xcode路径的改变导致的cocoapods编译失败或者xcrun: error: active developer path ("/Applications/Xcode.app/Contents/D

这几天心血来潮，更新了下Mac系统，然后装了下Xcode10装逼，（原先Xcode9.0是同事下载，为了省时间直接通过隔空投送传过来的）接下来就懵逼了。
接着我就直接熟练的使用cocoapods（10.0的Xcode要升级系统，对应的cocoapods一定要升级，不然也无法使用cocoapods），巴拉巴拉巴拉然后再 pod install，接下来就懵逼了。。。。
报如下错误:

Setting up CocoaPods master repo
$ /usr/bin/git remote set-url origin https://github.com/CocoaPods/Specs.git
xcrun: error: active developer path ("/Applications/Xcode.app/Contents/Developer") does not exist, use xcode-select --switch path/to/Xcode.app to specify the Xcode that you wish to use for command line developer tools (or see man xcode-select)
[!] Failed: /usr/bin/git remote set-url origin https://github.com/CocoaPods/Specs.git
$ /usr/bin/git checkout master
xcrun: error: active developer path ("/Applications/Xcode.app/Contents/Developer") does not exist, use xcode-select --switch path/to/Xcode.app to specify the Xcode that you wish to use for command line developer tools (or see man xcode-select)
[!] Failed: /usr/bin/git checkout master
[!] Unable to add a source with url https://github.com/CocoaPods/Specs.git named master-1.
(The master repo is not a git repo.)
You can try adding it manually in ~/.cocoapods/repos or via pod repo add.
试了几次都不行，又换pod update还是不行，于是我开始怀疑是不是COcoaPods炸了，还是我升级了系统之后炸了。。。。想想不科学，应该是XCode的问题，仔细阅读错误（原谅我英文差），貌似看懂了那么一点，可能是我删了XCode又恢复导致的。就这么一百度果然还真是的。
一句命令搞定：sudo xcode-select --switch /Applications/Xcode.app（后面的地址直接打开程序把Xcode往这里拖即可)。完事后再pod install。。biubiubiu出现了熟悉的“Analyzing dependencies”字样，最后提示“Pod installation complete! There are 15 dependencies from the Podfile and 16 total pods installed.”。ok成功了。
以上记录我遇到的坑爹错误，给初次遇到这样问题的童鞋一点思路，不至于搓手不急（当时CocoaPods不能用我心中一万个草泥马崩腾啊）