Basicly the ruby in Raspberry Pi is using old version of Ruby.

So let's upgrade our Ruby to latest version.

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1. Check version of current use ruby
$ which ruby
/usr/bin/ruby

$ readlinl -f /usr/bin/ruby
/usr/bin/ruby2.1

$ dpkg -S /usr/bin/ruby2.1
ruby2.1: /usr/bin/ruby2.1

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2. Uninstall current use ruby
$ apt-get purge ruby2.1

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3. Install latest ruby using RVM
Get the key server.  (Can get from here: https://rvm.io/ )
$ gpg --keyserver hkp://keys.gnupg.net --recv-keys 409B6B1796C275462A1703113804BB82D39DC0E3 7D2BAF1CF37B13E2069D6956105BD0E739499BDB

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4. Download RVM

$ curl -sSL https://get.rvm.io | bash -s stable --ruby

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4. Show list version of ruby
$ rvm list known

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5. Install the lastest ruby version
$ rvm install 2.3.3

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6. After done install check the ruby version is use
$ ruby -v

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Done. You should have the latest version of ruby.

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