Wordcensoring in php

From the following example, you can learn the usage of form, textarea, isset, strtolower and str_replace. Every word 'love' you type in the text box, the codes will change with the word 'hate'.

<?php
$find = 'love';
$replace = 'hate';
if(isset($_POST['user_input']) && !empty($_POST['user_input'])){
   $user_input = strtolower($_POST['user_input']);
   $user_input_new = str_replace($find, $replace, $user_input);
   echo $user_input_new.'</br>';
}else{
  echo 'Please fill in the text box!';
}
?>

<form action = "wordcensoring.php" method = "POST">
<textarea name = "user_input" cols = "40" widths = "500"></textarea></br></br>
<input type = "submit" value = "Submit">
</form>