php正则替换中变量的指定字符

$str = preg_quote('(银子)');
$txt = '我的呢称(银子)';
echo preg_replace("/($str)/","$1",$txt);
?>

$str = quotemeta('(银子)');
$txt = '我的呢称(银子)';
echo preg_replace("/($str)/","$1",$txt);
?>

$text  = “foobar123fooabcbar”;

$text = preg_replace(“/foo(?=bar)/”, “***”, $text);

$text  = “foobar123fooabcbar”;

$text = preg_replace(“/(?

$text  = “foobar123fooabcbar”;

$text = preg_replace(“/foo(?!bar)/”, “***”, $text);

$text  = “foobar123fooabcbar”;

$text = preg_replace(“/(?