Executing batched operation with Drush

play.drush.inc

<?php

/**
 * @file
 * sites/all/drush/play.drush.php
 * 
 * Oftentimes one needs to run an operation on a list of things.
 * If this list is of variable length, running it in one process may
 * cause a time out and/or out of memory.
 *
 * This is a simple drush based way of dealing with this. There are
 * two drush commands, one which works out the list of things to
 * operate over and then uses drush_invoke_process() to execute a
 * second drush command on just one of the things.
 */

/**
 * Implements of hook_drush_command().
 */
function ebip_members_system_drush_command() {
  $items = array();

  $items['outer_command'] = array(
    'description' => 'The outer command works out the size of what needs to be done then runs the inner command multiple times.',
    'aliases' => array('oc'),
    'bootstrap' => DRUSH_BOOTSTRAP_DRUPAL_FULL,
  );

  $items['inner_command'] = array(
    'description' => 'The inner command works on a single item in the list of items to be processed. As this happens in its own process memory concerns are less.',
    'aliases' => array('ic'),
    'arguments' => [
      'id' => 'Id of thing to be worked on (e.g. node nid).',
    ],
    'bootstrap' => DRUSH_BOOTSTRAP_DRUPAL_FULL,
  );

  return $items;
}

/**
 * Outer command.
 */
function drush_play_outer_command() {
  // Get a list of things to process.
  $node_nids = $query = db_select('node', 'n');
    ->condition('n.type', 'article', '=')
    ->fields('d', ['nid'])
    ->execute()
    ->fetchCol(0);

  drush_print(dt('Found !count nodes of type article', ['!count' => count($node_ids)]));

  // Foreach node, run the inner command.
  foreach ($node_ids as $node_id) {
    drush_invoke_process('@self', 'inner_comand', [$node_id]);
  }
}

/**
 * Inner command
 */
function drush_play_inner_command($nid) {
  $node = node_load($nid);

  if (empty($node) || $node->type !== 'article') {
    return drush_set_error('play', 'Node id supplied is bad: ' . $nid);
  }

  // Do something useful and save the node... e.g.
  // $node->title = $node->title . ' - processed';
  // node_save($node);
}