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Regular Expression

The Regex parser lets you define a custom Ruby regular expression that uses a named capture feature to define which content belongs to which key name.

Use Tail Multiline when you need to support regexes across multiple lines from a tail. The Tail input plugin treats each line as a separate entity.

{% hint style="warning" %} Security Warning: Onigmo is a backtracking regex engine. When using expensive regex patterns Onigmo can take a long time to perform pattern matching. Read "ReDoS" on OWASP for additional information. {% end hint %}

Setting the format to regex requires a regex configuration key.

Configuration Parameters

The regex parser supports the following configuration parameters:

Key Description Default Value
Skip_Empty_Values If enabled, the parser ignores empty value of the record. True

Fluent Bit uses the Onigmo regular expression library on Ruby mode.

You can use only alphanumeric characters and underscore in group names. For example, a group name like (?<user-name>.*) causes an error due to the invalid dash (-) character. Use the Rubular web editor to test your expressions.

The following parser configuration example provides rules that can be applied to an Apache HTTP Server log entry:

[PARSER]
    Name   apache
    Format regex
    Regex  ^(?<host>[^ ]*) [^ ]* (?<user>[^ ]*) \[(?<time>[^\]]*)\] "(?<method>\S+)(?: +(?<path>[^\"]*?)(?: +\S*)?)?" (?<code>[^ ]*) (?<size>[^ ]*)(?: "(?<referer>[^\"]*)" "(?<agent>[^\"]*)")?$
    Time_Key time
    Time_Format %d/%b/%Y:%H:%M:%S %z
    Types code:integer size:integer

As an example, review the following Apache HTTP Server log entry:

192.168.2.20 - - [29/Jul/2015:10:27:10 -0300] "GET /cgi-bin/try/ HTTP/1.0" 200 3395

This log entry doesn't provide a defined structure for Fluent Bit. Enabling the proper parser can help to make a structured representation of the entry:

[1154104030, {"host"=>"192.168.2.20",
              "user"=>"-",
              "method"=>"GET",
              "path"=>"/cgi-bin/try/",
              "code"=>"200",
              "size"=>"3395",
              "referer"=>"",
              "agent"=>""
              }
]