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", "\1http://www.", $l);
        $l = preg_replace("/([ t]|^)ftp./i", "\1ftp://ftp.", $l);
        $l = preg_replace("/(http://[^ )rn!]+)/i",
            "<a href="\1">\1</a>", $l);
        $l = preg_replace("/(https://[^ )rn!]+)/i",
            "<a href="\1">\1</a>", $l);
        $l = preg_replace("/(ftp://[^ )rn!]+)/i",
            "<a href="\1">\1</a>", $l);
        $l = preg_replace(
            "/([-a-z0-9_]+(.[_a-z0-9-]+)*@([a-z0-9-]+(.[a-z0-9-]+)+))/i",
            "<a href="mailto:\1">\1</a>", $l);
        $new_text .= $l."n";
    }
    return $new_text;
}