1. brewアップデート

brew update
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First, rewinding head to replay your work on top of it...
Fast-forwarded master to e126ec926b38ccfcc7c46d3ba32b85afd1ba63d2.
Current branch master is up to date.
Updated Homebrew from f47755f3 to e126ec92.
〜
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==> Deleted Formulae
aimage	    cmucl	darner	    jscoverage	lmutil	    mlxcc	nlopt
brainfuck   comparepdf	flex_sdk    jsl		metasploit  mt-daapd	pngrewrite

2. ruby-buildアップグレード

brew upgrade ruby-build
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==> Upgrading 1 outdated package, with result:
ruby-build 20131225.1
==> Upgrading ruby-build
==> Downloading https://github.com/sstephenson/ruby-build/archive/v20131225.1.tar.gz
######################################################################## 100.0%
==> ./install.sh
?  /usr/local/Cellar/ruby-build/20131225.1: 102 files, 448K, built in 2 seconds
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4. インストール可能リスト表示確認

rbenv install -l | grep 2.1.0
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  2.1.0
  2.1.0-dev
  2.1.0-preview1
  2.1.0-preview2
  2.1.0-rc1
  rbx-2.1.0
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5. Rubyインストール

RUBY_CONFIGURE_OPTS="--with-readline-dir=$(brew --prefix readline) --with-openssl-dir=$(brew --prefix openssl)" rbenv install 2.1.0

6. デフォルト使用設定

rbenv global 2.1.0
ruby -v
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ruby 2.1.0p0 (2013-12-25 revision 44422) [x86_64-darwin12.0]
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7. バージョン確認

rbenv version
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2.1.0 (set by /Users/shu/.rbenv/version)
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8. インストールしたRubyやGemのパスを通す

rbenv rehash