在Ruby on Rails中使用bundle exec

Question

What does bundle exec rake db:migrate really means? or bundle exec rails s I understand that bundle handle all the gems we specify in our Gemfile,and rake handle all the things which you can do through scripts but these commands don't get executed without prefixing bundle exec and I couldn't find any documentation about this on internet !!

Answer 1

Bundler - The best way to manage your application's dependencies

Run the command in context of the bundle

$ bundle exec

Exec runs a command, providing it access to the gems in the bundle. While using bundle exec you can require and call the bundled gems as if they were installed into the systemwide RubyGems repository

Answer 2

With:

bundle exec rake db:migrate

In an informal way, it means that your rails environment will

-Install dependencies with bundler then -Run your database migrations in your rails app (/yourapp/db/migrate)

Instead of a database operation, you could do any other command line stuff that can be controlled by rake (like building your app, extensions, cleaning some files, etc.)

This can be useful if you want to avoid confusing scenarios where maybe some gems in your setup are outdated, or missing from your environment. It's a good practice because calling rake by itself will not guarantee that you got all your dependencies in check.

Answer 3

Bundler acts to create a somewhat isolated Ruby language programming environment separate from the underlying host system. There are limits to what it can do. For example, you need something like RVM to manage different versions of the Ruby language virtual machine. And of course both Ruby and Bundler itself have to be available outside your project in order to run.

However, within a single project bundle exec will restrict access to gems installed by Bundler into that project. This means that the Rake utility when invoked via bundle exec will be the version of rake installed in your project and not the system-wide version. It also means that `bundle rake db:migrate' will use the correct version of rails installed for your project. This isolates your project from updates done to the Ruby environment on the host and thereby prevents compatibility issues from arising.

You can get around the verbosity by creating aliases in your .bash_profile (assuming you are using OSX or Linux/unix) for bundle exec , bundle exec rake and bundle exec rails . I use bexec, brake and brails.