:plugin: dissect
:type: filter

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[id="plugins-{type}s-{plugin}"]

=== Dissect filter plugin

include::{include_path}/plugin_header.asciidoc[]

==== Description

The Dissect filter plugin tokenizes incoming strings using defined patterns. 
It extracts unstructured event data into fields using
delimiters. This process is called tokenization.

Unlike a regular split operation where one delimiter is applied to the whole
string, the Dissect operation applies a set of delimiters to a string value. 

NOTE: All keys must be found and extracted for tokenization to be successful.
If one or more keys cannot be found, an error occurs and the original event is
not modified.

===== Dissect or Grok? Or both?

Dissect differs from Grok in that it does not use regular expressions and is faster. 
Dissect works well when data is reliably repeated.
Grok is a better choice when the structure of your text varies from line to line.

You can use both Dissect and Grok for a hybrid use case when a section of the
line is reliably repeated, but the entire line is not. The Dissect filter can
deconstruct the section of the line that is repeated. The Grok filter can process
the remaining field values with more regex predictability.

===== Terminology

*dissect pattern* - the set of fields and delimiters describing the textual 
format. Also known as a dissection. 
The dissection is described using a set of `%{}` sections:
`%{a} - %{b} - %{c}`

*field* - the text from `%{` to `}` inclusive.

*delimiter* - the text between `}` and the next `%{` characters.
Any set of characters other than `%{`, `'not }'`, or `}` is a delimiter.

*key* - the text between the `%{` and `}`, exclusive of the `?`, `+`, `&` prefixes 
and the ordinal suffix. 

Examples:

`%{?aaa}` - the key is `aaa` 

`%{+bbb/3}` - the key is `bbb` 

`%{&ccc}` - the key is `ccc` 

NOTE: Using the `.` (dot) as `key` will generate fields with `.` in the field name. If
you want to get nested fields, use the brackets notation such as `%{[fieldname][subfieldname]}`.

===== Sample configuration

The config might look like this:

[source,ruby]
-----
  filter {
    dissect {
      mapping => {
        "message" => "%{ts} %{+ts} %{+ts} %{src} %{} %{prog}[%{pid}]: %{msg}"
      }
    }
  }
-----

When a string is dissected from left to right, text is captured up to the first
delimiter. The captured text is stored in the first field. This is repeated
for each field/# delimiter pair until the last delimiter is reached.
Then *the remaining text is stored in the last field*. 

==== Notations

<<plugins-{type}s-{plugin}-normal>>

<<plugins-{type}s-{plugin}-skip>>

<<plugins-{type}s-{plugin}-append>> 

<<plugins-{type}s-{plugin}-indirect>> 

===== Notes and usage guidelines

* For append or indirect fields, the key can refer to a field that already exists in the event before dissection.

* Use a Skip field if you do not want the indirection key/value stored.
+
Example: 
+
`%{?a}: %{&a}` applied to text `google: 77.98` will build a key/value of `google => 77.98`.

* Append and indirect cannot be combined. 
+
Examples:
+
`%{+&something}` will add a value to the `&something` key (probably not the intended outcome). 
+
`%{&+something}` will add a value to the `+something` key (again probably unintended). 

[id="plugins-{type}s-{plugin}-normal"]
===== Normal field notation
The found value is added to the Event using the key. 
A normal field has no prefix or suffix.

Example:

`%{some_field}`


[id="plugins-{type}s-{plugin}-skip"]
===== Skip field notation
The found value is stored internally, but is not added to the Event. 
The key, if supplied, is prefixed with a `?`.

Examples:

`%{}` is an empty skip field.

`%{?foo}` is a named skip field.

[id="plugins-{type}s-{plugin}-append"]
===== Append field notation
If the value is the first field seen, it is stored. 
Subsequent fields are appended to another value. 

The key is prefixed with a `+`. 
The final value is stored in the Event using the key. 

NOTE: The delimiter found before the field is appended with the value. 
If no delimiter is found before the field, a single space character is used.

Examples:

`%{+some_field}` is an append field. 

`%{+some_field/2}` is an append field with an order modifier.

**Order modifiers**

An order modifier, `/digits`, allows one to reorder the append sequence. 

Example: 

For text `1 2 3 go`, this `%{+a/2} %{+a/1} %{+a/4} %{+a/3}` will build a key/value of `a => 2 1 go 3`. 

*Append fields* without an order modifier will append in declared order. 

Example:

For text `1 2 3 go`, this `%{a} %{b} %{+a}` will build two key/values of `a => 1 3 go, b => 2` 

[id="plugins-{type}s-{plugin}-indirect"]
===== Indirect field notation
The found value is added to the Event using the found value of another field as the key. 
The key is prefixed with a `&`. 

Examples:

`%{&some_field}` is an indirect field where the key is indirectly sourced from the value of `some_field`. 

For text `error: some_error, some_description`, this notation `error: %{?err}, %{&err}` will build a key/value of `some_error => some_description`.



==== Multiple Consecutive Delimiter Handling

IMPORTANT: Multiple found delimiter handling has changed starting with version 1.1.1 of this plugin.
Now multiple consecutive delimiters are seen as missing fields by default and not padding.
If you are already using Dissect and your source text has fields padded with extra delimiters,
you will need to change your config. Please read the section below.


===== Empty data between delimiters

Given this text as the sample used to create a dissection:

[source,ruby]
-----
John Smith,Big Oaks,Wood Lane,Hambledown,Canterbury,CB34RY
-----

The created dissection, with 6 fields, is:

[source,ruby]
-----
%{name},%{addr1},%{addr2},%{addr3},%{city},%{zip}
-----

When a line like this is processed:

[source,ruby]
-----
Jane Doe,4321 Fifth Avenue,,,New York,87432
-----

Dissect will create an event with empty fields for `addr2 and addr3` like so:

[source,ruby]
-----
{
  "name": "Jane Doe",
  "addr1": "4321 Fifth Avenue",
  "addr2": "",
  "addr3": "",
  "city": "New York"
  "zip": "87432"
}
-----

===== Delimiters used as padding to visually align fields
*Padding to the right hand side*

Given these texts as the samples used to create a dissection:

[source,ruby]
-----
00000043 ViewReceive     machine-321
f3000a3b Calc            machine-123
-----

The dissection, with 3 fields, is:

[source,ruby]
-----
%{id} %{function->} %{server}
-----

Note, above, the second field has a `->` suffix which tells Dissect to ignore padding to its right. +
Dissect will create these events:

[source,ruby]
-----
{
  "id": "00000043",
  "function": "ViewReceive",
  "server": "machine-123"
}
{
  "id": "f3000a3b",
  "function": "Calc",
  "server": "machine-321"
}
-----

IMPORTANT: Always add the `->` suffix to the field on the left of the padding.

*Padding to the left hand side (to the human eye)*

Given these texts as the samples used to create a dissection:

[source,ruby]
-----
00000043     ViewReceive machine-321
f3000a3b            Calc machine-123
-----

The dissection, with 3 fields, is now:

[source,ruby]
-----
%{id->} %{function} %{server}
-----

Here the `->` suffix moves to the `id` field because Dissect sees the padding as being to the right of the `id` field. +

==== Conditional processing

You probably want to use this filter inside an `if` block. 
This ensures that the event contains a field value with a suitable structure for the dissection.

Example:

[source,ruby]
-----
filter {
  if [type] == "syslog" or "syslog" in [tags] {
    dissect {
      mapping => {
        "message" => "%{ts} %{+ts} %{+ts} %{src} %{} %{prog}[%{pid}]: %{msg}"
      }
    }
  }
}
-----

[id="plugins-{type}s-{plugin}-options"]
==== Dissect Filter Configuration Options

This plugin supports the following configuration options plus the <<plugins-{type}s-{plugin}-common-options>> described later.

[cols="<,<,<",options="header",]
|=======================================================================
|Setting |Input type|Required
| <<plugins-{type}s-{plugin}-convert_datatype>> |<<hash,hash>>|No
| <<plugins-{type}s-{plugin}-mapping>> |<<hash,hash>>|No
| <<plugins-{type}s-{plugin}-tag_on_failure>> |<<array,array>>|No
|=======================================================================

Also see <<plugins-{type}s-{plugin}-common-options>> for a list of options supported by all
filter plugins.

&nbsp;

[id="plugins-{type}s-{plugin}-convert_datatype"]
===== `convert_datatype`

  * Value type is <<hash,hash>>
  * Default value is `{}`

With this setting `int` and `float` datatype conversions can be specified. 
These will be done after all `mapping` dissections have taken place. 
Feel free to use this setting on its own without a `mapping` section. 

*Example*

[source, ruby]
-----
filter {
  dissect {
    convert_datatype => {
      "cpu" => "float"
      "code" => "int"
    }
  }
}
-----

[id="plugins-{type}s-{plugin}-mapping"]
===== `mapping`

  * Value type is <<hash,hash>>
  * Default value is `{}`

A hash of dissections of `field => value` +
[IMPORTANT]
Don't use an escaped newline `\n` in the value. It will be interpreted as two characters `\` + `n`.
Instead use actual line breaks in the config.
Also use single quotes to define the value if it contains double quotes.

A later dissection can be done on values from a previous dissection or they can be independent.

*Example*

[source, ruby]
-----
filter {
  dissect {
    mapping => {
      # using an actual line break
      "message" => '"%{field1}" "%{field2}"
 "%{description}"'
      "description" => "%{field3} %{field4} %{field5}"
    }
  }
}
-----

This is useful if you want to keep the field `description` but also
dissect it further.

[id="plugins-{type}s-{plugin}-tag_on_failure"]
===== `tag_on_failure`

  * Value type is <<array,array>>
  * Default value is `["_dissectfailure"]`

Append values to the `tags` field when dissection fails



[id="plugins-{type}s-{plugin}-common-options"]
include::{include_path}/{type}.asciidoc[]
