Using only Ruby and not the Rails environment : how to upload a file from the local filesystem to a predetermined location in Amazon S3

ruby_upload_s3.rb

#requiring official aws-sdk ruby gem
# stable and widely used : https://github.com/aws/aws-sdk-ruby
# last authored 8 hours from now

require 'aws-sdk'

s3 = AWS::S3.new

s3.config(
        :access_key_id     => ENV['ACCESS_KEY_ID'], #storing access keys on remote server as ENV Variables is a good practice
        :secret_access_key => ENV['SECRET_ACCESS_KEY'] #because comitting keys to code itself is bad security
      )

bucket = s3.buckets.create("foo_upload_bucket") # every S3 bucket has a name | this would be the "predetermined location"
# there are no "predetermined locations" inside a S3 bucket per se like folders
basename = File.basename(file_name)
o = b.objects[basename]
o.write(:file => file_name, :acl => :public_read) # acl is access control parameter - we can change it to private