$num = 'www.jb51.net';
$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;

$string ="测试用文字";
echo "**********$string**********p>";
$string = ereg_replace ("^", "br>", $string);
$string = ereg_replace ("$", "br>", $string);
echo "==========$string==========";