Ruby - nokogiri, open-uri - Fail to parse page [closed] - ruby

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This code work on some pages, like klix.ba, but cant figure out why it doesn't work for others.
There is no error to explain what went wrong, nothing.
If puts page works, which means I can target the page, and parse it, why I cant get single elements?
require 'nokogiri'
require 'open-uri'
url = 'http://www.olx.ba/'
user_agent = "Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.0.7) Gecko/2009021910 Firefox/3.0.7"
page = Nokogiri::XML(open(url,'User-Agent' => user_agent), nil, "UTF-8")
#puts page - This line work
puts page.xpath('a')

Answer 1

First of all, why are you parsing it as XML?
The following should be correct, considering your page is a HTML website:
page = Nokogiri::HTML(open(url,'User-Agent' => user_agent), nil, "UTF-8")
Furthermore, if you want to strip out all the links (a-tags), this is how:
page.css('a').each do |element|
puts element
end

Answer 2

If you are want to parse content from a web page you need to do this:
require 'nokogiri'
require 'open-uri'
url = 'http://www.olx.ba/'
user_agent = "Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.0.7) Gecko/2009021910 Firefox/3.0.7"
page = Nokogiri::HTML(open(url,'User-Agent' => user_agent), nil, "UTF-8")
#puts page - This line work
puts page.xpath('a')
Here take a look at the Nokogiri documentation
One thing I would suggest is to use a debugger break point in your code (probably after assigning page). Look at the Pry-debugger gem.
So I would do something like this:
require 'nokogiri'
require 'open-uri'
require 'pry' # require the necessary library
url = 'http://www.olx.ba/'
user_agent = "Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.0.7) Gecko/2009021910 Firefox/3.0.7"
page = Nokogiri::HTML(open(url,'User-Agent' => user_agent), nil, "UTF-8")
binding.pry # stop a moment in time in you code (break point)
#puts page - This line work
puts page.xpath('a')