Plugin writing: access file that was just uploaded

Question

I am having trouble finding a solution for following problem:

The user should upload a file in the menu of my plugin; the file is uploaded to the media folder by using media_handle_upload(file), where the file comes from the _FILES array - this works perfectly. The plugin then, however, should access that very same file (CSV) to extract data and present it on a page via a shortcode.

I can not, however, find out how to access that file in my plugin. I have looked into this: Access to Media Library, this: Accessing Media/Files outside the_content, and I have tried to find something in the wordpress codex. So far I could not find anything on this matter, however.

At the moment, my code for reading the file's contents looks like this:

$my_file = trailingslashit( wp_upload_dir() ) . 'MyFile.csv';
if (file_exists($my_file)) {
    return file_get_contents($my_file, FILE_USE_INCLUDE_PATH);
} else {
    return "No file found";
}

Thus my question is: how does my plugin access a file that is uploaded into the media folder but is not connected to any post or the like? Again, I intend to read the file's contents and process them further.

Answer 1

When you use media_handle_upload() to upload a file, it creates the attachment post in the database and return the ID of the attachment, or a WP_Error if the upload failed. This ID of the attachment is used to access uploaded file.
See documentation here. and an example here.

So path to your CSV file can be retrieved using get_attached_file() as follows:

$my_file = get_attached_file( $attachment_id ); // Full path

Documentation for get_attached_file() is here.
I hope this may help.