pod search 一个库，发现怎么也搜不到。是因为pod版本低了。于是更新pod。出现了

Failed to connect to GitHub to update the CocoaPods/Specs specs repo - Please check if you are offline, or that GitHub is down

查到文章https://www.jianshu.com/p/a502eb72b689 上面说要更新openssl

$ which openssl
/usr/bin/openssl

$ openssl version
OpenSSL 0.9.8zh 14 Jan 2016

/usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"

$ brew update

显示

-bash: brew: command not found

做到这步，发现我没安装brew。
执行如下

ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"

报错

curl: (7) Failed to connect to raw.githubusercontent.com port 443: Operation

参考资料1：https://www.jianshu.com/p/68efabd2e32b
2：官网https://brew.sh/index_zh-cn
关掉了蓝灯，重新安装官网提示执行

/usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"

安装成功

brew --version

显示Homebrew 2.1.8
重新$ brew update，却出现了：

Error: Fetching Homebrew
Error: Fetching /usr/local/Homebrew failed!

参考资料：https://www.jianshu.com/p/62f1b963baa6

将源替换过去，又替换回来，重新$ brew update 终于成功了。
然后安文章https://www.jianshu.com/p/a502eb72b689安装OpenSSL