# Standard input The *Standard input* plugin supports retrieving a message stream from the standard input interface (`stdin`) of the Fluent Bit process. To use it, specify the plugin name as the input. For example: ```shell fluent-bit -i stdin -o stdout ``` If the `stdin` stream is closed (`end-of-file`), the plugin instructs Fluent Bit to exit with success (`0`) after flushing any pending output. ## Configuration parameters The plugin supports the following configuration parameters: | Key | Description | Default | | ------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ------- | | `Buffer_Size` | Set the buffer size to read data. This value is used to increase buffer size and must be set according to the [Unit Size](/manual/4.0/administration/configuring-fluent-bit/unit-sizes.md) specification. | `16k` | | `Parser` | The name of the parser to invoke instead of the default JSON input parser. | *none* | | `Threaded` | Indicates whether to run this input in its own [thread](/manual/4.0/administration/multithreading.md#inputs). | `false` | ## Input formats If no parser is configured for the `stdin` plugin, it expects valid JSON input data in one of the following formats: * A JSON object with one or more key-value pairs: `{ "key": "value", "key2": "value2" }` * A 2-element JSON array in [Fluent Bit Event](/manual/4.0/concepts/key-concepts.md#event-or-record) format, which can be: * `[TIMESTAMP, { "key": "value" }]` where TIMESTAMP is a floating point value representing a timestamp in seconds. * From Fluent Bit v2.1.0, `[[TIMESTAMP, METADATA], { "key": "value" }]` where *`TIMESTAMP`* has the same meaning as previous and *`METADATA`* is a JSON object. Multi-line input JSON is supported. Any input data which isn't in one of the supported formats will cause the plugin to log errors like: ``` [debug] [input:stdin:stdin.0] invalid JSON message, skipping [error] [input:stdin:stdin.0] invalid record found, it's not a JSON map or array ``` To handle inputs in other formats, a parser must be explicitly specified in the configuration for the `stdin` plugin. See [parser input example](#parser-input) for sample configuration. ## Log event timestamps The Fluent Bit event timestamp will be set from the input record if the two-element event input is used or a custom parser configuration supplies a timestamp. Otherwise, the event timestamp will be set to the timestamp at which the record is read by the `stdin` plugin. ## Examples ### JSON input To demonstrate how the plugin works, you can use a `bash` script that generates messages and writes them to [Fluent Bit](http://fluentbit.io). 1. Write the following content in a file named `test.sh`: ```bash #!/bin/sh for ((i=0; i<=5; i++)); do echo -n "{\"key\": \"some value\"}" sleep 1 done ``` 2. Start the script and [Fluent Bit](http://fluentbit.io): ```shell bash test.sh | fluent-bit -q -i stdin -o stdout ``` 3. The command should return output like the following: ``` [0] stdin.0: [[1684196745.942883835, {}], {"key"=>"some value"}] [0] stdin.0: [[1684196746.938949056, {}], {"key"=>"some value"}] [0] stdin.0: [[1684196747.940162493, {}], {"key"=>"some value"}] [0] stdin.0: [[1684196748.941392297, {}], {"key"=>"some value"}] [0] stdin.0: [[1684196749.942644238, {}], {"key"=>"some value"}] [0] stdin.0: [[1684196750.943721442, {}], {"key"=>"some value"}] ``` ### JSON input with timestamp 1. An input event timestamp can also be supplied. Replace `test.sh` with: ```bash #!/bin/sh for ((i=0; i<=5; i++)); do echo -n " [ $(date '+%s.%N' -d '1 day ago'), { \"realtimestamp\": $(date '+%s.%N') } ] " sleep 1 done ``` 2. Re-run the sample command. Timestamps output by Fluent Bit are now one day old because Fluent Bit used the input message timestamp. ```shell bash test.sh | fluent-bit -q -i stdin -o stdout ``` 3. Which returns the following: ``` [0] stdin.0: [[1684110480.028171300, {}], {"realtimestamp"=>1684196880.030070}] [0] stdin.0: [[1684110481.033753395, {}], {"realtimestamp"=>1684196881.034741}] [0] stdin.0: [[1684110482.036730051, {}], {"realtimestamp"=>1684196882.037704}] [0] stdin.0: [[1684110483.039903879, {}], {"realtimestamp"=>1684196883.041081}] [0] stdin.0: [[1684110484.044719457, {}], {"realtimestamp"=>1684196884.046404}] [0] stdin.0: [[1684110485.048710107, {}], {"realtimestamp"=>1684196885.049651}] ``` ### JSON input with metadata 1. Additional metadata is supported in Fluent Bit v2.1.0 and later by replacing the timestamp with a two-element object. For example: ```bash #!/bin/sh for ((i=0; i<=5; i++)); do echo -n " [ [ $(date '+%s.%N' -d '1 day ago'), {\"metakey\": \"metavalue\"} ], { \"realtimestamp\": $(date '+%s.%N') } ] " sleep 1 done ``` 2. Run test using the command: ```shell bash ./test.sh | fluent-bit -q -i stdin -o stdout ``` 3. Which returns results like the following: ``` [0] stdin.0: [[1684110513.060139417, {"metakey"=>"metavalue"}], {"realtimestamp"=>1684196913.061017}] [0] stdin.0: [[1684110514.063085317, {"metakey"=>"metavalue"}], {"realtimestamp"=>1684196914.064145}] [0] stdin.0: [[1684110515.066210508, {"metakey"=>"metavalue"}], {"realtimestamp"=>1684196915.067155}] [0] stdin.0: [[1684110516.069149971, {"metakey"=>"metavalue"}], {"realtimestamp"=>1684196916.070132}] [0] stdin.0: [[1684110517.072484016, {"metakey"=>"metavalue"}], {"realtimestamp"=>1684196917.073636}] [0] stdin.0: [[1684110518.075428724, {"metakey"=>"metavalue"}], {"realtimestamp"=>1684196918.076292}] ``` 4. On older Fluent Bit versions records in this format will be discarded. If the log level permits, Fluent Bit will log: ``` [ warn] unknown time format 6 ``` ### Parser input To capture inputs in other formats, specify a parser configuration for the `stdin` plugin. For example, if you want to read raw messages line by line and forward them, you could use a separate parsers file that captures the whole message line: {% tabs %} {% tab title="parsers.yaml" %} ```yaml parsers: - name: stringify_message format: regex key_name: message regex: '^(?.*)' ``` {% endtab %} {% tab title="parsers.conf" %} ``` [PARSER] name stringify_message format regex Key_Name message regex ^(?.*) ``` {% endtab %} {% endtabs %} You can then use the parsers file in a `stdin` plugin in the main Fluent Bit configuration file as follows: {% tabs %} {% tab title="fluent-bit.yaml" %} ```yaml service: parsers_file: parsers.yaml pipeline: inputs: - name: stdin tag: stdin parser: stringify_message outputs: - name: stdout match: '*' ``` {% endtab %} {% tab title="fluent-bit.conf" %} ``` [SERVICE] parsers_file parsers.conf [INPUT] Name stdin Tag stdin Parser stringify_message [OUTPUT] Name stdout Match * ``` {% endtab %} {% endtabs %} Fluent Bit will now read each line and emit a single message for each input line, using the following command: ```shell # For YAML configuration. seq 1 5 | ./fluent-bit --config fluent-bit.yaml # For classic configuration. seq 1 5 | ./fluent-bit --config fluent-bit.conf ``` Which returns output similar to: ``` ... [0] stdin: [[1751545974.960182000, {}], {"message"=>"1"}] [1] stdin: [[1751545974.960246000, {}], {"message"=>"2"}] [2] stdin: [[1751545974.960255000, {}], {"message"=>"3"}] [3] stdin: [[1751545974.960262000, {}], {"message"=>"4"}] [4] stdin: [[1751545974.960268000, {}], {"message"=>"5"}] ... ``` In production deployments it's best to use a parser that splits messages into real fields and adds appropriate tags. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.fluentbit.io/manual/4.0/data-pipeline/inputs/standard-input.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.