fluent/fluentd · error · Fluent::ConfigError

invalid match - regex

Error message

invalid match - regex

What it means

In <match PATTERN>, a pattern starting with '/' switches GlobMatchPattern into regex mode, where the value must also end with '/' so the content between the slashes becomes an anchored regex (\A...\Z wrapped). A leading '/' without a trailing '/' raises this ConfigError at config setup. This rule exists because tags may contain regex metacharacters, so globs and regexes are disambiguated by the slash delimiters.

Source

Thrown at lib/fluent/match.rb:41

        GlobMatchPattern.new(str)
      end
    end
  end

  class AllMatchPattern < MatchPattern
    def match(str)
      true
    end
  end

  class GlobMatchPattern < MatchPattern
    def initialize(pat)
      if pat.start_with?('/')
        if pat.end_with?('/')
          @regex = Regexp.new("\\A"+pat[1..-2]+"\\Z")
          return
        else
          raise Fluent::ConfigError,  "invalid match - regex"
        end
      end

      stack = []
      regex = ['']
      escape = false
      dot = false

      i = 0
      while i < pat.length
        c = pat[i,1]

        if escape
          regex.last << Regexp.escape(c)
          escape = false
          i += 1
          next

View on GitHub (pinned to dd45c6e18d)

Solutions

1. Close the delimited regex: <match /app\.log/>
2. If glob semantics are wanted and the tag does not start with '/', use a plain glob like app.*
3. For tags that genuinely start with '/', match them with an explicit regex: <match /\/var\/log\/.*/>
4. Remember the regex is fully anchored; write ^/$ anchors are unnecessary

Example fix

# before
<match /app.log>
  @type stdout
</match>

# after
<match /app\.log/>
  @type stdout
</match>

pat = '/app\.log/'
raise ArgumentError, 'regex match pattern must end with /' if pat.start_with?('/') && !pat.end_with?('/')
# also accepts /pat/i, /pat/m
Regexp.new('\\A' + pat[1..-2].gsub(/([im])\z/, '') + '\\Z') rescue raise ArgumentError, 'bad match regex'

When it happens

Trigger: <match /app.log> (forgot the closing slash); <match /var/log/*> intending a glob for slash-prefixed syslog-style tags; a regex copied from Ruby source (where no delimiters are used) into <match> without wrapping slashes.

Common situations: Writing regex tag matches by hand; tags that begin with '/' (syslog, some container log drivers) colliding with delimiter syntax; mixing up glob '*' semantics (matches dots too, unlike shell globs) and switching to regex mid-edit.

Related errors

• Missing <match> sections in <label #{@context}> section
• Unknown #{@kind} plugin '#{type}'. Run 'gem search -rd fluen
• Missing '@type' parameter on <#{e.name}> directive
• 'format' parameter is required
• both of utc and localtime are specified, use only one of the

AI-assisted analysis of fluent/fluentd@dd45c6e18d (2026-08-21). Data as JSON: /api/errors/998288517b908ecc. Report an issue: GitHub.