How to send a mail when a plugin update found?

Question

Is there any hook for when any plugin update is found to trigger a mail using PHP? I found reference to upgrader_process_complete hook, but that is called after plugins are updated and not before.

Also, how can I fetch the list of plugins which have updates pending at a given time?

Answer 1

The relevant code is wp_update_plugins(). You can see that it stores its state in a site transient called 'update_plugins':

set_site_transient( 'update_plugins', $new_option );

and we can hook that:

• pre_set_site_transient_update_plugins - called at the start of set_site_transient()
• set_site_transient_update_plugins - called at the end, if the value was changed

Note that

• set_site_transient( 'update_plugins', ... ) is called twice as part of the update: once to update the last_checked timestamp, and once with the new-plugins-to-update list; the first call will always therefore have a changed value without necessarily having the list of updated plugins changed
• it can also be called when deleting plugins, to remove the update flag for any deleted plugin, but only once in this case.

I appreciate that hooking the site transient updates seems a bit of a hack, but there's no other obvious place to hook that the update check is complete. I have seen pay-for plugins hook these too as a way of generating update-needed for plugins hosted elsewhere.

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Alternatively of course you don't need to hook the actual update, but you can instead schedule a cron job that checks get_site_transient( 'update_plugins' ) (and update_themes and update_core) to generate the notification email.

Answer 2

With the answer of Rup, you can create a simple mail with the wp_mail function.

It would look like this:

 wp_mail( get_bloginfo( 'admin_email' ), 'Subject title here', 'Text for mail here'); 

With get_bloginfo( 'admin_email' ) you'll retrieve the admin's email you filled in during installation.