Delete all nodes of a particular bundle (content type). [Without Views Bulk Operations]

gistfile1.php

<?php

// Instantiate a new Entity Field Query
$efq = new EntityFieldQuery();

// Add a condition of entity_type = node and bundle = article.
$results = $efq->entityCondition('entity_type', 'node')
->entityCondition('bundle', 'article')
->execute();


if (!empty($results['node'])) {
  // Loop through each of the results and execute node_delete().
  foreach($results['node'] as $node) {
    node_delete($node->nid);
  }
}