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:
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:
[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 *
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:
# 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}
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.
[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
pipeline:inputs: - name:dummydummy:'{"endpoint":"localhost", "value":"something"}'tag:dummyfilters: - name:grepmatch:'*'logical_op:orregex: - value something - value erroroutputs: - 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"}]