错误信息：
RuntimeError - [Xcodeproj] Unknown object version.
/Users/huangjing/.rvm/gems/ruby-2.0.0-p643@global/gems/xcodeproj-1.4.2/lib/xcodeproj/project.rb:217:in `initialize_from_file'
/Users/huangjing/.rvm/gems/ruby-2.0.0-p643@global/gems/xcodeproj-1.4.2/lib/xcodeproj/project.rb:102:in `open'
/Users/huangjing/.rvm/gems/ruby-2.0.0-p643@global/gems/cocoapods-1.1.1/lib/cocoapods/installer/analyzer.rb:855:in `block (2 levels) in inspect_targets_to_integrate'
/Users/huangjing/.rvm/gems/ruby-2.0.0-p643@global/gems/cocoapods-1.1.1/lib/cocoapods/installer/analyzer.rb:854:in `each'
/Users/huangjing/.rvm/gems/ruby-2.0.0-p643@global/gems/cocoapods-1.1.1/lib/cocoapods/installer/analyzer.rb:854:in `block in inspect_targets_to_integrate'
/Users/huangjing/.rvm/gems/ruby-2.0.0-p643@global/gems/cocoapods-1.1.1/lib/cocoapods/user_interface.rb:64:in `section'
/Users/huangjing/.rvm/gems/ruby-2.0.0-p643@global/gems/cocoapods-1.1.1/lib/cocoapods/installer/analyzer.rb:849:in `inspect_targets_to_integrate'
/Users/huangjing/.rvm/gems/ruby-2.0.0-p643@global/gems/cocoapods-1.1.1/lib/cocoapods/installer/analyzer.rb:66:in `analyze'
/Users/huangjing/.rvm/gems/ruby-2.0.0-p643@global/gems/cocoapods-1.1.1/lib/cocoapods/installer.rb:236:in `analyze'
/Users/huangjing/.rvm/gems/ruby-2.0.0-p643@global/gems/cocoapods-1.1.1/lib/cocoapods/installer.rb:150:in `block in resolve_dependencies'
/Users/huangjing/.rvm/gems/ruby-2.0.0-p643@global/gems/cocoapods-1.1.1/lib/cocoapods/user_interface.rb:64:in `section'
/Users/huangjing/.rvm/gems/ruby-2.0.0-p643@global/gems/cocoapods-1.1.1/lib/cocoapods/installer.rb:149:in `resolve_dependencies'
/Users/huangjing/.rvm/gems/ruby-2.0.0-p643@global/gems/cocoapods-1.1.1/lib/cocoapods/installer.rb:110:in `install!'
/Users/huangjing/.rvm/gems/ruby-2.0.0-p643@global/gems/cocoapods-1.1.1/lib/cocoapods/command/install.rb:37:in `run'
/Users/huangjing/.rvm/gems/ruby-2.0.0-p643@global/gems/claide-1.0.1/lib/claide/command.rb:334:in `run'
/Users/huangjing/.rvm/gems/ruby-2.0.0-p643@global/gems/cocoapods-1.1.1/lib/cocoapods/command.rb:50:in `run'
/Users/huangjing/.rvm/gems/ruby-2.0.0-p643@global/gems/cocoapods-1.1.1/bin/pod:55:in `<top (required)>'
/Users/huangjing/.rvm/rubies/ruby-2.0.0-p643/bin/pod:23:in `load'
/Users/huangjing/.rvm/rubies/ruby-2.0.0-p643/bin/pod:23:in `<main>'
```
解决方法:更新xcodeproj
运行命令：gem update xcodeproj
再次pod install还是报错
错误信息：
ArgumentError - Malformed version number string
/Users/huangjing/.rvm/rubies/ruby-2.0.0-p643/lib/ruby/site_ruby/2.0.0/rubygems/version.rb:209:in `initialize'
/Users/huangjing/.rvm/rubies/ruby-2.0.0-p643/lib/ruby/site_ruby/2.0.0/rubygems/version.rb:200:in `new'
/Users/huangjing/.rvm/rubies/ruby-2.0.0-p643/lib/ruby/site_ruby/2.0.0/rubygems/version.rb:200:in `new'
/Users/huangjing/.rvm/gems/ruby-2.0.0-p643@global/gems/cocoapods-1.1.1/lib/cocoapods/generator/xcconfig/aggregate_xcconfig.rb:110:in `embedded_content_settings'
/Users/huangjing/.rvm/gems/ruby-2.0.0-p643@global/gems/cocoapods-1.1.1/lib/cocoapods/generator/xcconfig/aggregate_xcconfig.rb:63:in `generate'
/Users/huangjing/.rvm/gems/ruby-2.0.0-p643@global/gems/cocoapods-1.1.1/lib/cocoapods/generator/xcconfig/aggregate_xcconfig.rb:39:in `save_as'
/Users/huangjing/.rvm/gems/ruby-2.0.0-p643@global/gems/cocoapods-1.1.1/lib/cocoapods/installer/xcode/pods_project_generator/aggregate_target_installer.rb:87:in `block in create_xcconfig_file'
/Users/huangjing/.rvm/gems/ruby-2.0.0-p643@global/gems/cocoapods-1.1.1/lib/cocoapods/installer/xcode/pods_project_generator/aggregate_target_installer.rb:84:in `each'
/Users/huangjing/.rvm/gems/ruby-2.0.0-p643@global/gems/cocoapods-1.1.1/lib/cocoapods/installer/xcode/pods_project_generator/aggregate_target_installer.rb:84:in `create_xcconfig_file'
/Users/huangjing/.rvm/gems/ruby-2.0.0-p643@global/gems/cocoapods-1.1.1/lib/cocoapods/installer/xcode/pods_project_generator/aggregate_target_installer.rb:18:in `block in install!'
/Users/huangjing/.rvm/gems/ruby-2.0.0-p643@global/gems/cocoapods-1.1.1/lib/cocoapods/user_interface.rb:142:in `message'
/Users/huangjing/.rvm/gems/ruby-2.0.0-p643@global/gems/cocoapods-1.1.1/lib/cocoapods/installer/xcode/pods_project_generator/aggregate_target_installer.rb:14:in `install!'
/Users/huangjing/.rvm/gems/ruby-2.0.0-p643@global/gems/cocoapods-1.1.1/lib/cocoapods/installer/xcode/pods_project_generator.rb:160:in `block (2 levels) in install_libraries'
/Users/huangjing/.rvm/gems/ruby-2.0.0-p643@global/gems/cocoapods-1.1.1/lib/cocoapods/installer/xcode/pods_project_generator.rb:158:in `each'
/Users/huangjing/.rvm/gems/ruby-2.0.0-p643@global/gems/cocoapods-1.1.1/lib/cocoapods/installer/xcode/pods_project_generator.rb:158:in `block in install_libraries'
/Users/huangjing/.rvm/gems/ruby-2.0.0-p643@global/gems/cocoapods-1.1.1/lib/cocoapods/user_interface.rb:142:in `message'
/Users/huangjing/.rvm/gems/ruby-2.0.0-p643@global/gems/cocoapods-1.1.1/lib/cocoapods/installer/xcode/pods_project_generator.rb:152:in `install_libraries'
/Users/huangjing/.rvm/gems/ruby-2.0.0-p643@global/gems/cocoapods-1.1.1/lib/cocoapods/installer/xcode/pods_project_generator.rb:64:in `generate!'
/Users/huangjing/.rvm/gems/ruby-2.0.0-p643@global/gems/cocoapods-1.1.1/lib/cocoapods/installer.rb:179:in `block in generate_pods_project'
/Users/huangjing/.rvm/gems/ruby-2.0.0-p643@global/gems/cocoapods-1.1.1/lib/cocoapods/user_interface.rb:64:in `section'
/Users/huangjing/.rvm/gems/ruby-2.0.0-p643@global/gems/cocoapods-1.1.1/lib/cocoapods/installer.rb:178:in `generate_pods_project'
/Users/huangjing/.rvm/gems/ruby-2.0.0-p643@global/gems/cocoapods-1.1.1/lib/cocoapods/installer.rb:115:in `install!'
/Users/huangjing/.rvm/gems/ruby-2.0.0-p643@global/gems/cocoapods-1.1.1/lib/cocoapods/command/install.rb:37:in `run'
/Users/huangjing/.rvm/gems/ruby-2.0.0-p643/gems/claide-1.0.2/lib/claide/command.rb:334:in `run'
/Users/huangjing/.rvm/gems/ruby-2.0.0-p643@global/gems/cocoapods-1.1.1/lib/cocoapods/command.rb:50:in `run'
/Users/huangjing/.rvm/gems/ruby-2.0.0-p643@global/gems/cocoapods-1.1.1/bin/pod:55:in `<top (required)>'
/Users/huangjing/.rvm/rubies/ruby-2.0.0-p643/bin/pod:23:in `load'
/Users/huangjing/.rvm/rubies/ruby-2.0.0-p643/bin/pod:23:in `<main>'
然后查看ruby版本
rvm list known
列表里最新版本只到2.2（最新2.6.0） 并提示rvm版本落后于最新版本
于是更新rvm版本
curl -L get.rvm.io | bash -s stable
再次查看ruby版本
rvm list known
查找结果如下
# MRI Rubies
[ruby-]1.8.6[-p420]
[ruby-]1.8.7[-head] # security released on head
[ruby-]1.9.1[-p431]
[ruby-]1.9.2[-p330]
[ruby-]1.9.3[-p551]
[ruby-]2.0.0[-p648]
[ruby-]2.1[.10]
[ruby-]2.2[.10]
[ruby-]2.3[.7]
[ruby-]2.4[.4]
[ruby-]2.5[.1]
[ruby-]2.6[.0-preview2]
ruby-head
# for forks use: rvm install ruby-head-<name> --url https://github.com/github/ruby.git --branch 2.2
# JRuby
jruby-1.6[.8]
jruby-1.7[.27]
jruby-9.1[.17.0]
jruby[-9.2.0.0]
jruby-head
# Rubinius
rbx-1[.4.3]
rbx-2.3[.0]
rbx-2.4[.1]
rbx-2[.5.8]
rbx-3[.100]
rbx-head
# TruffleRuby
truffleruby[-1.0.0-rc2]
# Opal
opal
# Minimalistic ruby implementation - ISO 30170:2012
mruby-1.0.0
mruby-1.1.0
mruby-1.2.0
mruby-1.3.0
mruby-1[.4.0]
mruby[-head]
# Ruby Enterprise Edition
ree-1.8.6
ree[-1.8.7][-2012.02]
# Topaz
topaz
# MagLev
maglev-1.0.0
maglev-1.1[RC1]
maglev[-1.2Alpha4]
maglev-head
# Mac OS X Snow Leopard Or Newer
macruby-0.10
macruby-0.11
macruby[-0.12]
macruby-nightly
macruby-head
# IronRuby
ironruby[-1.1.3]
ironruby-head
xcode-select: error: tool 'xcodebuild' requires Xcode, but active developer directory '/Library/Developer/CommandLineTools' is a command line tools instance
安装多个xcode后删除原xcodebuild的路径导致pod install失败
解决方案：
sudo gem uninstall cocoapods
