$num = 'www.49028c.com';
$string = "this string has four words. <br>";
$string = ereg_replace ('four', $num, $string);
echo $string;

$num = '49';
$string = "this string has four words";
$string = ereg_replace ('four', $num, $string);
echo $string;

$string ="測試用文字";
echo "**********$string**********<p>";
$string = ereg_replace ("^", "<br>", $string);
$string = ereg_replace ("$", "<br>", $string);
echo "==========$string==========";