升级10.13以后Pod命令失效，解决办法如下：

终端执行下列命令

1.brew link --overwrite cocoapods

尝试 Pod 命令是否已经恢复 ,若报错继续执行

2.brew install ruby

3.brew reinstall cocoapods

4.brew link --overwrite cocoapods

尝试 Pod 命令是否已经恢复

二、弄完之后如果报错

/usr/local/bin/pod: /usr/local/Cellar/cocoapods/1.5.3/libexec/bin/pod: /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/bin/ruby: bad interpreter: No such file or directory
/usr/local/bin/pod: line 2: /usr/local/Cellar/cocoapods/1.5.3/libexec/bin/pod: Undefined error: 0

可以参考下面两个文章,我也对两篇文章有需要的地方做了总结，所以也可以继续看我的文章第三步骤
文章一/
文章二/WainYan

三、更新gem

1.查看gem版本号

gem -v

2.查看ruby源。

gem sources -l

3.替换ruby源(如果是https://gems.ruby-china.com, 则跳过3、4步)

gem sources --remove  https://gems.ruby-china.org
gem sources --add  https://gems.ruby-china.com

注意是https://gems.ruby-china.com 不是https://gems.ruby-china.org.

4.确保ruby源是https://gems.ruby-china.com

gem sources -l

5.更新gem版本

gem update --system
如果错误：
>ERROR:  While executing gem ... (Gem::FilePermissionError)
    You don't have write permissions for the /Library/Ruby/Gems/2.3.0 directory.

使用：sudo gem update --system

6.打印gem版本号是否成功

gem -v

如果更新完报错如下：那么就要像我一样参考这篇“时苒君”的文章了，总结为一句话，看步骤四

mayonggang@bogon digital_city_IAP % pod update --no-repo-update --verbose
Traceback (most recent call last):
    5: from /usr/local/bin/pod:23:in `<main>'
    4: from /usr/local/bin/pod:23:in `load'
    3: from /Library/Ruby/Gems/2.6.0/gems/cocoapods-1.7.5/bin/pod:55:in `<top (required)>'
    2: from /Library/Ruby/Gems/2.6.0/gems/cocoapods-1.7.5/lib/cocoapods/command.rb:49:in `run'
    1: from /Library/Ruby/Gems/2.6.0/gems/cocoapods-1.7.5/lib/cocoapods/command.rb:130:in `verify_minimum_git_version!'
/Library/Ruby/Gems/2.6.0/gems/cocoapods-1.7.5/lib/cocoapods/command.rb:118:in `git_version': Failed to extract git version from `git --version` ("xcrun: error: invalid active developer path (/Library/Developer/CommandLineTools), missing xcrun at: /Library/Developer/CommandLineTools/usr/bin/xcrun\n") (RuntimeError)

下图：