How to ping search engines with curl

when you add new story or update an existing one it may take a few weeks for search engine bots to re-index your site, I've noticed however that some sites get re-index very shortly after adding or updating content on their website, which got me thinking how did they do it? the answer they ping search engines when ever there's any changes which informs the search engine bots there's been a change and to read the site's sitemap again this process is usually done within a few minutes of sending the ping.