PHP回发输入的值

I have the following code:

<form>
   .............
    <?php
    if (!isset($_FILES['before']['name'] || !isset($_FILES['after']['name']) 
        echo '<input type="submit" value="Show Image">'
    else 
        echo '<input type="submit" value="Upload">'
    ?>
</form>

in my postback how do I check whether it's one or the other?

You give both submit buttons the same name and then check its value in the postback with...

$_POST['submit_name']