Shortcode to output a download button after receiving a file upload field Merge Tag. It supports multiple files.

gv-download_links.php

<?php // DO NOT COPY THIS LINE
// How to use: inside a custom content field, use: [download_links urls="{File Upload:9}"]

function shortcode_download_links($atts) {
    // Capture the shortcode attributes
    $atts = shortcode_atts(
        array(
            'urls' => '',  // Default value for the merge tag
        ), 
        $atts
    );

    // Receive the value from the merge tag {upload file:9}
    $urls = $atts['urls'];

    // Check if the value is empty
    if (empty($urls)) {
        return ''; // Return empty if there are no URLs
    }

    // Split the URLs using the <br> tag as a delimiter
    $urls_array = preg_split('/<br\s*\/?>/i', $urls);

    // Initialize a string to store the buttons
    $output = '';

    // For each URL, create a download button
    foreach ($urls_array as $url) {
        // Remove whitespace from the URL
        $url = trim($url);

        // Check if the URL is not empty
        if (!empty($url)) {
            $output .= '<a class="download" href="' . esc_url($url) . '" download="">Download</a><br>';
        }
    }

    // Return the HTML with the buttons
    return $output;
}

// Register the shortcode [download_links urls="{upload file:9}"]
add_shortcode('download_links', 'shortcode_download_links');