为什么 ruby 找不到 'dimensions' gem？

Question

我使用 Jekyll 生成我的博客已经有一段时间了 (source)。今天，在生成过程中没有改变任何东西，我得到了

[...]
jekyll build --config _config_prod.yml
Configuration file: _config_prod.yml
/home/moose/GitHub/MartinThoma.github.io/_plugins/caption_tag.rb:23:in `require': cannot load such file -- dimensions (LoadError)
    from /home/moose/GitHub/MartinThoma.github.io/_plugins/caption_tag.rb:23:in `<top (required)>'
    from /var/lib/gems/2.1.0/gems/jekyll-2.5.3/lib/jekyll/plugin_manager.rb:74:in `require'
    from /var/lib/gems/2.1.0/gems/jekyll-2.5.3/lib/jekyll/plugin_manager.rb:74:in `block (2 levels) in require_plugin_files'
    from /var/lib/gems/2.1.0/gems/jekyll-2.5.3/lib/jekyll/plugin_manager.rb:73:in `each'
    from /var/lib/gems/2.1.0/gems/jekyll-2.5.3/lib/jekyll/plugin_manager.rb:73:in `block in require_plugin_files'
    from /var/lib/gems/2.1.0/gems/jekyll-2.5.3/lib/jekyll/plugin_manager.rb:72:in `each'
    from /var/lib/gems/2.1.0/gems/jekyll-2.5.3/lib/jekyll/plugin_manager.rb:72:in `require_plugin_files'
    from /var/lib/gems/2.1.0/gems/jekyll-2.5.3/lib/jekyll/plugin_manager.rb:18:in `conscientious_require'
    from /var/lib/gems/2.1.0/gems/jekyll-2.5.3/lib/jekyll/site.rb:79:in `setup'
    from /var/lib/gems/2.1.0/gems/jekyll-2.5.3/lib/jekyll/site.rb:41:in `initialize'
    from /var/lib/gems/2.1.0/gems/jekyll-2.5.3/lib/jekyll/commands/build.rb:29:in `new'
    from /var/lib/gems/2.1.0/gems/jekyll-2.5.3/lib/jekyll/commands/build.rb:29:in `process'
    from /var/lib/gems/2.1.0/gems/jekyll-2.5.3/lib/jekyll/commands/build.rb:18:in `block (2 levels) in init_with_program'
    from /usr/lib/ruby/vendor_ruby/mercenary/command.rb:220:in `call'
    from /usr/lib/ruby/vendor_ruby/mercenary/command.rb:220:in `block in execute'
    from /usr/lib/ruby/vendor_ruby/mercenary/command.rb:220:in `each'
    from /usr/lib/ruby/vendor_ruby/mercenary/command.rb:220:in `execute'
    from /usr/lib/ruby/vendor_ruby/mercenary/program.rb:42:in `go'
    from /usr/lib/ruby/vendor_ruby/mercenary.rb:19:in `program'
    from /var/lib/gems/2.1.0/gems/jekyll-2.5.3/bin/jekyll:20:in `<top (required)>'
    from /usr/local/bin/jekyll:23:in `load'
    from /usr/local/bin/jekyll:23:in `<main>'
Makefile:35: recipe for target 'deploy' failed
make: *** [deploy] Error 1

我不是 Ruby 开发人员，但我猜问题是 require 'dimensions'？但是，当我在 irb 中执行这一行时，它只显示 => true.

这是什么问题，我该如何解决？

诊断信息

$ jekyll --version
jekyll 2.5.3
$  head -1 `which irb` 
#!/usr/bin/ruby2.1
$  head -1 `which jekyll`
#!/usr/bin/ruby2.1

在 irb 中执行 RUBY_VERSION 得到 => "2.1.5".

Answer 1

已通过将 gem 'dimensions' 添加到文件 Gemfile 来解决问题。现在看起来像这样：

source "https://rubygems.org"

# see https://github.com/paulrobertlloyd/paulrobertlloyd.com/blob/master/Gemfile
# Guard (automates development tasks)

# Jekyll (generates static files)
gem 'jekyll'
group :jekyll_plugins do
  gem 'jekyll-paginate'
  gem 'dimensions'
  gem 'rmagick'
end

# Rake (manages build tasks)
gem 'rake'

为什么 ruby 找不到 'dimensions' gem？

Why doesn't ruby find the 'dimensions' gem?

ruby

jekyll

诊断信息