title: What is the second parameter/argument to CSV.open( ) in ruby?
body: <p>I think I'm missing something really obvious here, but what is the second argument that everyone puts in for CSV.open method, in this case its 'wb', I've seen other letter(s) put here, but no one really explains what it does. What does it do?</p>
  
  <pre><code>CSV.open("path/to/file.csv", "wb") do |csv|
    csv &lt;&lt; ["row", "of", "CSV", "data"]
    csv &lt;&lt; ["another", "row"]
    # ...
  end
  </code></pre>
  
  <p>The ruby doc doesn't seem to give any explanation. <a href="http://www.ruby-doc.org/stdlib-2.0/libdoc/csv/rdoc/CSV.html">http://www.ruby-doc.org/stdlib-2.0/libdoc/csv/rdoc/CSV.html</a></p>
  
  <p>Thanks!</p>