2023更新：新的系统升级后也适用本文的方法
本文内容适合 macOS Bigsur 系统版本升级后，我自己新买的电脑也是用这个方法来安装开发者工具。
问题表现
升级了 macOS Sierria 后，一直用起来非常舒畅。但今天想更新一下项目代码库时突然告诉我说：
Shinys-MacBook-Pro:~ shinyzhu$ svn
xcrun: error: invalid active developer path (/Library/Developer/CommandLineTools), missing xcrun at: /Library/Developer/CommandLineTools/usr/bin/xcrun
如图：
修复步骤
这个问题的原因是升级系统后，命令行工具被干掉了（我就说怎么原来剩余空间一直报警，现在有24G剩余空间了）
修复方式很简单，在命令行输入：
Shinys-MacBook-Pro:~ shinyzhu$ xcode-select --install
会出现一个对话框，选择下载就会为你下载命令行工具了，如图：
等待完成即可使用svn，git了：
Shinys-MacBook-Pro:MCP shinyzhu$ svn status
svn: E155036: Please see the 'svn upgrade' command
svn: E155036: The working copy at '/Users/shinyzhu/Projects/MCP'
is too old (format 29) to work with client version '1.9.4 (r1740329)' (expects format 31). You need to upgrade the working copy first.
Shinys-MacBook-Pro:MCP shinyzhu$ svn upgrade
Upgraded '.'
Shinys-MacBook-Pro:MCP shinyzhu$ svn status
svn需要来一次svn upgrade升级版本。
注：xcode-select —install 只是安装命令行工具，不会安装 xcode
注2：以下内容说明什么是
xcode-select
This package enables UNIX-style development via Terminal by installing command line developer tools, as well as macOS SDK frameworks and headers. Many useful tools are included, such as the Apple LLVM compiler, linker, and Make. If you use Xcode, these tools are also embedded within the Xcode IDE.
Note: macOS comes bundled with xcode-select, a command-line tool that is installed in /usr/bin. It allows you to manage the active developer directory for Xcode and other BSD development tools. See its man page for more information.
Last modified on October 31, 2023