How to display php form result in the html if php processing is not in the same page without using ajax?

You can simply place the code in the process.php file inside the forms span tag.

<form action="form.php" method="POST">
<input type="text" name="message">
<input type="submit" value="Submit">
</form>
<span class="result">
<?php 
    if(isset($_POST['message']))
    {
        $message = $_POST['message'];
        if(!empty($message))
        {
            echo 'Your message: '.$message;
        }
        else
        {
            echo 'Please enter some message.';
        }
    }
?>
</span>

Try this. It will post the form values in same page

<form action="form.php" method="POST">
<input type="text" name="message">
<input type="submit" value="Submit">
</form>
<span class="result"></span>

<?php 
if(isset($_POST['message'])){
  $message = $_POST['message'];
  if(!empty($message)){
    echo 'Your message: '.$message;
  }else{
    echo 'Please enter some message.';
  }
}

OK this is one way of doing it: In form.php,

<form action="process.php" method="POST">
    <input type="text" name="message">
    <input type="submit" value="Submit">
</form>

<?php
    $var = $_GET['text'];
    echo "<span class=\"result\"> $var </span>";
?>

Then in process.php do this:

<?php 
   if(isset($_POST['message'])){
    $message = $_POST['message'];
      if(!empty($message)){
         // echo 'Your message: '.$message;
         header("location: form.php?text=$message")
      }else{
        echo 'Please enter some message.';
      }
}
?>

There are a few drawbacks using this method:

1. Variable $message is passed through the URL and so should not be too long as URLs have length limits
2. Using $_GET[] makes message visible on the URL so passwords and other sensitive information should no be used as the message.

I hope this helps.