error1.
系统：10.13.6
命令：sudo gem install cocoapods
ERROR: While executing gem ... (Gem::FilePermissionError) You don't have write permissions for the /usr/bin directory.
执行此命令即可
sudo gem install cocoapods -n /usr/local/bin
error2.
系统：10.14.6
命令：sudo gem install cocoapods
$ sudo gem install cocoapods
Building native extensions. This could take a while...
ERROR: Error installing sass:
ERROR: Failed to build gem native extension.
current directory: /Library/Ruby/Gems/2.3.0/gems/ffi-1.11.1/ext/ffi_c
/System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/bin/ruby -I /Library/Ruby/Site/2.3.0 -r ./siteconf20191022-2775-1q9uxye.rb extconf.rb
mkmf.rb can't find header files for ruby at /System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/include/ruby.h
extconf failed, exit code 1
Gem files will remain installed in /Library/Ruby/Gems/2.3.0/gems/ffi-1.11.1 for inspection.
Results logged to /Library/Ruby/Gems/2.3.0/extensions/universal-darwin-18/2.3.0/ffi-1.11.1/gem_make.out
解决办法：执行下面命令按提示执行
open /Library/Developer/CommandLineTools/Packages/macOS_SDK_headers_for_macOS_10.14.pkg
error3.
[!] CDN: trunk Repo update failed - 24 error(s):
解决办法：Podfile文件中添加下面代码
source 'https://github.com/CocoaPods/Specs.git'
如果pod search有些库不正常，可以执行：
pod repo remove trunk
