Export selected fields of all WordPress posts as CSV file

wp-exports-posts-csv.php

<?php
/*
 * Stick this in your functions.php, or include it from a separate file,
 * edit the post types you want to export,
 * then use the URL: http://your-blog.com/?_inventory=1
 *
 */
function return_csv_download($array_data, $filename){

  header('Content-Type: text/csv'); // you can change this based on the file type
  header('Content-Disposition: attachment; filename="' . $filename . '"');

  $out = fopen('php://output', 'w');
  foreach($array_data as $row){
    fputcsv($out, $row);
  }
  fclose($out);
}

function _emn_inventory_posts($posttypes){
  $args = array(
    'posts_per_page' => '-1',
    'post_status'    => 'publish',
    'orderby'        => 'date',
    'post_type'      => ''
  );

  $out = array();

  // @TODO - use data structure which combines titles and the functions to generate
  //       - the data for the column.
  $titles = array('Title', 'Date', 'Permalink', 'Post Type', 'Excerpt', 'Post ID');
  array_push($out, $titles);

  foreach($posttypes as $type) {

    $args['post_type'] = $type;

    $query = new WP_Query( $args);

    if ( $query->have_posts() ):
      while ( $query->have_posts() ): $query->the_post();
        $row = array(
          get_the_title(),
          get_the_date( 'M j, Y' ),
          get_permalink(),
          $type,
          get_the_excerpt(),
          get_the_ID()
        );
        array_push($out, $row);
      endwhile;
    endif;
    wp_reset_postdata();
  }
  return_csv_download($out, "posts.csv");
  //print_r( $out );

}

if( isset($_GET['_inventory']) ){
  // =============== EDIT THESE =============
  $posttypes = array('newsletter', 'press_release', 'comment_letter', 'in_the_news');
  //$posttypes = array('newsletter');
  _emn_inventory_posts($posttypes);
  die();
}


if( isset($_GET['_get_posttypes']) ){
  $args = array(
     'public'   => true,
     '_builtin' => false
  );
  $posttypes = get_post_types($args);
  print_r($posttypes);
  die();
}

Thank you :-)