How ruby `require` really work? - ruby

Question

I'm using Archlinux, the ruby location was on /usr/bin/ruby
$ ruby --version
ruby 2.0.0p247 (2013-06-27 revision 41674) [i686-linux]
$ gem install ffi
Building native extensions. This could take a while...
Successfully installed ffi-1.9.0
Parsing documentation for ffi-1.9.0
Done installing documentation for ffi after 41 seconds
1 gem installed
I was using G-WAN to execute a ruby script, but when i use require 'ffi' this output shown:
/usr/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:45:in `require': cannot load such file -- ffi (LoadError)
from /usr/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:45:in `require'
from /home/asd/bin/gwan_linux32-bit/127.0.0.1_8081/#127.0.0.1/csp/test.rb:1:in `<main>'
and require '/home/asd/.gem/ruby/2.0.0/gems/ffi-1.9.0/lib/ffi.rb' shows:
/usr/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:45:in `require': cannot load such file -- ffi_c (LoadError)
from /usr/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:45:in `require'
from /home/asd/.gem/ruby/2.0.0/gems/ffi-1.9.0/lib/ffi.rb:14:in `rescue in <top (required)>'
from /home/asd/.gem/ruby/2.0.0/gems/ffi-1.9.0/lib/ffi.rb:3:in `<top (required)>'
from /usr/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:45:in `require'
from /usr/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:45:in `require'
from /home/asd/bin/gwan_linux32-bit/127.0.0.1_8081/#127.0.0.1/csp/test.rb:21:in `<main>'
the output of p $LOAD_PATH was:
["/usr/lib/ruby/site_ruby/2.0.0" # doesn't exists
, "/usr/lib/ruby/site_ruby/2.0.0/i686-linux" # doesn't exists
, "/usr/lib/ruby/site_ruby" # doesn't exists
, "/usr/lib/ruby/vendor_ruby/2.0.0" # doesn't exists
, "/usr/lib/ruby/vendor_ruby/2.0.0/i686-linux" # doesn't exists
, "/usr/lib/ruby/vendor_ruby" # doesn't exists
, "/usr/lib/ruby/2.0.0"
, "/usr/lib/ruby/2.0.0/i686-linux"
]
the location for FFI was:
$ locate ffi.rb
/home/asd/.gem/ruby/2.0.0/gems/ffi-1.9.0/lib/ffi.rb
/home/asd/.gem/ruby/2.0.0/gems/ffi-1.9.0/lib/ffi/ffi.rb
/opt/jruby/lib/ruby/shared/ffi.rb
/opt/jruby/lib/ruby/shared/ffi/ffi.rb
/opt/jruby/samples/ffi/ffi.rb
so i tried to add the directory to $LOAD_PATH
$LOAD_PATH.unshift '/home/asd/.gem/ruby/2.0.0/gems/ffi-1.9.0/lib'
and now require 'ffi' shows no error..
if i already have many gems installed on ~/.gem/ruby/2.0.0/gems
$ ll ~/.gem/ruby/2.0.0/gems/ | wc
285 2558 17502
what is the correct way to use the gem? is it by adding each path to $LOAD_PATH

Answer 1

This is clearly a Ruby configuration issue, and the suggested RVM tool seems to address it:
RVM is a command-line tool which allows you to easily install, manage,
and work with multiple ruby environments from interpreters to sets of
gems.
As suggested by 'icktoofay', G-WAN could add support for RVM, but I am not sure that it makes sense unless RVM becomes more mainstream than Ruby itself (or assimilated by Ruby).
Now, Jesly Varghese also told us (above) that the issue comes from the fact "you are using system ruby, and calling a gem in user dir".
Did you try to install G-WAN under /opt/gwan ?
Then, this PATH issue may be gone.