报错信息

Traceback (most recent call last):
    17: from /Users/john.lee/.rvm/gems/ruby-2.7.0-preview1/bin/ruby_executable_hooks:24:in `<main>'
    16: from /Users/john.lee/.rvm/gems/ruby-2.7.0-preview1/bin/ruby_executable_hooks:24:in `eval'
    15: from /Users/john.lee/.rvm/gems/ruby-2.7.0-preview1/bin/pod:25:in `<main>'
    14: from /Users/john.lee/.rvm/gems/ruby-2.7.0-preview1/bin/pod:25:in `load'
    13: from /Users/john.lee/.rvm/gems/ruby-2.7.0-preview1/gems/cocoapods-1.11.3/bin/pod:36:in `<top (required)>'
    12: from /Users/john.lee/.rvm/rubies/ruby-2.7.0-preview1/lib/ruby/site_ruby/2.7.0/rubygems/core_ext/kernel_require.rb:85:in `require'
    11: from /Users/john.lee/.rvm/rubies/ruby-2.7.0-preview1/lib/ruby/site_ruby/2.7.0/rubygems/core_ext/kernel_require.rb:85:in `require'
    10: from /Users/john.lee/.rvm/gems/ruby-2.7.0-preview1/gems/cocoapods-1.11.3/lib/cocoapods.rb:9:in `<top (required)>'
     9: from /Users/john.lee/.rvm/rubies/ruby-2.7.0-preview1/lib/ruby/site_ruby/2.7.0/rubygems/core_ext/kernel_require.rb:85:in `require'
     8: from /Users/john.lee/.rvm/rubies/ruby-2.7.0-preview1/lib/ruby/site_ruby/2.7.0/rubygems/core_ext/kernel_require.rb:85:in `require'
     7: from /Users/john.lee/.rvm/rubies/ruby-2.7.0-preview1/lib/ruby/gems/2.7.0/gems/activesupport-6.1.7/lib/active_support/core_ext/array/conversions.rb:3:in `<top (required)>'
     6: from /Users/john.lee/.rvm/rubies/ruby-2.7.0-preview1/lib/ruby/site_ruby/2.7.0/rubygems/core_ext/kernel_require.rb:85:in `require'
     5: from /Users/john.lee/.rvm/rubies/ruby-2.7.0-preview1/lib/ruby/site_ruby/2.7.0/rubygems/core_ext/kernel_require.rb:85:in `require'
     4: from /Users/john.lee/.rvm/rubies/ruby-2.7.0-preview1/lib/ruby/gems/2.7.0/gems/activesupport-6.1.7/lib/active_support/xml_mini.rb:11:in `<top (required)>'
     3: from /Users/john.lee/.rvm/rubies/ruby-2.7.0-preview1/lib/ruby/gems/2.7.0/gems/activesupport-6.1.7/lib/active_support/xml_mini.rb:17:in `<module:ActiveSupport>'
     2: from /Users/john.lee/.rvm/rubies/ruby-2.7.0-preview1/lib/ruby/gems/2.7.0/gems/activesupport-6.1.7/lib/active_support/xml_mini.rb:94:in `<module:XmlMini>'
     1: from /Users/john.lee/.rvm/rubies/ruby-2.7.0-preview1/lib/ruby/gems/2.7.0/gems/activesupport-6.1.7/lib/active_support/core_ext/module/delegation.rb:244:in `delegate'
/Users/john.lee/.rvm/rubies/ruby-2.7.0-preview1/lib/ruby/gems/2.7.0/gems/activesupport-6.1.7/lib/active_support/core_ext/module/delegation.rb:244:in `module_eval': /Users/john.lee/.rvm/rubies/ruby-2.7.0-preview1/lib/ruby/gems/2.7.0/gems/activesupport-6.1.7/lib/active_support/xml_mini.rb:94: syntax error, unexpected (..., expecting ')' (SyntaxError)
def parse(...);  _ = backend;  _.parse(......
          ^~~
/Users/john.lee/.rvm/rubies/ruby-2.7.0-preview1/lib/ruby/gems/2.7.0/gems/activesupport-6.1.7/lib/active_support/xml_mini.rb:94: syntax error, unexpected ')'
....);  _ = backend;  _.parse(...);rescue NoMethodError => e;  ...
...                          

问题原因：版本的问题，更换下版本。

我的解决步骤如下：

1.通过rvm list known查看下ruby的版本列表
2.再通过rvm use ruby-2.7.0 --default 设置某个为默认的版本
3.然后我执行pod,发现又报错了，报错如下：
Traceback (most recent call last):
    4: from /Users/john.lee/.rvm/rubies/ruby-2.7.0/bin/ruby_executable_hooks:22:in `<main>'
    3: from /Users/john.lee/.rvm/rubies/ruby-2.7.0/bin/ruby_executable_hooks:22:in `eval'
    2: from /usr/local/bin/pod:23:in `<main>'
    1: from /Users/john.lee/.rvm/rubies/ruby-2.7.0/lib/ruby/2.7.0/rubygems.rb:294:in `activate_bin_path'
/Users/john.lee/.rvm/rubies/ruby-2.7.0/lib/ruby/2.7.0/rubygems.rb:275:in `find_spec_for_exe': can't find gem cocoapods (>= 0.a) with executable pod (Gem::GemNotFoundException)

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提示为gem不能找到cocopods,不能执行
4. 执行gem source 查找当前源 我的是https://gems.ruby-china.com 没有问题，有多余的可以删掉
5.执行更新sudo gem update --system 
6. 安装cocopods sudo gem install -n /usr/local/bin cocoapods