<form id="fileform" action="php/upload2.php" method="post" enctype="multipart/form-data">
                <div class="form-group"> <input name="upload[]" type="file" multiple="multiple" class="form-control-file text-white"> </div>
                <div class="form-group"><label><b class="text-white">Generated Identifier</b></label><input type="text" id="generatedidentifier" name="ab" class="form-control" disabled=""></div>
              </form>

if (isset($_POST["ab"]))
{
  $identifier = $_POST["ab"];
  echo $identifier;
  echo " is the ID";
}
else
{
  $identifier = null;
  echo "no ID supplied";
}