cd /opt/logstash
env GEM_HOME=vendor/bundle/jruby/1.9 GEM_PATH="" java -jar vendor/jar/jruby-complete-1.7.11.jar -S gem install gemname

如果要安装本地宝石文件，请将文件路径放在GEM_PATH中。

If you're installing a local gem file, put the path to the file in GEM_PATH.