Install plugin using gem. GemNotFound

[rschirin (Robert)]

Hi,
I'm using logstash 5.6.5 on Centos7 and I need to use elasticsearch filter so I'm trying to install this plugin.
If I try the command l

logstash-plugin install elasticsearch-filter

I receive the warning to check

gem install logstash-core -v 5.6.5

So, first of all, I installed Ruby with yum.
Unfortunately, when I try command

gem install logstash-core -v 5.6.5

I receive the message that logstash-core is available just for java platform.
What does it mean? What should I do? I didn't find anything in the official doc (how is it possible?)
Should I install jruby and not Ruby?

[rschirin (Robert)]

update: at the beginning, using ./logstash-plugin list command I was able to see the complete list of installed plugins.
after that I installed ruby/gem I'm facing another issue and list is not available:

Bundler::GemNotFound: Could not find gem 'logstash-filter-elasticsearch (>= 0) java' in any of the gem sources listed in your Gemfile or installed on this machine.
  verify_gemfile_dependencies_are_found! at /usr/share/logstash/vendor/bundle/jruby/1.9/gems/bundler-1.9.10/lib/bundler/resolver.rb:328
                                    each at org/jruby/RubyArray.java:1613
  verify_gemfile_dependencies_are_found! at /usr/share/logstash/vendor/bundle/jruby/1.9/gems/bundler-1.9.10/lib/bundler/resolver.rb:307
                                   start at /usr/share/logstash/vendor/bundle/jruby/1.9/gems/bundler-1.9.10/lib/bundler/resolver.rb:199
                                 resolve at /usr/share/logstash/vendor/bundle/jruby/1.9/gems/bundler-1.9.10/lib/bundler/resolver.rb:182
                                 resolve at /usr/share/logstash/vendor/bundle/jruby/1.9/gems/bundler-1.9.10/lib/bundler/definition.rb:192
                                   specs at /usr/share/logstash/vendor/bundle/jruby/1.9/gems/bundler-1.9.10/lib/bundler/definition.rb:132
                               specs_for at /usr/share/logstash/vendor/bundle/jruby/1.9/gems/bundler-1.9.10/lib/bundler/definition.rb:177
                         requested_specs at /usr/share/logstash/vendor/bundle/jruby/1.9/gems/bundler-1.9.10/lib/bundler/definition.rb:166
                         requested_specs at /usr/share/logstash/vendor/bundle/jruby/1.9/gems/bundler-1.9.10/lib/bundler/environment.rb:18
                                   setup at /usr/share/logstash/vendor/bundle/jruby/1.9/gems/bundler-1.9.10/lib/bundler/runtime.rb:13
                                   setup at /usr/share/logstash/vendor/bundle/jruby/1.9/gems/bundler-1.9.10/lib/bundler.rb:122
                                  setup! at /usr/share/logstash/lib/bootstrap/bundler.rb:67
                                 execute at /usr/share/logstash/lib/pluginmanager/list.rb:17
                                     run at /usr/share/logstash/vendor/bundle/jruby/1.9/gems/clamp-0.6.5/lib/clamp/command.rb:67
                                 execute at /usr/share/logstash/vendor/bundle/jruby/1.9/gems/clamp-0.6.5/lib/clamp/subcommand/execution.rb:11
                                     run at /usr/share/logstash/vendor/bundle/jruby/1.9/gems/clamp-0.6.5/lib/clamp/command.rb:67
                                     run at /usr/share/logstash/vendor/bundle/jruby/1.9/gems/clamp-0.6.5/lib/clamp/command.rb:132
                                  (root) at /usr/share/logstash/lib/pluginmanager/main.rb:48

can someone help me?