Dissect filter plugin

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.

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

The config might look like this:

  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.

The found value is added to the Event using the key. A normal field has no prefix or suffix.

Example:

%{some_field}

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.

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.

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

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.

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

John Smith,Big Oaks,Wood Lane,Hambledown,Canterbury,CB34RY

The created dissection, with 6 fields, is:

%{name},%{addr1},%{addr2},%{addr3},%{city},%{zip}

When a line like this is processed:

Jane Doe,4321 Fifth Avenue,,,New York,87432

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

{
  "name": "Jane Doe",
  "addr1": "4321 Fifth Avenue",
  "addr2": "",
  "addr3": "",
  "city": "New York"
  "zip": "87432"
}

Padding to the right hand side

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

00000043 ViewReceive     machine-321
f3000a3b Calc            machine-123

The dissection, with 3 fields, is:

%{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:

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

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

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

00000043     ViewReceive machine-321
f3000a3b            Calc machine-123

The dissection, with 3 fields, is now:

%{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.

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

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

A hash of dissections of field => value

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

Example

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.

Append values to the tags field when dissection fails

If this filter is successful, add any arbitrary fields to this event. Field names can be dynamic and include parts of the event using the %{field}.

Example:

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

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

If the event has field "somefield" == "hello" this filter, on success, would add field foo_hello if it is present, with the value above and the %{host} piece replaced with that value from the event. The second example would also add a hardcoded field.

If this filter is successful, add arbitrary tags to the event. Tags can be dynamic and include parts of the event using the %{field} syntax.

Example:

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

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

If the event has field "somefield" == "hello" this filter, on success, would add a tag foo_hello (and the second example would of course add a taggedy_tag tag).

Disable or enable metric logging for this specific plugin instance. By default we record all the metrics we can, but you can disable metrics collection for a specific plugin.

Add a unique ID to the plugin configuration. If no ID is specified, Logstash will generate one. It is strongly recommended to set this ID in your configuration. This is particularly useful when you have two or more plugins of the same type, for example, if you have 2 dissect filters. Adding a named ID in this case will help in monitoring Logstash when using the monitoring APIs.

    filter {
      dissect {
        id => "ABC"
      }
    }

Call the filter flush method at regular interval. Optional.

If this filter is successful, remove arbitrary fields from this event. Fields names can be dynamic and include parts of the event using the %{field} Example:

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

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

If the event has field "somefield" == "hello" this filter, on success, would remove the field with name foo_hello if it is present. The second example would remove an additional, non-dynamic field.

If this filter is successful, remove arbitrary tags from the event. Tags can be dynamic and include parts of the event using the %{field} syntax.

Example:

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

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

If the event has field "somefield" == "hello" this filter, on success, would remove the tag foo_hello if it is present. The second example would remove a sad, unwanted tag as well.