Button links to page in wordpress

Question

Currently I am working on a website where people could take courses from external websites. On the course page there is a button which would take you to that website. I made a meta_box which should hold an URL and use that URL for the button, it looks like this: link to form picture

But right now it does not take in this URL which I submit in this form. What part am I doing wrong? Here's my code:

This is in functions.php:

add_action('add_meta_boxes', 'mp_add_custom_metabox');
function mp_meta_callback( $post ) {
    echo "Add the link for the course button here:<br/>";
    echo "<form method='get'>";
    echo "<input type='text' name='buttonurl' placeholder='add a URL here'>";
    echo "<input type='submit' value='Add'>";
    echo "</form>";
}  

This is in the course single page:

<a href="<?php $_GET['buttonurl'];?>">
    <p>
        <div class="btn btn-primary take-course">
            Go to the course!
        </div>
    </p>
</a>

Thank you in advance for the help!

Answer 1

Try like this:

<?php
add_action( 'add_meta_boxes', 'cd_meta_box_add' );
function cd_meta_box_add()
{
    add_meta_box( 'my-meta-box-id', 'My First Meta Box', 'cd_meta_box_cb', 'post', 'normal', 'high' );
}

function cd_meta_box_cb()
{
    global $post;
    $values = get_post_custom( $post->ID );
    $button = isset( $values['buttonurl'] ) ? $values['buttonurl'] : '';?>
    <p>
        <label for="my_meta_box_text">Add the link for the course button here:</label>
        <input type='text' name='buttonurl' placeholder='add a URL here' value='<?php echo $button[0];?>'>
    </p>  <?php
}
add_action( 'save_post', 'cd_meta_box_save' );
function cd_meta_box_save( $post_id )
{
    // Make sure your data is set before trying to save it
    if( isset( $_POST['buttonurl'] ) )
        update_post_meta( $post_id, 'buttonurl', esc_url( $_POST['buttonurl']) );
}

You can then use the value in frontend like:

$button=get_post_meta( $post_id, 'buttonurl', true );


 <a href="<?php echo $button;?>">
    <p>
        <div class="btn btn-primary take-course">
            Go to the course!
        </div>
    </p>
</a>

Take a reference to : https://code.tutsplus.com/tutorials/how-to-create-custom-wordpress-writemeta-boxes--wp-20336