$bad = array("bad", "words", "here");
$good = array("good", "words", "here");

function noswear($string)
{
    if ($string)
    {
        $bad = array("bad", "words");
        $good = array("good", "words");
        $newstring = str_replace($bad, $good, $string);
        return $newstring;
}

echo noswear("I see bad words coming!");

function badWordsFilter($inputWord) {
  $badWords = Array("bad","words","here");
  for($i=0;$i<count($badWords);$i++) {
     if($badWords[$i] == strtolower($inputWord))
        return true;
     }
  return false;
}

if (badWordsFilter("bad")) {
    echo "Bad word was found";
} else {
    echo "No bad words detected";
}

function badWordsFilter($inputWord) {
  $badWords = Array("bad","words","here");
     if(in_array(strtolower($inputWord), $badWords) ) {
        return true;
     }
  return false;
}

$wordsTransform = array(
  'shit' => 'ship'
);

$string = "Rolling In The Deep by Adeln
n
There's a fire starting in my heartn
Reaching a fever pitch, and it's bringing me out the darkn
Finally I can see you crystal clearn
Go ahead and sell me out and I'll lay your shit bare";

$string = strtr($string, $wordsTransform);

//
// Written by Patrick Rauchfuss
class String
{
    public static function stritr(&$string, $from, $to = NULL)
    {
        if(is_string($from))
            $string = preg_replace("/b{$from}b/i", $to, $string);

        else if(is_array($from))
        {
            foreach ($from as $key => $val)
                self::stritr($string, $key, $val);
        }
        return preg_quote($string); // return and add a backslash to special characters
    }
}

$wordsTransform = array(
            'shit' => 'ship'
        );

String::stritr($string, $wordsTransform);

$input_string = 'This Could be interesting but should it be? Perhaps this 'would' work; or couldn't it?';

$bad_words  = array('could', 'would', 'should');
$good_words = array('might', 'will');

function replace_words($matches){
    global $good_words;
    return $matches[1].$good_words[rand(0, count($good_words)-1)].$matches[3];
}

echo preg_replace_callback('/(^|b|s)('.implode('|', $bad_words).')(b|s|$)/i', 'replace_words', $input_string);

/(START OR WORD_BOUNDARY OR WHITE_SPACE)(BAD_WORD)(WORD_BOUNDARY OR WHITE_SPACE OR END)/i

global $good_words; <-- Makes the $good_words variable accessible from within the function
$matches[1] <-- The word boundary before the matched word
$matches[3] <-- The word boundary after  the matched word
$good_words[rand(0, count($good_words)-1] <-- Selects a random good word from $good_words

echo preg_replace_callback(
        '/(^|b|s)('.implode('|', $bad_words).')(b|s|$)/i',
        function ($matches) use ($good_words){
            return $matches[1].$good_words[rand(0, count($good_words)-1)].$matches[3];
        },
        $input_string
    );

function clean_string($input_string, $bad_words, $good_words){
    return preg_replace_callback(
        '/(^|b|s)('.implode('|', $bad_words).')(b|s|$)/i',
        function ($matches) use ($good_words){
            return $matches[1].$good_words[rand(0, count($good_words)-1)].$matches[3];
        },
        $input_string
    );
}

echo clean_string($input_string, $bad_words, $good_words);

This will be interesting but might it be? Perhaps this 'will' work; or couldn't it?
This might be interesting but might it be? Perhaps this 'might' work; or couldn't it?
This might be interesting but will it be? Perhaps this 'will' work; or couldn't it?

foreach($bad_words as $key=>$word){
    $bad_words[$key] = preg_quote($word);
}

b$h1tb <---Will not match