There is a program, like this:

#! /usr/bin/env ruby
#...
require 'getoptlong'
#...


However, the error message given is:
ruby/unix/mkdir.rb:13:in `require': No such file to load -- getoptlong (LoadError)
        from ruby/unix/mkdir.rb:13


I tried to print out the loading paths:

/usr/local/ruby/l.6.8/lib/ruby/site_ruby/1.6
/usr/local/ruby/l.6.8/lib/ruby/site_ruby/1.6/i686-linux
/usr/local/ruby/l.6.8/lib/ruby/site_ruby
/usr/local/ruby/l.6.8/lib/ruby/1.6
/usr/local/ruby/l.6.8/lib/ruby/1.6/i686-linux
..


There seems to be nothing wrong with the loading paths and the getoptlong.rb
is in /usr/local/ruby/l.6.8/lib/ruby/1.6 . Really confused. Can someone expert
help?

Thanks in advance.