"message" : "247.37.0.0 - - [30/Apr/2020:14:31:22 -0500] \"GET /images/hm_nbg.jpg HTTP/1.0\" 304 0"
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----
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// NOTCONSOLE
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You assign variables to each part of the data to construct a successful
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dissect pattern. Remember, tell dissect _exactly_ what you want you want to
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match on.
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The first part of the data looks like an IP address, so you
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can assign a variable like `%{clientip}`. The next two characters are dashes
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with a space on either side. You can assign a variable for each dash, or a
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single variable to represent the dashes and spaces. Next are a set of brackets
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containing a timestamp. The brackets are a separator, so you include those in
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the dissect pattern. Thus far, the data and matching dissect pattern look like
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this:
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[source,js]
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----
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247.37.0.0 - - [30/Apr/2020:14:31:22 -0500] <1>
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%{clientip} %{ident} %{auth} [%{@timestamp}] <2>
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----
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// NOTCONSOLE
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<1> The first chunks of data from the `message` field
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<2> Dissect pattern to match on the selected data chunks
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Using that same logic, you can create variables for the remaining chunks of
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data. Double quotation marks are separators, so include those in your dissect
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pattern. The pattern replaces `GET` with a `%{verb}` variable, but keeps `HTTP`
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as part of the pattern.
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[source,js]
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----
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\"GET /images/hm_nbg.jpg HTTP/1.0\" 304 0
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"%{verb} %{request} HTTP/%{httpversion}" %{response} %{size}
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----
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// NOTCONSOLE
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Combining the two patterns results in a dissect pattern that looks like this:
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[source,js]
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----
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%{clientip} %{ident} %{auth} [%{@timestamp}] \"%{verb} %{request} HTTP/%{httpversion}\" %{status} %{size}
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----
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// NOTCONSOLE
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Now that you have a dissect pattern, how do you test and use it?
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[[dissect-patterns-test]]
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==== Test dissect patterns with Painless
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You can incorporate dissect patterns into Painless scripts to extract
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data. To test your script, use either the {painless}/painless-execute-api.html#painless-execute-runtime-field-context[field contexts] of the Painless
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execute API or create a runtime field that includes the script. Runtime fields
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offer greater flexibility and accept multiple documents, but the Painless execute
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API is a great option if you don't have write access on a cluster where you're
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testing a script.
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For example, test your dissect pattern with the Painless execute API by
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including your Painless script and a single document that matches your data.
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Start by indexing the `message` field as a `wildcard` data type:
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[source,console]
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----
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PUT my-index
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{
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"mappings": {
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"properties": {
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"message": {
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"type": "wildcard"
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}
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}
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}
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}
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----
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If you want to retrieve the HTTP response code, add your dissect pattern to a
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Painless script that extracts the `response` value. To extract values from a
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field, use this function:
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[source,painless]
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----
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`.extract(doc["<field_name>"].value)?.<field_value>`
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----
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In this example, `message` is the `<field_name>` and `response` is the
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`<field_value>`:
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[source,console]
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----
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POST /_scripts/painless/_execute
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{
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"script": {
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"source": """
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String response=dissect('%{clientip} %{ident} %{auth} [%{@timestamp}] "%{verb} %{request} HTTP/%{httpversion}" %{response} %{size}').extract(doc["message"].value)?.response;
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if (response != null) emit(Integer.parseInt(response)); <1>
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"""
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},
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"context": "long_field", <2>
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"context_setup": {
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"index": "my-index",
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"document": { <3>
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"message": """247.37.0.0 - - [30/Apr/2020:14:31:22 -0500] "GET /images/hm_nbg.jpg HTTP/1.0" 304 0"""
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}
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}
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}
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----
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// TEST[continued]
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<1> Runtime fields require the `emit` method to return values.
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<2> Because the response code is an integer, use the `long_field` context.
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<3> Include a sample document that matches your data.
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The result includes the HTTP response code:
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[source,console-result]
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----
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{
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"result" : [
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304
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]
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}
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----
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[[dissect-patterns-runtime]]
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==== Use dissect patterns and scripts in runtime fields
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If you have a functional dissect pattern, you can add it to a runtime field to
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manipulate data. Because runtime fields don't require you to index fields, you
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have incredible flexibility to modify your script and how it functions. If you
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already <<dissect-patterns-test,tested your dissect pattern>> using the Painless
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execute API, you can use that _exact_ Painless script in your runtime field.
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To start, add the `message` field as a `wildcard` type like in the previous
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section, but also add `@timestamp` as a `date` in case you want to operate on
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that field for <<common-script-uses,other use cases>>:
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[source,console]
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----
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PUT /my-index/
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{
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"mappings": {
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"properties": {
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"@timestamp": {
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"format": "strict_date_optional_time||epoch_second",
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"type": "date"
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},
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"message": {
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"type": "wildcard"
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}
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}
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}
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}
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----
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If you want to extract the HTTP response code using your dissect pattern, you
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can create a runtime field like `http.response`:
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[source,console]
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----
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PUT my-index/_mappings
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{
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"runtime": {
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"http.response": {
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"type": "long",
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"script": """
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String response=dissect('%{clientip} %{ident} %{auth} [%{@timestamp}] "%{verb} %{request} HTTP/%{httpversion}" %{response} %{size}').extract(doc["message"].value)?.response;
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if (response != null) emit(Integer.parseInt(response));
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"""
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}
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}
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}
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----
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// TEST[continued]
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After mapping the fields you want to retrieve, index a few records from
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your log data into {es}. The following request uses the <<docs-bulk,bulk API>>
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to index raw log data into `my-index`:
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[source,console]
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----
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POST /my-index/_bulk?refresh=true
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{"index":{}}
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{"timestamp":"2020-04-30T14:30:17-05:00","message":"40.135.0.0 - - [30/Apr/2020:14:30:17 -0500] \"GET /images/hm_bg.jpg HTTP/1.0\" 200 24736"}
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{"index":{}}
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{"timestamp":"2020-04-30T14:30:53-05:00","message":"232.0.0.0 - - [30/Apr/2020:14:30:53 -0500] \"GET /images/hm_bg.jpg HTTP/1.0\" 200 24736"}
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{"index":{}}
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{"timestamp":"2020-04-30T14:31:12-05:00","message":"26.1.0.0 - - [30/Apr/2020:14:31:12 -0500] \"GET /images/hm_bg.jpg HTTP/1.0\" 200 24736"}
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{"index":{}}
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{"timestamp":"2020-04-30T14:31:19-05:00","message":"247.37.0.0 - - [30/Apr/2020:14:31:19 -0500] \"GET /french/splash_inet.html HTTP/1.0\" 200 3781"}
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{"index":{}}
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{"timestamp":"2020-04-30T14:31:22-05:00","message":"247.37.0.0 - - [30/Apr/2020:14:31:22 -0500] \"GET /images/hm_nbg.jpg HTTP/1.0\" 304 0"}
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{"index":{}}
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{"timestamp":"2020-04-30T14:31:27-05:00","message":"252.0.0.0 - - [30/Apr/2020:14:31:27 -0500] \"GET /images/hm_bg.jpg HTTP/1.0\" 200 24736"}
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{"index":{}}
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{"timestamp":"2020-04-30T14:31:28-05:00","message":"not a valid apache log"}
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----
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// TEST[continued]
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You can define a simple query to run a search for a specific HTTP response and
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return all related fields. Use the `fields` parameter of the search API to
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retrieve the `http.response` runtime field.
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[source,console]
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----
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GET my-index/_search
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{
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"query": {
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"match": {
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"http.response": "304"
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}
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},
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"fields" : ["http.response"]
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}
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----
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// TEST[continued]
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Alternatively, you can define the same runtime field but in the context of a
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search request. The runtime definition and the script are exactly the same as
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the one defined previously in the index mapping. Just copy that definition into
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the search request under the `runtime_mappings` section and include a query
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that matches on the runtime field. This query returns the same results as the
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search query previously defined for the `http.response` runtime field in your
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index mappings, but only in the context of this specific search:
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[source,console]
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----
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GET my-index/_search
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{
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"runtime_mappings": {
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"http.response": {
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"type": "long",
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"script": """
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String response=dissect('%{clientip} %{ident} %{auth} [%{@timestamp}] "%{verb} %{request} HTTP/%{httpversion}" %{response} %{size}').extract(doc["message"].value)?.response;
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if (response != null) emit(Integer.parseInt(response));
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"""
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}
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},
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"query": {
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"match": {
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"http.response": "304"
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}
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},
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"fields" : ["http.response"]
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}
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----
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// TEST[continued]
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// TEST[s/_search/_search\?filter_path=hits/]
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[source,console-result]
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----
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{
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"hits" : {
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"total" : {
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"value" : 1,
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"relation" : "eq"
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},
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"max_score" : 1.0,
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"hits" : [
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{
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"_index" : "my-index",
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"_id" : "D47UqXkBByC8cgZrkbOm",
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"_score" : 1.0,
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"_source" : {
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"timestamp" : "2020-04-30T14:31:22-05:00",
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"message" : "247.37.0.0 - - [30/Apr/2020:14:31:22 -0500] \"GET /images/hm_nbg.jpg HTTP/1.0\" 304 0"
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},
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"fields" : {
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"http.response" : [
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304
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]
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}
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}
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]
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}
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}
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----
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// TESTRESPONSE[s/"_id" : "D47UqXkBByC8cgZrkbOm"/"_id": $body.hits.hits.0._id/]

‎docs/reference/scripting/using.asciidoc

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////
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include::dissect-syntax.asciidoc[]
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include::grok-syntax.asciidoc[]

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