diff --git a/lib/fluent/command/ctl.rb b/lib/fluent/command/ctl.rb
index e4d9130187..f908d40f05 100644
--- a/lib/fluent/command/ctl.rb
+++ b/lib/fluent/command/ctl.rb
@@ -92,7 +92,7 @@ def usage(msg = nil)
 
     def call
       if Fluent.windows?
-        if @pid_or_svcname =~ /^[0-9]+$/
+        if /^[0-9]+$/.match?(@pid_or_svcname)
           # Use as PID
           return call_windows_event(@command, "fluentd_#{@pid_or_svcname}")
         end
@@ -172,7 +172,7 @@ def parse_options!
         usage("PID or SVCNAME isn't specified!") if @pid_or_svcname.nil? || @pid_or_svcname.empty?
       else
         usage("PID isn't specified!") if @pid_or_svcname.nil? || @pid_or_svcname.empty?
-        usage("Invalid PID: #{pid}") unless @pid_or_svcname =~ /^[0-9]+$/
+        usage("Invalid PID: #{pid}") unless /^[0-9]+$/.match?(@pid_or_svcname)
       end
     end
   end
diff --git a/lib/fluent/command/plugin_config_formatter.rb b/lib/fluent/command/plugin_config_formatter.rb
index aa61c5711d..00d660da0b 100644
--- a/lib/fluent/command/plugin_config_formatter.rb
+++ b/lib/fluent/command/plugin_config_formatter.rb
@@ -61,7 +61,7 @@ def call
     @plugin.class.ancestors.reverse_each do |plugin_class|
       next unless plugin_class.respond_to?(:dump_config_definition)
       unless @verbose
-        next if plugin_class.name =~ /::PluginHelper::/
+        next if /::PluginHelper::/.match?(plugin_class.name)
       end
       dumped_config_definition = plugin_class.dump_config_definition
       dumped_config[plugin_class.name] = dumped_config_definition unless dumped_config_definition.empty?
diff --git a/lib/fluent/config/dsl.rb b/lib/fluent/config/dsl.rb
index fc4b158ce7..f23a2688ed 100644
--- a/lib/fluent/config/dsl.rb
+++ b/lib/fluent/config/dsl.rb
@@ -110,7 +110,7 @@ def method_missing(name, *args, &block)
 
         def include(*args)
           ::Kernel.raise ::ArgumentError, "#{name} block requires arguments for include path" if args.nil? || args.size != 1
-          if args.first =~ /\.rb$/
+          if /\.rb$/.match?(args.first)
             path = File.expand_path(args.first)
             data = File.read(path)
             self.instance_eval(data, path)
diff --git a/lib/fluent/config/v1_parser.rb b/lib/fluent/config/v1_parser.rb
index 7f36b44e43..7432e6c924 100644
--- a/lib/fluent/config/v1_parser.rb
+++ b/lib/fluent/config/v1_parser.rb
@@ -150,8 +150,8 @@ def parse_include(attrs, elems)
       def eval_include(attrs, elems, uri)
         # replace space(s)(' ') with '+' to prevent invalid uri due to space(s).
         # See: https://github.com/fluent/fluentd/pull/2780#issuecomment-576081212
-        u = URI.parse(uri.gsub(/ /, '+'))
-        if u.scheme == 'file' || (!u.scheme.nil? && u.scheme.length == 1) || u.path == uri.gsub(/ /, '+') # file path
+        u = URI.parse(uri.tr(' ', '+'))
+        if u.scheme == 'file' || (!u.scheme.nil? && u.scheme.length == 1) || u.path == uri.tr(' ', '+') # file path
           # When the Windows absolute path then u.scheme.length == 1
           # e.g. C:
           path = URI.decode_www_form_component(u.path)
diff --git a/lib/fluent/counter/server.rb b/lib/fluent/counter/server.rb
index c35d3073d2..359c6a0df2 100644
--- a/lib/fluent/counter/server.rb
+++ b/lib/fluent/counter/server.rb
@@ -27,7 +27,7 @@ class Server
       DEFAULT_PORT = 24321
 
       def initialize(name, opt = {})
-        raise 'Counter server name is invalid' unless Validator::VALID_NAME =~ name
+        raise 'Counter server name is invalid' unless Validator::VALID_NAME.match?(name)
         @name = name
         @opt = opt
         @addr = @opt[:addr] || DEFAULT_ADDR
diff --git a/lib/fluent/counter/validator.rb b/lib/fluent/counter/validator.rb
index 94ab6d2465..7e8fca91b8 100644
--- a/lib/fluent/counter/validator.rb
+++ b/lib/fluent/counter/validator.rb
@@ -82,7 +82,7 @@ def validate_key!(name)
           raise Fluent::Counter::InvalidParams.new('The type of `key` should be String')
         end
 
-        unless VALID_NAME =~ name
+        unless VALID_NAME.match?(name)
           raise Fluent::Counter::InvalidParams.new('`key` is the invalid format')
         end
       end
@@ -92,7 +92,7 @@ def validate_scope!(name)
           raise Fluent::Counter::InvalidParams.new('The type of `scope` should be String')
         end
 
-        unless VALID_SCOPE_NAME =~ name
+        unless VALID_SCOPE_NAME.match?(name)
           raise Fluent::Counter::InvalidParams.new('`scope` is the invalid format')
         end
       end
@@ -109,7 +109,7 @@ def validate_name!(hash)
           raise Fluent::Counter::InvalidParams.new('The type of `name` should be String')
         end
 
-        unless VALID_NAME =~ name
+        unless VALID_NAME.match?(name)
           raise Fluent::Counter::InvalidParams.new("`name` is the invalid format")
         end
       end
diff --git a/lib/fluent/engine.rb b/lib/fluent/engine.rb
index c4202c41d8..afac3167ca 100644
--- a/lib/fluent/engine.rb
+++ b/lib/fluent/engine.rb
@@ -68,7 +68,7 @@ def log
     end
 
     def parse_config(io, fname, basepath = Dir.pwd, v1_config = false)
-      if fname =~ /\.rb$/
+      if /\.rb$/.match?(fname)
         require 'fluent/config/dsl'
         Config::DSL::Parser.parse(io, File.join(basepath, fname))
       else
diff --git a/lib/fluent/match.rb b/lib/fluent/match.rb
index 17122e07ef..7b6c076adc 100644
--- a/lib/fluent/match.rb
+++ b/lib/fluent/match.rb
@@ -115,7 +115,7 @@ def initialize(pat)
           stack.last << regex.pop
           regex.push ''
 
-        elsif c =~ /[a-zA-Z0-9_]/
+        elsif /[a-zA-Z0-9_]/.match?(c)
           regex.last << c
 
         else
diff --git a/lib/fluent/plugin/base.rb b/lib/fluent/plugin/base.rb
index b0cee6ca03..eb20612a61 100644
--- a/lib/fluent/plugin/base.rb
+++ b/lib/fluent/plugin/base.rb
@@ -190,7 +190,7 @@ def called_in_test?
           # Thread::Backtrace::Location#path returns base filename or absolute path.
           # #absolute_path returns absolute_path always.
           # https://bugs.ruby-lang.org/issues/12159
-          if location.absolute_path =~ /\/test_[^\/]+\.rb$/ # location.path =~ /test_.+\.rb$/
+          if /\/test_[^\/]+\.rb$/.match?(location.absolute_path) # location.path =~ /test_.+\.rb$/
             return true
           end
         end
diff --git a/lib/fluent/plugin/filter_record_transformer.rb b/lib/fluent/plugin/filter_record_transformer.rb
index 02ba686a39..83af76ff6d 100644
--- a/lib/fluent/plugin/filter_record_transformer.rb
+++ b/lib/fluent/plugin/filter_record_transformer.rb
@@ -316,7 +316,7 @@ def expand(__str_to_eval__, tag, time, record, tag_parts, tag_prefix, tag_suffix
         end
 
         (Object.instance_methods).each do |m|
-          undef_method m unless m.to_s =~ /^__|respond_to_missing\?|object_id|public_methods|instance_eval|method_missing|define_singleton_method|respond_to\?|new_ostruct_member|^class$/
+          undef_method m unless /^__|respond_to_missing\?|object_id|public_methods|instance_eval|method_missing|define_singleton_method|respond_to\?|new_ostruct_member|^class$/.match?(m.to_s)
         end
       end
     end
diff --git a/lib/fluent/plugin/in_http.rb b/lib/fluent/plugin/in_http.rb
index 98961cf9e1..e738f2db69 100644
--- a/lib/fluent/plugin/in_http.rb
+++ b/lib/fluent/plugin/in_http.rb
@@ -428,7 +428,7 @@ def on_headers_complete(headers)
         @content_type = ""
         @content_encoding = ""
         headers.each_pair {|k,v|
-          @env["HTTP_#{k.gsub('-','_').upcase}"] = v
+          @env["HTTP_#{k.tr('-','_').upcase}"] = v
           case k
           when /\AExpect\z/i
             expect = v
@@ -439,9 +439,9 @@ def on_headers_complete(headers)
           when /\AContent-Encoding\Z/i
             @content_encoding = v
           when /\AConnection\Z/i
-            if v =~ /close/i
+            if /close/i.match?(v)
               @keep_alive = false
-            elsif v =~ /Keep-alive/i
+            elsif /Keep-alive/i.match?(v)
               @keep_alive = true
             end
           when /\AOrigin\Z/i
@@ -566,16 +566,16 @@ def on_message_complete
 
         if @format_name != 'default'
           params[EVENT_RECORD_PARAMETER] = @body
-        elsif @content_type =~ /^application\/x-www-form-urlencoded/
+        elsif /^application\/x-www-form-urlencoded/.match?(@content_type)
           params.update WEBrick::HTTPUtils.parse_query(@body)
         elsif @content_type =~ /^multipart\/form-data; boundary=(.+)/
           boundary = WEBrick::HTTPUtils.dequote($1)
           params.update WEBrick::HTTPUtils.parse_form_data(@body, boundary)
-        elsif @content_type =~ /^application\/json/
+        elsif /^application\/json/.match?(@content_type)
           params['json'] = @body
-        elsif @content_type =~ /^application\/msgpack/
+        elsif /^application\/msgpack/.match?(@content_type)
           params['msgpack'] = @body
-        elsif @content_type =~ /^application\/x-ndjson/
+        elsif /^application\/x-ndjson/.match?(@content_type)
           params['ndjson'] = @body
         end
         path_info = uri.path
@@ -585,7 +585,7 @@ def on_message_complete
           query_params = WEBrick::HTTPUtils.parse_query(uri.query)
 
           query_params.each_pair {|k,v|
-            params["QUERY_#{k.gsub('-','_').upcase}"] = v
+            params["QUERY_#{k.tr('-','_').upcase}"] = v
           }
         end
 
diff --git a/lib/fluent/plugin/in_tail.rb b/lib/fluent/plugin/in_tail.rb
index ef8246f7e8..88556ca6ab 100644
--- a/lib/fluent/plugin/in_tail.rb
+++ b/lib/fluent/plugin/in_tail.rb
@@ -781,7 +781,7 @@ def initialize(target_info, pe, log, read_from_head, follow_inodes, update_watch
       attr_accessor :group_watcher
 
       def tag
-        @parsed_tag ||= @path.tr('/', '.').gsub(/\.+/, '.').gsub(/^\./, '')
+        @parsed_tag ||= @path.tr('/', '.').squeeze('.').gsub(/^\./, '')
       end
 
       def register_watcher(watcher)
diff --git a/lib/fluent/plugin/out_exec_filter.rb b/lib/fluent/plugin/out_exec_filter.rb
index e5981d1eec..3428876dd0 100644
--- a/lib/fluent/plugin/out_exec_filter.rb
+++ b/lib/fluent/plugin/out_exec_filter.rb
@@ -163,7 +163,7 @@ def configure(conf)
                     0
                   elsif (@child_respawn == 'inf') || (@child_respawn == '-1')
                     -1
-                  elsif @child_respawn =~ /^\d+$/
+                  elsif /^\d+$/.match?(@child_respawn)
                     @child_respawn.to_i
                   else
                     raise ConfigError, "child_respawn option argument invalid: none(or 0), inf(or -1) or positive number"
diff --git a/lib/fluent/plugin/output.rb b/lib/fluent/plugin/output.rb
index 7b8a8ef997..0aed67db95 100644
--- a/lib/fluent/plugin/output.rb
+++ b/lib/fluent/plugin/output.rb
@@ -824,7 +824,7 @@ def extract_placeholders(str, chunk)
             if str.include?('${tag}')
               rvalue = rvalue.gsub('${tag}', metadata.tag)
             end
-            if str =~ CHUNK_TAG_PLACEHOLDER_PATTERN
+            if CHUNK_TAG_PLACEHOLDER_PATTERN.match?(str)
               hash = {}
               tag_parts = metadata.tag.split('.')
               tag_parts.each_with_index do |part, i|
diff --git a/lib/fluent/plugin/parser_json.rb b/lib/fluent/plugin/parser_json.rb
index 840f6a963c..829aa4b72a 100644
--- a/lib/fluent/plugin/parser_json.rb
+++ b/lib/fluent/plugin/parser_json.rb
@@ -60,7 +60,7 @@ def configure_json_parser(name)
       rescue LoadError => ex
         name = :yajl
         if log
-          if /\boj\z/ =~ ex.message
+          if /\boj\z/.match?(ex.message)
             log.info "Oj is not installed, and failing back to Yajl for json parser"
           else
             log.warn ex.message
diff --git a/lib/fluent/plugin_helper/record_accessor.rb b/lib/fluent/plugin_helper/record_accessor.rb
index 6c1210330b..9a37a60ff4 100644
--- a/lib/fluent/plugin_helper/record_accessor.rb
+++ b/lib/fluent/plugin_helper/record_accessor.rb
@@ -119,7 +119,7 @@ def self.parse_dot_notation(param)
         def self.validate_dot_keys(keys)
           keys.each { |key|
             next unless key.is_a?(String)
-            if /\s+/.match(key)
+            if /\s+/.match?(key)
               raise Fluent::ConfigError, "whitespace character is not allowed in dot notation. Use bracket notation: #{key}"
             end
           }
diff --git a/lib/fluent/plugin_id.rb b/lib/fluent/plugin_id.rb
index 87b1bc7ff1..af9b6019d3 100644
--- a/lib/fluent/plugin_id.rb
+++ b/lib/fluent/plugin_id.rb
@@ -49,7 +49,7 @@ def plugin_id_for_test?
         # Thread::Backtrace::Location#path returns base filename or absolute path.
         # #absolute_path returns absolute_path always.
         # https://bugs.ruby-lang.org/issues/12159
-        if location.absolute_path =~ /\/test_[^\/]+\.rb$/ # location.path =~ /test_.+\.rb$/
+        if /\/test_[^\/]+\.rb$/.match?(location.absolute_path) # location.path =~ /test_.+\.rb$/
           return true
         end
       end
diff --git a/test/plugin/test_base.rb b/test/plugin/test_base.rb
index 479ecc49f6..e6062a163b 100644
--- a/test/plugin/test_base.rb
+++ b/test/plugin/test_base.rb
@@ -108,7 +108,7 @@ class FluentPluginBaseTest::DummyPlugin2 < Fluent::Plugin::TestBase
     @p.extend m
     assert_equal [], logger.logs
 
-    ret = @p.string_safe_encoding("abc\xff.\x01f"){|s| s.split(/\./) }
+    ret = @p.string_safe_encoding("abc\xff.\x01f"){|s| s.split(".") }
     assert_equal ['abc?', "\u0001f"], ret
     assert_equal 1, logger.logs.size
     assert{ logger.logs.first.include?("invalid byte sequence is replaced in ") }
diff --git a/test/plugin_helper/test_server.rb b/test/plugin_helper/test_server.rb
index cb44b8363d..347938eca3 100644
--- a/test/plugin_helper/test_server.rb
+++ b/test/plugin_helper/test_server.rb
@@ -1329,7 +1329,7 @@ def assert_certificate(cert, expected_extensions)
           # OpenSSL 1.1.1: "TLSv1.2"
           if tls_version == "TLSv1/SSLv3" || tls_version == "TLSv1.2"
             matched = true
-            unless cipher_name.match(/#{conf.ciphers}/)
+            unless cipher_name.match?(/#{conf.ciphers}/)
               matched = false
               break
             end