How do I determine which gems, and versions, are necessary for a ruby/ruby-on-rails project?

I have inherited a project and am not sure how to install the project's 'required' gems?

For example,

rake gems:install
rake aborted!
no such file to load -- openssl

I realize that I need openssl, but which version?

Also, how do i determine which other gems i need to install without having to keep re-runing gems:install and getting newest version?

A开发者_如何学Pythonnd this project does not have a Gemfile so I can't use Bundler. :(

if there is a Gemfile, then you could run

bundle

inside your rails app folder and you should get everything required (you have to install bundler first with 'gem install bundler'). if not, you can look in the config/environment.rb which gems are included there.

Try:

bundle list

It may not show you what system dependencies you need, since some Gems ship with native extensions that are built using their own toolchain and often fail at the ./configure or make steps, but it will show you what Gems are needed.

You can also read the Gemfile, though you won't see your dependencies' dependencies that way (unless you have a Gemfile.lock to look at).