How I can copy to the clipboard the path (or the full url) of a file or a folder?
On OS X "El Capitan", 

Option+Command+C the selected file/folder

OR


option right click the file/folder (in Finder)
Select 'Copy "file/folder" as Pathname'.





  Copy file path in Finder
  
  You now have the option to copy the path to a
  file without copying the file itself, perfect for working with files
  stored on a server. To copy the file path, right-click the file in the
  Finder, and then hold the Option key down and choose Copy as Pathname.
  
  (From Apple) http://www.apple.com/osx/all-features/#other-features