require 'rubygems'
require 'rest-client'
require 'json'

scheme="https"
hostname="yourdomain.com/api/v3"
username="myuser"
password="supersecure"

file = "foo.txt"
payload = nil
File.open(file, "r") do |f|
  payload = {
    :description => "test",
    :public => false,
    :files => {
      "foo.txt" => {
        :content => f.read
      }
    }
  }
end

RestClient.post("#{scheme}://#{username}:#{password}@#{hostname}/gists", payload.to_json, :content_type => "text/json")