'www.google.com',
'facebook' => 'www.facebook.com',
);
$text = "
Search on google for facebook
Search on google for facebook
";
$sentence = preg_replace_callback('~(]*>)(.*?)()~s', function($m) use ($change) {
return $m[1] . preg_replace(
array_map(function ($x) { return '@(?<=\W|^)('.preg_quote($x, "@").')(?=\W|$)@i'; }, array_keys($change)),
array_map(function ($y) { return '$1'; }, array_values($change)),
$m[2]). $m[3]; }
, $text);
echo $sentence;