_GET.html

<html>
<head>
  <title>PHP $_GET test</title>
</head>
<body>

  <?php

    $val_1=array_key_exists('val_1', $_GET) ? $_GET['val_1'] : '';
    $val_2=array_key_exists('val_2', $_GET) ? $_GET['val_2'] : '';

    echo "val_1: " . $val_1 . "<br>";
    echo "val_2: " . $val_2 . "<br>";

  ?>

  <p>

  <form action='#' method='get' style='background-color:#f93'>
     Val 1: <input type='text' name='val_1' value='<?php echo $val_1 ?>'><br>
     Val 2: <input type='text' name='val_2' value='<?php echo $val_2 ?>'><br>
    <input type='submit' value='go!'>
  </form>

</body>
</html>