Drupal 8 installation (bash) script. I want the latest stable v8 version each time. But how?
As mradcliffe said in the comment, if you don't want to use composer (which I would really recommend you look into), you can simply use drush. You just need this:

drush dl drupal


This defaults to the latest stable Drupal 8 version. If you want to have a git clone (which is way slower), you can tell drush to do that too:

drush dl --package-handler=git_drupalorg drupal