<?php
/**
 * Obfuscates a word by replacing all but the first and the last letters with *
 * @param string $word The unscrabled word.
 * @return string
 */
function obfuscateWord($word)
{
    $first = $word[0];
    $last = $word[strlen($word)-1];
    $middle = "";
    for($i = 0; $i < strlen($word)-2; $i++)
    {
        $middle .= "*";
    }
    return $first . $middle . $last;
}
 
// A list of banned words
$wordList = array('duck', 'fick');
 
// Compile the regular expression that searches for the words in the list.
$regexp = '/(' . implode('|', $wordList) . ')/ie';
 
// The "callback" for the regular exrepssion matches.
// This calls the obfuscateWord function, passing the matches word and replacing it
// with the scrambled word.
$replace = 'obfuscateWord("$1");';
 
// Example text to use
$text = "There is a duck on the fick!";
 
// Do the actual replace.
$text = preg_replace($regexp, $replace, $text);
 
echo $text;
?>