Only use environment variables to select the desired ruby

[postmodern]

Specifying the desired ruby in the first argument is not compatible with systems that do not have rubypick installed. Additionally, if the ruby process runs system('ruby',...) it will lose the selected ruby:

$ ruby _jruby_ -S irb
irb(main):001:0> system 'ruby', '-v'
ruby 2.0.0p353 (2013-11-22 revision 43784) [x86_64-linux]
=> true

rubypick should only support using the RUBYPICK env variable.

[voxik]

I am not sure what is your objection or use case. Could you please elaborate?

[postmodern]

My objection is a user's choice of ruby via ruby _jruby_ is not persisted by system('ruby',...). Were as RUBYPICK=jruby ruby ... does get persisted, since child processes inherit their parent's environment variables. This leads to confusing / surprising behavior when jruby processes accidentally spawn MRI sub-processes.

[voxik]

I don't think there is satisfiable solution. If you would run:

$ jruby -S irb
irb(main):001:0> system 'ruby', '-v'
ruby 2.0.0p353 (2013-11-22 revision 43784) [x86_64-linux]

Is this expected? You get what you are asking for.

We could go the other way around, i.e. when specifying the interpreter by parameter, define the environment variable, but somebody could object this approach as well.