# parser

The `filter_parser` filter plugin "parses" string field in event records and mutates its event record with parsed result.

## Example Configurations

`filter_parser` is included in Fluentd's core since v0.12.29. No installation required. If you want to use `filter_parser` with lower fluentd versions, need to install `fluent-plugin-parser`.

`filter_parser` has just same with `in_tail` about `format` and `time_format`:

```
<filter foo.bar>
  @type parser
  format /^(?<host>[^ ]*) [^ ]* (?<user>[^ ]*) \[(?<time>[^\]]*)\] "(?<method>\S+)(?: +(?<path>[^ ]*) +\S*)?" (?<code>[^ ]*) (?<size>[^ ]*)$/
  time_format %d/%b/%Y:%H:%M:%S %z
  key_name message
</filter>
```

`filter_parser` uses built-in parser plugins and your own customized parser plugin, so you can re-use pre-defined format like `apache`, `json` and etc. See document page for more details: [Parser Plugin Overview](/0.12/parser.md)

## Parameters

### format

This is required parameter. Specify parser format or regexp pattern.

### key\_name

This is required parameter. Specify field name in the record to parse.

### reserve\_data

Keep original key-value pair in parsed result. Default is `false`.

```
<filter foo.bar>
  @type parser
  format json
  key_name log
  reserve_data true
</filter>
```

With above configuration, result is below:

```
# input data:  {"key":"value","log":"{\"user\":1,\"num\":2}"}
# output data: {"key":"value","log":"{\"user\":1,\"num\":2}","user":1,"num":2}
```

Without `reserve_data`, result is below

```
# input data:  {"key":"value","log":"{\"user\":1,\"num\":2}"}
# output data: {"user":1,"num":2}
```

### suppress\_parse\_error\_log

If `true`, a plugin suppresses `pattern not match` warning log. Default is `false`.

This parameter is useful for parsing mixed logs and you want to ignore non target lines.

### ignore\_key\_not\_exist

Ignore "key not exist" log. Default is `false`.

Useful case is same with `suppress_parse_error_log`.

### replace\_invalid\_sequence

If `true`, invalid string is replaced with safe characters and re-parse it. Default is `false`.

### inject\_key\_prefix

Store parsed values with specified key name prefix. Default is `nil`.

```
<filter foo.bar>
  @type parser
  format json
  key_name log
  reserve_data true
  inject_key_prefix data.
</filter>
```

With above configuration, result is below:

```
# input data:  {"log": "{\"user\":1,\"num\":2}"}
# output data: {"log":"{\"user\":1,\"num\":2}","data.user":1, "data.num":2}
```

### hash\_value\_field

Store parsed values as a hash value in a field. Default is `nil`.

```
<filter foo.bar>
  @type parser
  format json
  key_name log
  hash_value_field parsed
</filter>
```

With above configuration, result is below:

```
# input data:  {"log": "{\"user\":1,\"num\":2}"}
# output data: {"parsed":{"user":1,"num":2}}
```

### time\_parse

If false, time parsing is disabled in the parser. Default is true.

### emit\_invalid\_record\_to\_error

Emit invalid record to `@ERROR` label. Default is `false`. Invalid cases are

* key not exist
* format is not matched
* unexpected error

You can rescue unexpected format logs in `@ERROR` label.

## Learn More

* [Filter Plugin Overview](/0.12/filter.md)

If this article is incorrect or outdated, or omits critical information, please [let us know](https://github.com/fluent/fluentd-docs-gitbook/issues?state=open). [Fluentd](http://www.fluentd.org/) is a open source project under [Cloud Native Computing Foundation (CNCF)](https://cncf.io/). All components are available under the Apache 2 License.


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