Cocoapods 安装指定版本

$ sudo gem install cocoapods --version 1.0.0

ERROR: While executing gem ... (Errno::EPERM)
Operation not permitted - /usr/bin/xcodeproj
权限报错
sudo gem install -n /usr/local/bin cocoapods --version 1.2.0

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问题1
xx$ gem install cocoapods -n /usr/local/bin
ERROR: While executing gem ... (Gem::UnsatisfiableDependencyError)
Unable to resolve dependency: 'cocoapods (= 1.5.0)' requires 'cocoapods-core (= 1.5.0)'

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可能是gem太旧，执行sudo gem update --system
再执行gem install cocoapods -n /usr/local/bin
就没有问题了