Dissect filter plugin

For questions about the plugin, open a topic in the Discuss forums. For bugs or feature requests, open an issue in Github. For the list of Elastic supported plugins, please consult the Elastic Support Matrix.

The Dissect filter is a kind of split operation. Unlike a regular split operation where one delimiter is applied to the whole string, this operation applies a set of delimiters # to a string value.
Dissect does not use regular expressions and is very fast.
However, if the structure of your text varies from line to line then Grok is more suitable.
There is a hybrid case where Dissect can be used to de-structure the section of the line that is reliably repeated and then Grok can be used on the remaining field values with # more regex predictability and less overall work to do.

A set of fields and delimiters is called a dissection.

The dissection is described using a set of %{} sections:

%{a} - %{b} - %{c}

A field is the text from % to } inclusive.

A delimiter is the text between } and % characters.

The config might look like this:

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

When dissecting a string from left to right, text is captured upto the first delimiter - this captured text is stored in the first field. This is repeated for each field/# delimiter pair thereafter until the last delimiter is reached, then the remaining text is stored in the last field.

The Key:
The key is the text between the %{ and }, exclusive of the ?, +, & prefixes and the ordinal suffix.
%{?aaa} - key is aaa
%{+bbb/3} - key is bbb
%{&ccc} - key is ccc

Normal field notation:
The found value is added to the Event using the key.
%{some_field} - a normal field has no prefix or suffix

Skip field notation:
The found value is stored internally but not added to the Event.
The key, if supplied, is prefixed with a ?.

%{} is an empty skip field.

%{?foo} is a named skip field.

Append field notation:
The value is appended to another value or stored if its the first field seen.
The key is prefixed with a +.
The final value is stored in the Event using the key.

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

An order modifier, /digits, allows one to reorder the append sequence.
e.g. for a text of 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.
e.g. for a text of 1 2 3 go, this %{a} %{b} %{+a} will build two key/values of a => 1 3 go, b => 2

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 &.
%{&some_field} - an indirect field where the key is indirectly sourced from the value of some_field.
e.g. for a text of error: some_error, some_description, this error: %{?err}, %{&err} will build a key/value of some_error => some_description.

e.g. for a text of google: 77.98, this %{?a}: %{&a} will build a key/value of google => 77.98.

Delimiter repetition:
In the source text if a field has variable width padded with delimiters, the padding will be ignored.
e.g. for texts of:

00000043 ViewReceiver  I
000000b3 Peer          I

with a dissection of %{a} %{b} %{c}; the padding is ignored, event.get([c]) -> "I"

For example…​

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

This plugin supports the following configuration options plus the Common Options described later.

Also see Common Options for a list of options supported by all filter plugins.

filter {
  dissect {
    convert_datatype => {
      cpu => "float"
      code => "int"
    }
  }
}

filter {
  dissect {
    mapping => {
      "message" => "%{field1} %{field2} %{description}"
      "description" => "%{field3} %{field4} %{field5}"
    }
  }
}

The following configuration options are supported by all filter plugins:

filter {
  PLUGIN_NAME {
    add_field => { "foo_%{somefield}" => "Hello world, from %{host}" }
  }
}

# You can also add multiple fields at once:
filter {
  PLUGIN_NAME {
    add_field => {
      "foo_%{somefield}" => "Hello world, from %{host}"
      "new_field" => "new_static_value"
    }
  }
}

filter {
  PLUGIN_NAME {
    add_tag => [ "foo_%{somefield}" ]
  }
}

# You can also add multiple tags at once:
filter {
  PLUGIN_NAME {
    add_tag => [ "foo_%{somefield}", "taggedy_tag"]
  }
}

output {
 stdout {
   id => "ABC"
 }
}

filter {
  PLUGIN_NAME {
    remove_field => [ "foo_%{somefield}" ]
  }
}

# You can also remove multiple fields at once:
filter {
  PLUGIN_NAME {
    remove_field => [ "foo_%{somefield}", "my_extraneous_field" ]
  }
}

filter {
  PLUGIN_NAME {
    remove_tag => [ "foo_%{somefield}" ]
  }
}

# You can also remove multiple tags at once:
filter {
  PLUGIN_NAME {
    remove_tag => [ "foo_%{somefield}", "sad_unwanted_tag"]
  }
}