Question

This is a simple question, but I cannot seem to find a good answer in the docs (I’m a newbie with RVM).

What is the difference between rvm use ruby-1.9.2-head@rails3 and rvm ruby-1.9.2-head@rails3?

Was trying to setup two versions of my gemsets for 2 projects (rails 3.1 and 3.0.9) and was going to do:

rvm gemset create proj1 proj2
rvm 1.9.2-head@proj1
gem install rails -v 3.1

rvm 1.9.2-head@proj2
gem install rails -v 3.0.9

and then trying to figure out whether to use

rvm 1.9.2-head@proj1 

or

rvm use 1.9.2-head@proj1

to switch to that project/gemset. Hence my question…

Answer 1

AFAIK, the rvm command alone is meant to be used to run something against multiple versions of ruby/ruby gems. For example, you can specify rvm 1.9.2,1.8.7 test.rb and it will execute test.rb using both rubies.

In contrast, rvm use sets up your current shell environment to use whatever ruby you’ve passed. so if you rvm use 1.9.2@proj1, your next ruby command can simply be ruby whatever.rb, and rvm will pick ruby 1.9.2 using your proj1 gem set.

so, to sum it up, use rvm 1.9.2,1.8.7 something.rb when you want to run against multiple rubies, use rvm use 1.9.2 when you want to set the ruby your current shell will use.

EDIT

This would’ve just looked terrible in a comment, so I’m editing instead. My output from those rvm commands looks like:

## RVM use will set the ruby for this shell
[Moe:~]$ rvm use 1.9.2
Using /Users/nunya/.rvm/gems/ruby-1.9.2-p290
[Moe:~]$ ruby -e 'puts `rvm current`'
ruby-1.9.2-p290

## rvm without the use will execute the command with all the rubies passed, 
## but will leave the shells ruby alone.
[Moe:~]$ rvm 1.9.2,1.9.3 -e 'puts `rvm current`'
ruby-1.9.2-p290
ruby-1.9.3-preview1
[Moe:~]$ ruby -e 'puts `rvm current`'
ruby-1.9.2-p290
# with a single ruby:
[Moe:~]$ rvm 1.9.3 -e 'puts `rvm current`'
ruby-1.9.3-preview1
[Moe:~]$ rvm current
ruby-1.9.2-p290