Grep

Select or exclude records using patterns

The Grep Filter plugin lets you match or exclude specific records based on regular expression patterns for values or nested values.

Configuration parameters

The plugin supports the following configuration parameters:

Key	Value Format	Description
Regex	KEY REGEX	Keep records where the content of KEY matches the regular expression.
Exclude	KEY REGEX	Exclude records where the content of KEY matches the regular expression.
Logical_Op	Operation	Specify a logical operator: AND, OR or legacy (default). In legacy mode the behaviour is either AND or OR depending on whether the grep is including (uses AND) or excluding (uses OR). Available from 2.1 or higher.

Record Accessor Enabled

Enable the Record Accessor feature to specify the KEY. Use the record accessor to match values against nested values.

Filter records

To start filtering records, run the filter from the command line or through the configuration file. The following example assumes that you have a file named lines.txt with the following content:

{"log": "aaa"}
{"log": "aab"}
{"log": "bbb"}
{"log": "ccc"}
{"log": "ddd"}
{"log": "eee"}
{"log": "fff"}
{"log": "ggg"}

Command line

When using the command line, pay close attention to quote the regular expressions. Using a configuration file might be easier.

The following command loads the tail plugin and reads the content of lines.txt. Then the grep filter applies a regular expression rule over the log field created by the tail plugin and only passes records with a field value starting with aa:

$ bin/fluent-bit -i tail -p 'path=lines.txt' -F grep -p 'regex=log aa' -m '*' -o stdout

Configuration file

fluent-bit.conf

[SERVICE]
    parsers_file /path/to/parsers.conf

[INPUT]
    name   tail
    path   lines.txt
    parser json

[FILTER]
    name   grep
    match  *
    regex  log aa

[OUTPUT]
    name   stdout
    match  *

fluent-bit.yaml

service:
    parsers_file: /path/to/parsers.conf
pipeline:
    inputs:
        - name: tail
          path: lines.txt
          parser: json
    filters:
        - name: grep
          match: '*'
          regex: log aa
    outputs:
        - name: stdout
          match: '*'

The filter lets you use multiple rules which are applied in order. You can have as many Regex and Exclude entries as required.

Nested fields example

To match or exclude records based on nested values, you can use Record Accessor format as the KEY name.

Consider the following record example:

{
    "log": "something",
    "kubernetes": {
        "pod_name": "myapp-0",
        "namespace_name": "default",
        "pod_id": "216cd7ae-1c7e-11e8-bb40-000c298df552",
        "labels": {
            "app": "myapp"
        },
        "host": "minikube",
        "container_name": "myapp",
        "docker_id": "370face382c7603fdd309d8c6aaaf434fd98b92421ce"
    }
}

For example, to exclude records that match the nested field kubernetes.labels.app, use the following rule:

fluent-bit.conf

[FILTER]
    Name    grep
    Match   *
    Exclude $kubernetes['labels']['app'] myapp

fluent-bit.yaml

    filters:
        - name: grep
          match: '*'
          exclude: $kubernetes['labels']['app'] myapp

Excluding records with missing or invalid fields

You might want to drop records that are missing certain keys.

One way to do this is to exclude with a regex that matches anything. A missing key fails this check.

The followinfg example checks for a specific valid value for the key:

fluent-bit.conf

# Use Grep to verify the contents of the iot_timestamp value.
# If the iot_timestamp key does not exist, this will fail
# and exclude the row.
[FILTER]
    Name                     grep
    Alias                    filter-iots-grep
    Match                    iots_thread.*
    Regex                    iot_timestamp ^\d{4}-\d{2}-\d{2}

fluent-bit.yaml

    filters:
        - name: grep
          alias: filter-iots-grep
          match: iots_thread.*
          regex: iot_timestamp ^\d{4}-\d{2}-\d{2}

The specified key iot_timestamp must match the expected expression. If it doesn't, or is missing or empty, then it will be excluded.

Multiple conditions

If you want to set multiple Regex or Exclude, use the Logical_Op property to use a logical conjuction or disjunction.

If Logical_Op is set, setting both Regex and Exclude results in an error.

fluent-bit.conf

[INPUT]
    Name dummy
    Dummy {"endpoint":"localhost", "value":"something"}
    Tag dummy

[FILTER]
    Name grep
    Match *
    Logical_Op or
    Regex value something
    Regex value error

[OUTPUT]
    Name stdout

fluent-bit.yaml

pipeline:
    inputs:
        - name: dummy
          dummy: '{"endpoint":"localhost", "value":"something"}'
          tag: dummy
    filters:
        - name: grep
          match: '*'
          logical_op: or
          regex:
            - value something
            - value error
    outputs:
        - name: stdout

The output looks similar to:

Fluent Bit v2.0.9
* Copyright (C) 2015-2022 The Fluent Bit Authors
* Fluent Bit is a CNCF sub-project under the umbrella of Fluentd
* https://fluentbit.io

[2023/01/22 09:46:49] [ info] [fluent bit] version=2.0.9, commit=16eae10786, pid=33268
[2023/01/22 09:46:49] [ info] [storage] ver=1.2.0, type=memory, sync=normal, checksum=off, max_chunks_up=128
[2023/01/22 09:46:49] [ info] [cmetrics] version=0.5.8
[2023/01/22 09:46:49] [ info] [ctraces ] version=0.2.7
[2023/01/22 09:46:49] [ info] [input:dummy:dummy.0] initializing
[2023/01/22 09:46:49] [ info] [input:dummy:dummy.0] storage_strategy='memory' (memory only)
[2023/01/22 09:46:49] [ info] [filter:grep:grep.0] OR mode
[2023/01/22 09:46:49] [ info] [sp] stream processor started
[2023/01/22 09:46:49] [ info] [output:stdout:stdout.0] worker #0 started
[0] dummy: [1674348410.558341857, {"endpoint"=>"localhost", "value"=>"something"}]
[0] dummy: [1674348411.546425499, {"endpoint"=>"localhost", "value"=>"something"}]