2021年方案(使用rvm):

如果您在终端中输入哪种ruby，并显示/usr/bin/ruby，您可以尝试此解决方案。

安装区 curl -L https://get.rvm.io | bash -s稳定 使用RVM安装ruby RVM安装ruby-3.0.0 使用您安装的ruby版本 RVM使用ruby-3.0.0 再次输入哪个ruby，这将显示/Users/mac_user_name/.rvm/ ruby /ruby-3.0.0/bin/ruby。 这是使用ruby的新途径。

对我来说，问题是由于使用rbenv，忘记全局设置正确的版本。

所以我必须用rbenv global xxx来设置它

在我的情况下，我安装了2.0.0-p247，所以我必须发出命令:

rbenv global 2.0.0-p247
rbenv rehash

然后一切都运转正常。

在MacOS Mojave上成功测试:

卸载所有旧的ruby版本(假设你有2.00和2.3.0): $ RVM卸载2.0.0 $ RVM卸载2.3.0 安装全新的ruby版本: 安装ruby 设置默认别名为您的版本: $ RVM别名创建默认ruby 重新启动您的系统，因为这是您的计算机加载最新安装的新ruby版本的最安全的方式。

完成以上步骤后，您可以成功地运行任何gem命令。

正如bobbdelsol所指出的，rehash对我来说很管用:

==> which ruby
/usr/bin/ruby

==> rbenv install 1.9.3-p551
Downloading ruby-1.9.3-p551.tar.bz2...
-> https://cache.ruby-lang.org/pub/ruby/1.9/ruby-1.9.3-p551.tar.bz2
Installing ruby-1.9.3-p551...
Installed ruby-1.9.3-p551 to /Users/username/.rbenv/versions/1.9.3-p551


==> which ruby
/Users/username/.rbenv/shims/ruby

==> which gem
/Users/username/.rbenv/shims/gem

==> gem install compass
ERROR:  While executing gem ... (Gem::FilePermissionError)
    You don't have write permissions for the /Library/Ruby/Gems/2.0.0 directory.


==> ruby -v
ruby 2.0.0p648 (2015-12-16 revision 53162) [universal.x86_64-darwin15]


==> rbenv global 1.9.3-p551


==> ruby -v
ruby 2.0.0p648 (2015-12-16 revision 53162) [universal.x86_64-darwin15]


==> rbenv global 1.9.3-p551


==> rbenv rehash


==> ruby -v
ruby 1.9.3p551 (2014-11-13 revision 48407) [x86_64-darwin15.4.0]


==> gem install compass
Fetching: sass-3.4.22.gem (100%)
Fetching: multi_json-1.11.3.gem (100%)
Fetching: compass-core-1.0.3.gem (100%)
Fetching: compass-import-once-1.0.5.gem (100%)
Fetching: chunky_png-1.3.5.gem (100%)
Fetching: rb-fsevent-0.9.7.gem (100%)
Fetching: ffi-1.9.10.gem (100%)
Building native extensions.  This could take a while...
Fetching: rb-inotify-0.9.7.gem (100%)
Fetching: compass-1.0.3.gem (100%)
    Compass is charityware. If you love it, please donate on our behalf at http://umdf.org/compass Thanks!
Successfully installed sass-3.4.22
Successfully installed multi_json-1.11.3
Successfully installed compass-core-1.0.3
Successfully installed compass-import-once-1.0.5
Successfully installed chunky_png-1.3.5
Successfully installed rb-fsevent-0.9.7
Successfully installed ffi-1.9.10
Successfully installed rb-inotify-0.9.7
Successfully installed compass-1.0.3
9 gems installed
Installing ri documentation for sass-3.4.22...
Installing ri documentation for multi_json-1.11.3...
Installing ri documentation for compass-core-1.0.3...
Installing ri documentation for compass-import-once-1.0.5...
Installing ri documentation for chunky_png-1.3.5...
Installing ri documentation for rb-fsevent-0.9.7...
Installing ri documentation for ffi-1.9.10...
Installing ri documentation for rb-inotify-0.9.7...
Installing ri documentation for compass-1.0.3...
Installing RDoc documentation for sass-3.4.22...
Installing RDoc documentation for multi_json-1.11.3...
Installing RDoc documentation for compass-core-1.0.3...
Installing RDoc documentation for compass-import-once-1.0.5...
Installing RDoc documentation for chunky_png-1.3.5...
Installing RDoc documentation for rb-fsevent-0.9.7...
Installing RDoc documentation for ffi-1.9.10...
Installing RDoc documentation for rb-inotify-0.9.7...
Installing RDoc documentation for compass-1.0.3...

我对我的Mac进行了格式化，许多建议的解决方案对我不起作用。 对我来说有用的是这些正确顺序的命令:

安装自制程序: /usr/bin/ruby -e "$(curl - ssl https://raw.githubusercontent.com/Homebrew/install/master/install)" 安装Ruby: 编译安装ruby 安装指南: 须藤宝石安装指南针

sudo gem update --system
sudo gem install (gemfile)