descarga.php

<?php
/*
Plugin Name: Descargas MetaBox
Plugin URI: http://basdower.com
Description: Descargas MetaBox agregara un campo de texto para su descarga.
Version: 1.0
Author: Basdower
Author URI: http://basdower.com
License: GPL2
*/

function link_get_meta( $value ) {
    global $post;

    $field = get_post_meta( $post->ID, $value, true );
    if ( ! empty( $field ) ) {
        return is_array( $field ) ? stripslashes_deep( $field ) : stripslashes( wp_kses_decode_entities( $field ) );
    } else {
        return false;
    }
}
function link_add_meta_box() {
    add_meta_box(
        'link-link',
        __( 'Descarga', 'link' ),
        'link_html',
        'post',
        'normal',
        'default'
    );
}
add_action( 'add_meta_boxes', 'link_add_meta_box' );
function link_html( $post) {
    wp_nonce_field( '_link_nonce', 'link_nonce' ); ?>
    <table class="form-table">
        <tr>
            <th style="width:10%"><label for="link_by_basdower">Link</label></th>
            <td><input type="text" name="link_by_basdower" id="link_by_basdower" value="<?php echo link_get_meta( 'link_by_basdower' ); ?>" size="30" style="width:97%"> Ingresa el enlace de tu descarga</td>
        </tr>
    </table>
<?php
}
function link_save( $post_id ) {
    if ( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE ) return;
    if ( ! isset( $_POST['link_nonce'] ) || ! wp_verify_nonce( $_POST['link_nonce'], '_link_nonce' ) ) return;
    if ( ! current_user_can( 'edit_post', $post_id ) ) return;

    if ( isset( $_POST['link_by_basdower'] ) )
        update_post_meta( $post_id, 'link_by_basdower', esc_attr( $_POST['link_by_basdower'] ) );
}
add_action( 'save_post', 'link_save' );
?>