The php[architect] site has posted a tutorial showing you how to export Drupal nodes with Drush and a bit of regular PHP. Drush is a command line tool that makes working with Drupal outside of the interface simpler and easier to automate.

Drupal 8 development has shown that PHP itself, and the wider PHP community, already provides ways to solve common tasks. In this post, I’ll show you some core PHP functionality that you may not be aware of; pulling in packages and libraries via Composer is a topic for another day.

The tutorial walks through a more real-world situation of needing to export a CSV file that shows a list of nodes added to the site after a specific date. He points out some of the benefits of doing it the Drush way and starts in on the code/configuration you need to set the system up. He shows how to create the Drush command itself and update it with a method to export the newest nodes (after validating the date provided). He makes use of a SplFileObject to output the results from the EntityFieldQuery query out into to the CSV file. He makes use of PHP's generators functionality to only fetch the records a few at a time. Finally he includes the command to execute the export, defining the date to query the node set and how to push that output to a file.