Drupal 8: Empty all field values of a specific field

delete-field-values.php

<?php

/**
 * @file
 * This file deletes all field values of a specific field.
 *
 * It is meant to be run with 'drush php-script'.
 *
 * It is useful if you want to delete all data from a field,
 * for example to change field storage settings of a configurable
 * field, without deleting the actual entities.
 */

// Change these according to your use-case.
$entity_type_id = 'node';
$field_name = 'body';

/** @var \Drupal\Core\Entity\ContentEntityStorageInterface $storage */
$storage = \Drupal::entityTypeManager()->getStorage($entity_type_id);

/** @var \Drupal\Core\Entity\ContentEntityInterface $entity */
foreach ($storage->loadMultiple() as $entity) {
  $changed = FALSE;
  /** @var \Drupal\Core\Language\LanguageInterface $language */
  foreach ($entity->getTranslationLanguages(TRUE) as $language) {
    $translation = $entity->getTranslation($language->getId());
    $items = $translation->get($field_name);
    if (!$items->isEmpty()) {
      $items->setValue([]);
      $changed = TRUE;
    }
  }
  if ($changed) {
    $entity->save();
  }
}

$revision_ids = array_keys($storage->getQuery()->allRevisions()->execute());
foreach ($revision_ids as $revision_id) {
  /** @var \Drupal\Core\Entity\ContentEntityInterface $revision */
  $revision = $storage->loadRevision($revision_id);
  if (!$revision->get($field_name)->isEmpty()) {
    $storage->deleteRevision($revision_id);
  }

  $changed = FALSE;
  /** @var \Drupal\Core\Language\LanguageInterface $language */
  foreach ($revision->getTranslationLanguages(TRUE) as $language) {
    $translation = $revision->getTranslation($language->getId());
    $items = $translation->get($field_name);
    if (!$translation->get($field_name)->isEmpty()) {
      $storage->deleteRevision($revision_id);
      continue 2;
    }
  }
}