Creating multi purpose button in html

Simplest Way:

    <form method="post" action="" enctype="multipart/form-data" name="form1">
        <input   name="file" type="file" onchange="if($(this).val().length){$(this).hide().next().show()}" class="box"/>         
        <input type="submit" id="mybut" value="Upload" style="display:none;" name="Submit"/>
    </form>     

Without Jquery, Only JavaScript

    <form method="post" action="" enctype="multipart/form-data" name="form1">
        <input   name="file" type="file" onchange="this.nextElementSibling.style.display = 'block'; this.style.display = 'none';" class="box"/>         
        <input type="submit" id="mybut" value="Upload" style="display:none;" name="Submit"/>
    </form>