Error while connecting Logstash and Elasticsearch - elasticsearch

Question

I am very very new to ELK, I installed ELK version 5.6.12 on CentOS sever. Elasticsearch and Kibana works fine. But I cannot connect Logstash to Elastic search.
I have set environment variable as
export JAVA_HOME=/usr/local/jdk1.8.0_131
export PATH=/usr/local/jdk1.8.0_131/bin:$PATH
I run simple test :
bin/logstash -e 'input { stdin { } } output { elasticsearch { host => localhost:9200 protocol => "http" port => "9200" } }'
I get error :
WARNING: Could not find logstash.yml which is typically located in
$LS_HOME/config or /etc/logstash. You can specify the path using --
path.settings. Continuing using the defaults
Could not find log4j2 configuration at path
/etc/logstash/logstash.yml/log4j2.properties. Using default config which
logs errors to the console
Simple "slash" mentioned in official documentation of Logstash works like following :
$bin/logstash -e 'input { stdin { } } output { stdout {} }'
Hello
WARNING: Could not find logstash.yml which is typically located in
$LS_HOME/config or /etc/logstash. You can specify the path using --
path.settings. Continuing using the defaults Could not find log4j2
configuration at path /usr/share/logstash/config/log4j2.properties.
Using default config which logs errors to the console
The stdin plugin is now waiting for input: {
"#version" => "1",
"host" => "localhost",
"#timestamp" => 2018-11-01T04:44:58.648Z,
"message" => "Hello" }
What could be the problem?