fluent/fluentd · error · Fluent::ConfigError

regexp#{i} does not contain 2 parameters

Error message

regexp#{i} does not contain 2 parameters

What it means

The grep filter's deprecated numbered parameters (regexp1..regexp20) take a value of the form 'key pattern' and are parsed with String#split(/ /, 2). If the value contains no space, the regexp capture is nil and configure raises Fluent::ConfigError because the directive does not carry both required parameters.

Source

Thrown at lib/fluent/plugin/filter_grep.rb:99

        desc "The field name to which the regular expression is applied."
        config_param :key, :string
        desc "The regular expression."
        config_param :pattern, :regexp
      end
    end

    def configure(conf)
      super

      regexp_and_conditions = {}
      regexp_or_conditions = {}
      exclude_and_conditions = {}
      exclude_or_conditions = {}

      (1..REGEXP_MAX_NUM).each do |i|
        next unless conf["regexp#{i}"]
        key, regexp = conf["regexp#{i}"].split(/ /, 2)
        raise Fluent::ConfigError, "regexp#{i} does not contain 2 parameters" unless regexp
        raise Fluent::ConfigError, "regexp#{i} contains a duplicated key, #{key}" if regexp_and_conditions[key]
        regexp_and_conditions[key] = Expression.new(record_accessor_create(key), Regexp.compile(regexp))
      end

      (1..REGEXP_MAX_NUM).each do |i|
        next unless conf["exclude#{i}"]
        key, exclude = conf["exclude#{i}"].split(/ /, 2)
        raise Fluent::ConfigError, "exclude#{i} does not contain 2 parameters" unless exclude
        raise Fluent::ConfigError, "exclude#{i} contains a duplicated key, #{key}" if exclude_or_conditions[key]
        exclude_or_conditions[key] = Expression.new(record_accessor_create(key), Regexp.compile(exclude))
      end

      if @regexps.size > 1
        log.info "Top level multiple <regexp> is interpreted as 'and' condition"
      end
      @regexps.each do |e|
        raise Fluent::ConfigError, "Duplicate key: #{e.key}" if regexp_and_conditions.key?(e.key)
        regexp_and_conditions[e.key] = Expression.new(record_accessor_create(e.key), e.pattern)

View on GitHub (pinned to dd45c6e18d)

Solutions

1. Supply both tokens: regexp1 message error
2. Better: migrate to the modern section syntax <regexp> key message pattern /error/
3. Run fluentd --dry-run to validate before deploy
4. If the pattern itself contains spaces, keep it on the same line after the key (split limit 2 keeps the rest intact)

Example fix

# before
<filter app.**>
  @type grep
  regexp1 message
</filter>

# after
<filter app.**>
  @type grep
  <regexp>
    key message
    pattern /error/
  </regexp>
</filter>

# Lint deprecated grep directives before deploy
(1..20).each do |i|
  %W[regexp#{i} exclude#{i}].each do |k|
    next unless (v = conf[k])
    abort "#{k} must be '<key> <pattern>': got '#{v}'" unless v.include?(' ')
  end
end

# or simply:
system('fluentd --dry-run -c /etc/fluent/fluent.conf') or abort 'config invalid'

begin
  Fluent::Plugin::GrepFilter.new.configure(conf)
rescue Fluent::ConfigError => e
  abort "grep filter config rejected: #{e.message}" # message includes the regexpN index
end

When it happens

Trigger: A config line like regexp1 message (field name only, no pattern) or regexp1 "message" where quoting removed the intended space; any regexpN value that splits into fewer than 2 tokens. Note regexpN itself is deprecated in favor of <regexp> sections.

Common situations: Migrating old v0.12 grep configs where a pattern was accidentally dropped; YAML/erb templating that renders an empty pattern variable; quoting mistakes where the pattern is in a separate quoted string that gets lost.

Understand the failure class

Background: Config validation failed: what "invalid value for {key}" and settings-rejection errors mean across 19 open-source libraries — this error's family across 19 libraries.

Related errors

• exclude#{i} does not contain 2 parameters
• regexp#{i} contains a duplicated key, #{key}
• exclude#{i} contains a duplicated key, #{key}
• Duplicate key: #{e.key}
• Do not specify both <regexp> and <exclude> in <and>

AI-assisted analysis of fluent/fluentd@dd45c6e18d (2026-08-21). Data as JSON: /api/errors/375e4b65d8c78e3b. Report an issue: GitHub.