php实现使用正则将文本中的网址转换成链接标签

function text2links($str='') {
    if($str=='' or !preg_match('/(http|www\.|@)/i', $str)) { return $str; }
    $lines = explode("\n", $str); $new_text = '';
    while (list($k,$l) = each($lines)) {
        // replace links:
        $l = preg_replace("/([ \t]|^)www\./i", ".", $l);
        $l = preg_replace("/([ \t]|^)ftp\./i", ".", $l);
        $l = preg_replace("/(http:\/\/[^ )\r\n!]+)/i",
            "<a href=\">", $l);
        $l = preg_replace("/(https:\/\/[^ )\r\n!]+)/i",
            "<a href=\">", $l);
        $l = preg_replace("/(ftp:\/\/[^ )\r\n!]+)/i",
            "<a href=\">", $l);
        $l = preg_replace(
            "/([-a-z0-9_]+(\.[_a-z0-9-]+)*@([a-z0-9-]+(\.[a-z0-9-]+)+))/i",
            "<a href=\">", $l);
        $new_text .= $l."\n";
    }
    return $new_text;
}