# Output filter plugin for modifying each event record
Adding arbitary field to event record without custmizing existence plugin.
For example, generated event from *in_tail* doesn't contain "hostname" of running machine.
In this case, you can use *record_modifier* to add "hostname" field to event record.
## Installation
Use RubyGems:
gem install fluent-plugin-record-modifier
## Configuration
type record_modifier
tag foo.filtered
gen_host ${hostname}
foo bar
If following record is passed:
```js
{"message":"hello world!"}
```
then you got new record like below:
```js
{"message":"hello world!", "gen_host":"oreore-mac.local", "foo":"bar"}
```
### char_encoding
Fluentd including some plugins treats the logs as a BINARY by default to forward.
But an user sometimes processes the logs depends on their requirements, e.g. handling char encoding correctly.
`char_encoding` parameter is useful for this case.
```conf
type record_modifier
# set UTF-8 encoding information to string.
char_encoding utf-8
# change char encoding from 'UTF-8' to 'EUC-JP'
char_encoding utf-8:euc-jp
```
### remove_keys
The logs include needless record keys in some cases.
You can remove it by using `remove_keys` parameter.
```conf
type record_modifier
# remove key1 and key2 keys from record
remove_keys key1,key2
```
If following record is passed:
```js
{"key1":"hoge", "key2":"foo", "key3":"bar"}
```
then you got new record like below:
```js
{"key3":"bar"}
```
### Mixins
* [SetTagKeyMixin](https://github.com/fluent/fluentd/blob/master/lib/fluent/mixin.rb#L181)
* [fluent-mixin-config-placeholders](https://github.com/tagomoris/fluent-mixin-config-placeholders)
## TODO
* Adding following features if needed
* Use HandleTagNameMixin to keep original tag
* Replace record value
## Copyright