function ReplaceBadWords($str, $bad_words, $replace_str){
    if (!is_array($bad_words)){ $bad_words = explode(',', $bad_words); }
    for ($x=0; $x < count($bad_words); $x++){
        $fix = isset($bad_words[$x]) ? $bad_words[$x] : '';
        $_replace_str = $replace_str;
        if (strlen($replace_str)==1){ 
            $_replace_str = str_pad($_replace_str, strlen($fix), $replace_str);
        }
        $str = preg_replace('/'.$fix.'/i', $_replace_str, $str);
    }
    return $str;
}
 
 
/*example-start*/
 
/*
** First example:
*/
 
// create some test "bla bla"
$str = <<<EOF
This is an test paragraph,
to test this badwords function.
Some bad words: fuck shit.
Sorry for that ;-)
EOF;
 
// this string will be used to replace the 
// bad words:
$replace_str = "@#$*!";
 
// create a array with words to replace:
$bad_words = array('shit','fuck');
 
// execute the function:
print ReplaceBadWords($str, $bad_words, $replace_str);
print "<hr/>\n";
 
 
/*
Another example:
 
 This tiny example shows to alternatives:
 
 1. You can use a string as source for bad words 
 2. If you give a "replace string" with the length of one letter
    it will automatically repeated to match the bad word length
*/
 
print ReplaceBadWords($str, 'fuck,shit,paragraph', '*');
 
/*example-end*/