我有一个Ruby脚本，它试图要求restclient模块。当我把它缩减到这一行时，它仍然失败：

#!/usr/bin/env ruby

require 'restclient'

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当我运行它时，我得到以下错误：

./test.rb:3:in `require': no such file to load -- restclient (LoadError)
    from ./test2.rb:3

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当我运行irb时，模块加载正常：

$ irb
>> require "restclient"
=> true
>>

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据我所知，脚本和irb看起来都有相同的模块路径：

$ ruby -e "puts $:"
/Library/Ruby/Site/1.8
/Library/Ruby/Site/1.8/powerpc-darwin10.0
/Library/Ruby/Site/1.8/universal-darwin10.0
/Library/Ruby/Site
/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/vendor_ruby/1.8
/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/vendor_ruby/1.8/universal-darwin10.0
/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/vendor_ruby
/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8
/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/powerpc-darwin10.0
/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/universal-darwin10.0
.

$ irb
>> puts $:
/Library/Ruby/Site/1.8
/Library/Ruby/Site/1.8/powerpc-darwin10.0
/Library/Ruby/Site/1.8/universal-darwin10.0
/Library/Ruby/Site
/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/vendor_ruby/1.8
/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/vendor_ruby/1.8/universal-darwin10.0
/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/vendor_ruby
/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8
/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/powerpc-darwin10.0
/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/universal-darwin10.0
.
=> nil
>>

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什么会导致一个模块通过irb加载，而不是直接通过Ruby运行？
另一个令人困惑的细节是，restclient gem似乎并不在我的开发之路上，irb是如何找到它的？

$ locate restclient | grep gems
/Library/Ruby/Gems/1.8/gems/rest-client-1.6.1/bin/restclient
/Library/Ruby/Gems/1.8/gems/rest-client-1.6.1/lib/restclient
/Library/Ruby/Gems/1.8/gems/rest-client-1.6.1/lib/restclient/abstract_response.rb
/Library/Ruby/Gems/1.8/gems/rest-client-1.6.1/lib/restclient/exceptions.rb
/Library/Ruby/Gems/1.8/gems/rest-client-1.6.1/lib/restclient/net_http_ext.rb
/Library/Ruby/Gems/1.8/gems/rest-client-1.6.1/lib/restclient/payload.rb
/Library/Ruby/Gems/1.8/gems/rest-client-1.6.1/lib/restclient/raw_response.rb
/Library/Ruby/Gems/1.8/gems/rest-client-1.6.1/lib/restclient/request.rb
/Library/Ruby/Gems/1.8/gems/rest-client-1.6.1/lib/restclient/resource.rb
/Library/Ruby/Gems/1.8/gems/rest-client-1.6.1/lib/restclient/response.rb
/Library/Ruby/Gems/1.8/gems/rest-client-1.6.1/lib/restclient.rb
/Library/Ruby/Gems/1.8/gems/rest-client-1.6.1/spec/restclient_spec.rb

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