1.先安装新版Xcode
2.配置rvm ($为终端自带，不用copy)
rvm是一个便捷的多版本 ruby 环境的管理和切换工具
在终端控制台命令：
$ curl -sSLhttps://get.rvm.io| bash -s stable之后按回车键
3.安装 ruby
列出 ruby 可安装的版本信息 (这里安装的是 2.4.4 的)
$ rvm list known
结果为：
# MRI Rubies
[ruby-]1.8.6[-p420]
[ruby-]1.8.7[-head]# security released on head
[ruby-]1.9.1[-p431]
[ruby-]1.9.2[-p330]
[ruby-]1.9.3[-p551]
[ruby-]2.0.0[-p648]
[ruby-]2.1[.10]
[ruby-]2.2[.10]
[ruby-]2.3[.7]
[ruby-]2.4[.4]
[ruby-]2.5[.1]
[ruby-]2.6[.0-preview2]
ruby-head
安装一个ruby版本
$ rvm install 2.4.4 (也可尝试安装2.6.0 我没有尝试)
如果想设置为默认版本，可以用这条命令来完成
$ rvm use 2.4.4 --default
如果出现以下结果，则没有安装homebrew
No binary rubies available for: osx/10.13/x86_64/ruby-2.4.4.
Continuing with compilation. Please read 'rvm help mount' to get more information on binary rubies.
Checking requirements for osx.
About to install Homebrew,press `Enter` for default installation in `/usr/local`,
type new path if you wish custom Homebrew installation(the path needs to be writable for user)
: /usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"
mkdir: /usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)": Operation not permitted
Requirements installation failed with status: 1.
安装Homebrew，通过命令行即可，打开终端输入
/usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"
出现下面内容即OK
==>Migrating /Library/Caches/Homebrew to /Users/tiantian/Library/Caches/Homebrew...
==>Deleting /Library/Caches/Homebrew...
Already up-to-date.
==> Installation successful!
安装homebrew后，再次执行 $ rvm install 2.4.0
直到出现
ruby-2.4.4 - #adjusting #shebangs for(gem irb erb ri rdoc testrb rake).
Install of ruby-2.4.4 - #complete
安装ruby成功
4. 最后就是最重要的安装cocoapods了
$ sudo gem install cocoapods
Done installing documentation for nanaimo,colored2,claide,CFPropertyList,xcodeproj,ruby-macho,nap,molinillo,gh_inspector,fourflusher,escape,cocoapods-try,netrc,cocoapods-trunk,cocoapods-stats,cocoapods-search,cocoapods-plugins,cocoapods-downloader,cocoapods-deintegrate,fuzzy_match,thread_safe,tzinfo,i18n,activesupport,cocoapods-core,cocoapods after 19 seconds
意味你安装成功了！！！
