homebrew - "brew link"有什么作用？

Question

当我运行 brew doctor 时，我收到常见警告:

Warning: You have unlinked kegs in your Cellar
Leaving kegs unlinked can lead to build-trouble and cause brews that depend on
those kegs to fail to run properly once built. Run `brew link` on these:
# [...]

小桶取消链接意味着什么？ brew link 到底是做什么的？

Answer 1

Homebrew 可以允许安装公式的多个版本。例如，有名为 node 和 node@10 及类似公式。

$ brew info node@10
...
==> Caveats
node@10 is keg-only, which means it was not symlinked into /usr/local,
because this is an alternate version of another formula.

如果我同时安装了 node 和 node@10，其中 node 版本为 v11。我可以稍后决定使用 brew link 激活早期版本:

$ brew unlink node

$ brew link node@10

$ cd /urs/local/bin
$ ls -l node
lrwxr-xr-x  1 user  admin  34 12 Dec 20:07 node -> ../Cellar/node@10/10.14.1/bin/node

这里的符号链接(symbolic link)node指向安装在Cellar中的早期版本(keg-only)。