What does bundle exec rake mean?

Question

What does bundle exec rake db:migrate mean? Or just bundle exec rake <command> in general?

I understand that bundle takes care of maintaining things in the Gemfile. I know what the word "exec" means. I understand that rake maintains all the different scripty things you can do, and I know that db:migrate is one of those. I just don't know what all these words are doing together. Why should bundle be used to execute rake to execute a database migrate?

Answer 1

This comes up a lot when your gemfile.lock has different versions of the gems installed on your machine. You may get a warning after running rake (or rspec or others) such as:

You have already activated rake 10.3.1, but your Gemfile requires rake 10.1.0. Prepending "bundle exec" to your command may solve this.

Prepending bundle exec tells the bundler to execute this command regardless of the version differential. There isn't always an issue, however, you might run into problems.

Fortunately, there is a gem that solves this: rubygems-bundler.

$ gem install rubygems-bundler

$ $ gem regenerate_binstubs

Then try your rake, rspec, or whatever again.