A simple WordPress plugin that allows you to upload files programatically. Visit https://www.davidangulo.xyz/ for more information.

upload.php

<?php
/*
Plugin Name: Upload Files Programatically
Plugin URI: https://wordpress.org/plugins/
Description: Just another file uploader plugin.
Version: 1.0.0
Author: David Angulo
Author URI: https://www.davidangulo.xyz/
*/

function myFileUploader() {
	if(isset($_POST["submit"])) {
		wp_upload_bits($_FILES['fileToUpload']['name'], null, file_get_contents($_FILES['fileToUpload']['tmp_name']));
	}
	echo '<form action="" method="post" enctype="multipart/form-data">
    	<input type="file" name="fileToUpload" id="fileToUpload">
    	<input type="submit" value="Upload Image" name="submit">
	</form>';
}

function myFileUploaderRenderer() {
	ob_start();
	myFileUploader();
	return ob_get_clean();
}

add_shortcode("custom_file_uploader","myFileUploaderRenderer");

//Visit the tutorial for more information
//https://www.davidangulo.xyz/website-development/how-to-upload-files-in-wordpress-programmatically/