如果执行sudo gem install命令的时候提示权限问题

sudo gem install cocoapods
ERROR:  While executing gem ... (Errno::EPERM)
    Operation not permitted - /usr/bin/pod

解决方法是在.bash_profile中写入以下内容

export GEM_HOME=$HOME/.gem
export PATH=$GEM_HOME/bin:$PATH

然后执行source命令

source .bash_profile

如果之前安装了该gem，建议先卸载之前的gem，然后重新安装

sudo gem uninstall cocoapods
gem install cocoapods