Mac安装yarn
Mac升级到10.15.4之后，Xcode也升级到Version 11.4.1 (11E503a)，终端下执行 brew install yarn 进行 yarn安装，最后报错gcc错误。
Error: An exception occurred within a child process:
CompilerSelectionError: gcc cannot be built with any available compilers.
Install GNU's GCC:
brew install gcc
一、按照提示安装gcc
既然gcc错误，直接安装gcc
执行 brew install gcc
错误如下：
$ brew install gcc
Updating Homebrew...
Warning: Building gcc from source:
The bottle needs the Xcode CLT to be installed.
xcrun: error: invalid active developer path (/Library/Developer/CommandLineTools), missing xcrun at: /Library/Developer/CommandLineTools/usr/bin/xcrun
Error: An exception occurred within a child process:
CompilerSelectionError: gcc cannot be built with any available compilers.
Install GNU's GCC:
brew install gcc
so,度娘试试看：
原因是 在从App Store上下载Xcode后，默认是不会安装Command Line Tools的.
二、解决gcc错误的方法
更新一下Xcode，终端下执行指令：
xcode-select --install
执行结果如下：
$ xcode-select --install
xcode-select: note: install requested for command line developer tools
三、安装 yarn
$ brew install yarn
Updating Homebrew...
==> Downloading https://yarnpkg.com/downloads/1.22.4/yarn-v1.22.4.tar.gz
==> Downloading from https://github-production-release-asset-2e65be.s3.amazonaws
# 2.8%
curl: (56) LibreSSL SSL_read: SSL_ERROR_SYSCALL, errno 60
Error: An exception occurred within a child process:
DownloadError: Failed to download resource "yarn"
Download failed: https://yarnpkg.com/downloads/1.22.4/yarn-v1.22.4.tar.gz
网速问题，那么，配置VPN吧。
如果没有VPN的话，参考第五步。
四、配置VPN后，再次安装 yarn
$ brew install yarn
Updating Homebrew...
==> Auto-updated Homebrew!
Updated 1 tap (homebrew/core).
==> Updated Formulae
feedgnuplot geoipupdate mariadb repo
fonttools glooctl [email protected]
==> Downloading https://yarnpkg.com/downloads/1.22.4/yarn-v1.22.4.tar.gz
==> Downloading from https://github-production-release-asset-2e65be.s3.amazonaws.com/4997064
######################################################################## 100.0%
🍺 /usr/local/Cellar/yarn/1.22.4: 14 files, 5MB, built in 5 minutes 1 second
五、下载 yarn的 tar.gz包，进行离线安装。
(PS:没有尝试过，暂时不知道是否好用)
1、yarn的 tar.gz包下载地址：
https://yarnpkg.com/downloads/1.22.4/yarn-v1.22.4.tar.gz
2、离线安装参考文章：
https://www.cnblogs.com/luguiqing/p/11553067.html
参考文章：
1、https://www.cnblogs.com/qyf404/p/how_install_gcc_in_mac.html