A very concise AWS S3 uploader example in Ruby

require "rubygems"
require 'sinatra'
require "aws/s3"

get '/' do
 return %Q{
 <form action="upload" method="post" accept-charset="utf-8" enctype="multipart/form-data">
 <div>
 <input type="file" name="file" value="" id="file">
 </div>
 <div>
 <input type="submit" value="Upload &uarr;">
 </div>
 </form>
 }
end

post '/upload' do
 awskey = 'mykey'
 awssecret = 'mysecret'
 bucket = 'mybucket'
 file = params[:file][:tempfile]
 filename = params[:file][:filename]
 AWS::S3::Base.establish_connection!(
 :access_key_id => awskey,
 :secret_access_key => awssecret
 )
 AWS::S3::S3Object.store(
 filename,
 open(file.path),
 bucket,
 :access => :public_read
 )
 url = "https://#{bucket}.s3.amazonaws.com/#{filename}"
 return url
end