2020 10 月 22 日
gem install 时权限问题的修正
进行 gem install 时，如果报如下权限错误：
$ gem install jekyll bundler
gem install jekyll bundler
ERROR: While executing gem ... (Gem::FilePermissionError)
You don't have write permissions for the /Library/Ruby/Gems/2.6.0 directory.
可尝试下面这些解决方式。
--user-install
根据这个回答，似乎加上 --user-install 参数就可以修正：
gem install name_of_gem --user-install
修正 PATH
如果实测发现仍然不行：
$ gem install jekyll bundler --user-install
WARNING: You don't have /Users/wayongliu/.gem/ruby/2.6.0/bin in your PATH,
gem executables will not run.
Building native extensions. This could take a while...
ERROR: Error installing jekyll:
ERROR: Failed to build gem native extension.
…
不过这里的错误信息提示变了，和 PATH 有关，于是根据这个回答，修正一个 PATH：
$ PATH="`ruby -e 'puts Gem.user_dir'`/bin:$PATH"
fish 环境使用如下命令：
$ set PATH "`ruby -e 'puts Gem.user_dir'`/bin:$PATH"
或者添加如下命令到 shell 配置文件中：
set -gx PATH ~/.gem/ruby/2.6.0/bin $PATH
重装 Ruby
如果仍然不行，可以尝试使用 brew 重装 Ruby，抛弃 mac 自带的版本。安装过程输出的信息会有如下提示：
By default, binaries installed by gem will be placed into:
/usr/local/lib/ruby/gems/2.7.0/bin
You may want to add this to your PATH.
ruby is keg-only, which means it was not symlinked into /usr/local,
because macOS already provides this software and installing another version in
parallel can cause all kinds of trouble.
If you need to have ruby first in your PATH run:
echo 'set -g fish_user_paths "/usr/local/opt/ruby/bin" $fish_user_paths' >> ~/.config/fish/config.fish
For compilers to find ruby you may need to set:
set -gx LDFLAGS "-L/usr/local/opt/ruby/lib"
set -gx CPPFLAGS "-I/usr/local/opt/ruby/include"
For pkg-config to find ruby you may need to set:
set -gx PKG_CONFIG_PATH "/usr/local/opt/ruby/lib/pkgconfig"
根据提示，添加相应脚本的 shell 的配置中。
echo 'set -g fish_user_paths "/usr/local/opt/ruby/bin" $fish_user_paths' >> ~/.config/fish/config.fish
刷新配置：
$ source ~/.config/fish/fish.config
然后再执行 gem 安装相关的命令，应该就解决了。
$ gem install --user-install bundler jekyll
Fetching public_suffix-4.0.6.gem
Fetching i18n-1.8.5.gem
Fetching eventmachine-1.2.7.gem
Fetching http_parser.rb-0.6.0.gem
Fetching colorator-1.1.0.gem
Fetching addressable-2.7.0.gem
Fetching concurrent-ruby-1.1.7.gem
Fetching em-websocket-0.5.2.gem
…
检查安装：
$ jekyll -v
jekyll 4.1.1
如果报 jekyll 命令找不到，检查 shell 配置中是 PATH 是否配置正确，见上面步骤。
以上。