如果你只需要为最近50篇文章保留图像，我认为cron作业或WP cron不是你能做的最好的事情，在WordPress中，你可以知道一篇文章何时发布，你可以每次都运行一个例程，删除50篇之前发布的文章的图像。

这很简单，性能更好（如果无事可做，则什么也不做，无论是否有要删除的内容，cron作业都会运行）。

工作流程非常简单：

每次发布帖子时，获取第51个帖子id（按发布日期排序）

代码：

add_action( \'save_post\', \'cleanup_old_post_images\', 10, 3 );

function cleanup_old_post_images( $post_ID, $post, $update ) {
  if ( $update ) return; // do nothing on update
  $postid51th = get51th_postid(); // see below
  if ( ! empty( $postid51th ) && is_numeric( $postid51th ) ) {
    delete_post_media( $postid51th ); // see below, function in OP
  }
}

function get51th_postid() {
  return $GLOBALS[\'wpdb\']->get_var(
    "SELECT ID FROM " . $GLOBALS[\'wpdb\']->posts .
    " WHERE post_type = \'post\' AND post_status = \'publish\' ORDER BY post_date DESC
    LIMIT 50, 1"
  ); 
}

function delete_post_media( $post_id ) {
  $attachments = get_posts( array(
    \'post_type\'      => \'attachment\',
    \'nopaging\'       => TRUE,
    \'post_parent\'    => $post_id
  ) );
  if ( empty( $attachments ) ) return; // added this line to prevent errors
  foreach ( $attachments as $attachment ) {
    if ( false === wp_delete_attachment( $attachment->ID ) ) {
      // Log failure to delete attachment.
    }
  }
}

这适用于将代码放入站点后发布的帖子，但您可以编写run once函数来删除旧帖子的图像

add_action( \'shutdown\', \'delete_older_attachments\' );

function delete_older_attachments() {

  // run only on admin and use a transient to run once
  if ( ! is_admin() || get_transient(\'get_older_postids\') ) return;     

  // the query to exclude last 50 posts
  $latest_query = "SELECT ID FROM " . $GLOBALS[\'wpdb\']->posts .
    " WHERE post_type = \'post\' AND post_status = \'publish\' ORDER BY post_date DESC
    LIMIT 50"
  );

  // get older posts ids
  $older_ids = $GLOBALS[\'wpdb\']->get_row(
    "SELECT ID FROM " . $GLOBALS[\'wpdb\']->posts . 
    " WHERE post_type = \'post\' AND post_status = \'publish\'
    AND ID NOT IN (" . $latest_query . ")"
  );

  // get attachments for older posts
  if ( ! empty( $older_ids ) && is_array( $older_ids )  ) {
    $attachments = $GLOBALS[\'wpdb\']->get_row(
      "SELECT ID FROM " . $GLOBALS[\'wpdb\']->posts . 
      " WHERE post_type = \'attachments\'
      AND post_parent IN (" . implode( \',\', $older_ids ) . ")"
    );
  }

  if ( isset($attachments) && ! empty( $attachments ) && is_array( $attachments )  ) {
    foreach ( $attachments as $attachment ) {
      if ( false === wp_delete_attachment( $attachment ) ) {
        // Log failure to delete attachment.
      }
    }
    // set the transient to assure run once
    set_transient( \'get_older_postids\', 1 );
  }
}