A very simple Ruby wrapper for PhantomJS.

exporter.rb

# exporter.rb
# A very simple Ruby wrapper for PhantomJS
# for create PDF's or anything you can create with PhantomJS
require 'json'

class Exporter
  class PhantomJSNotFound < StandardError; end

  class << self
    def default_options
      {
        format: 'A4',
        orientation: 'portrait',
        border: '1cm',
        rasterize_bin: File.dirname(__FILE__) + '/rasterize.js',
        phantomjs_bin: Exporter.phantomjs_bin,
        timeout: 1000,
        headers: nil
      }
    end

    def phantomjs_bin
      bin_path = (`which phantomjs`).to_s.chomp
      raise Exporter::PhantomJSNotFound if bin_path.empty?
      bin_path
    end
  end

  def initialize(url, output, options = {})
    @url             = url
    @output          = output
    @default_options = Exporter.default_options.merge(options)
    execute
  end

  def file_path
    @output
  end

  def file
    File.open(@output)
  end

  private

  def execute
    cmd  = @default_options[:phantomjs_bin]
    cmd += " #{@default_options[:rasterize_bin]}"
    cmd += " --url=#{@url}"
    cmd += " --output=#{@output}"
    cmd += " --format=#{@default_options[:format]}"
    cmd += " --orientation=#{@default_options[:orientation]}"
    cmd += " --border=#{@default_options[:border]}"
    cmd += " --timeout=#{@default_options[:timeout]}"
    cmd += " --headers='#{@default_options[:headers].to_json}'" unless @default_options[:headers].nil?
    `#{cmd}`
  end
end

rasterize.js

var system = require('system')
  , page   = require('webpage').create()
  , args   = {};

if( system.args.length > 1 ){
  for( var i = 1; i < system.args.length; i++ ){
    var params = system.args[i].split('='),
        key    = params[0].replace('--', ''),
        value  = params[1];

    if( key == 'headers' ){
      args[key] = JSON.parse(value);
    }else{
      args[key] = value;
    }
  }
}

page.paperSize = {
  format: args.format,
  orientation: args.orientation,
  border: args.border
};

if( args.hasOwnProperty('headers') ){
  page.customHeaders = args.headers;
}

page.open(args.url, function (status) {
  if(status !== 'success') {
    console.log('Unable to access the network!');
    phantom.exit(1);
  }else{    
    setTimeout(function(){
      page.render(args.output);
      phantom.exit();
    }, args.timeout);
  }
});

Node.JS is required, after installed it, proceed with the installation of PhantomJS:

npm install -g phantomjs

Then from Ruby, in this case a Rails controller:

def export
  pdf = Exporter.new('http://google.cl', '/home/user/google.pdf')
  send_file(pdf.file_path, filename: 'Google', type: 'application/pdf', disposition: 'inline')
end