.RVM helper tool

Phusion Passenger provides the `passenger-config --ruby-command` tool for figuring out the correct command for invoking a specific Ruby interpreter. This is especially useful for RVM users. Suppose that you have both Ruby 1.8.7 and Ruby 1.9.3 installed through RVM, and you want to know the correct commands for each Ruby interpreter.

For this purpose we'll want to invoke `passenger-config` using its full path, because each time you `rvm use` a different Ruby interpreter, RVM changes `$PATH`. If you did not install Phusion Passenger through the generic tarball installation method, then here's how you can figure out where `passenger-config` is:

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$ which passenger-config
/opt/passenger/bin/passenger-config
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Now, switch to all the RVM Ruby interpreters you want to use. In each interpreter, invoke `passenger-config --ruby-command`. For Ruby 1.8.7:

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$ rvm use 1.8.7
$ /opt/passenger/bin/passenger-config --ruby-command
passenger-config was invoked through the following Ruby interpreter:
  Command: /usr/local/rvm/wrappers/ruby-1.8.7-p358/ruby
  Version: ruby 1.8.7 (2012-02-08 patchlevel 358) [universal-darwin12.0]
  To use in Apache: PassengerRuby /usr/local/rvm/wrappers/ruby-1.8.7-p358/ruby
  To use in Nginx : passenger_ruby /usr/local/rvm/wrappers/ruby-1.8.7-p358/ruby
  To use with Standalone: /usr/local/rvm/wrappers/ruby-1.8.7-p358/ruby /opt/passenger/bin/passenger start


## Notes for RVM users
Do you want to know which command to use for a different Ruby interpreter? 'rvm use' that Ruby interpreter, then re-run 'passenger-config --ruby-command'.
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Then, for Ruby 1.9.3:

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$ rvm use 1.9.3
$ /opt/passenger/bin/passenger-config --ruby-command
passenger-config was invoked through the following Ruby interpreter:
  Command: /usr/local/rvm/wrappers/ruby-1.9.3-p392/ruby
  Version: ruby 1.9.3p392 (2013-02-22 revision 39386) [x86_64-darwin12.2.1]
  To use in Apache: PassengerRuby /usr/local/rvm/wrappers/ruby-1.9.3-p392/ruby
  To use in Nginx : passenger_ruby /usr/local/rvm/wrappers/ruby-1.9.3-p392/ruby
  To use with Standalone: /usr/local/rvm/wrappers/ruby-1.9.3-p392/ruby /opt/passenger/bin/passenger start


## Notes for RVM users
Do you want to know which command to use for a different Ruby interpreter? 'rvm use' that Ruby interpreter, then re-run 'passenger-config --ruby-command'.
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