ruby-on-rails - bundle 和 bundle 更新有什么区别？

Question

使用两个命令 bundle 和 bundle update 时得到两个不同的结果

如果我使用bundle update，我会收到以下错误:

Resolving dependencies...
Bundler could not find compatible versions for gem "railties":
  In Gemfile:
    requirejs-rails (>= 0) ruby depends on
      railties (~> 3.1.1) ruby

    rails (= 4.0.0.rc2) ruby depends on
      railties (4.0.0.rc2)

Bundler could not find compatible versions for gem "rails":
  In Gemfile:
    requirejs-rails (>= 0) ruby depends on
      rails (~> 3.1.1) ruby

    rails (4.0.0.rc2)

但是如果我只使用bundle，我会得到以下结果:

Resolving dependencies...
Bundler could not find compatible versions for gem "activesupport":
  In snapshot (Gemfile.lock):
    activesupport (3.2.2)

  In Gemfile:
    rails (= 4.0.0.rc2) ruby depends on
      activesupport (= 4.0.0.rc2) ruby

Running `bundle update` will rebuild your snapshot from scratch, using only
the gems in your Gemfile, which may resolve the conflict.

这些错误指向两个不同的依赖关系问题，但这两个命令都是从 https://rubygems.org/获取 gem 元数据... 和 解决依赖关系...，那么它们有什么不同呢？

我一直只使用bundle，但尝试bundle update并注意到了差异。

Answer 1

In a nutshell: bundle install handles changes to the Gemfile and bundle update upgrades gems that are already managed by Bundler.

http://viget.com/extend/bundler-best-practices

不用说，bundle 和 bundle install 是同一个命令，install 是 bundle 的默认选项>.