How To Add Code To WP Without Plugin or Functions

Question

I know this is going to be a little strange because it's seemingly counter-intuitive. How do I add code to my WP multisite without adding a new plugin, and keeping it out of functions.php?

Purpose: I run a WP multisite instance that uses some custom code for sending emails using a self-signed certificate. I don't want anyone to know the code even exists. I don't want it to show in a menu, and I don't want it to be deleted during an update.

What I've Tried: I tried removing the header from the custom plugin I'm using now for this code, but that just deactivated the plugin.

I tried moving the file out of it's directory and placing it directly in the plugins folder, but that doesn't load it. I know because I lose email function.

I want to do the same for some custom shortcodes I have ready to go.

I know you might be asking why? It's easy to add the plugins and limit who can see them. I know this as well, but it would be even easier to add code without the need for creating a plugin. It also adds the benefit of completely hiding the code from customer/admin eyes. Sometimes admins can be a bigger problem than the customers.

For example, the email plugin I use has more lines of code in the header for the plugin, than the functional code itself.

Being able to add code snippets without the need for creating plugins would make my life much easier.

What I would like for a solution: A sub-directory within wp-content/ that will parse any code files included in this sub-directory.

Is WP presently capable of this?

Thank you.

Answer 1

In your case (I have done this on a number of sites of my own), I would use a "dummy" must-use plugin.

This plugin, which doesn't really need to say all that much, simply has a require statement to include the php code that I want to include from another location on the server.

MU plugins are active on all sites on the network, and the "edit plugin" interface does not interact with them. MU plugins don't even need headers, and with no headers present, all that is shown is the filename -- which again, you can make to say anything you want.

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Another option is to add a custom require line within the wp-config file. This is very early on in the WP process, so you may be limited with what your custom code can do.

Answer 2

I can only think of these options:

1. You could make PHP code not related to WP but that have access to the database and add some triggers, that will depend on what your custom code does and it will be complex too (WP db knowledge), Example: look at the posts table for new entries and send an email about it; it will be like creating a small php program.
2. another posibility its to do a normal plugin and restrict it to a specific user (superadmin or by ID), file permissions too so only a specific user can open the file, the thing with that is they will know something is there, a dummy interface can be used too for this.

and yeah like you said is counter-intuitive, use WP but without using it, that will be the database way, you will use the data WP creates but you will not use WP code.