正则表达式匹配，并且<a href>?

Question

I found this code posted on SO to change text links into hyperlinks:

function auto_link_text($text) 
{ 
    $pattern = '#\b(([\w-]+://?|www[.])[^\s()<>]+(?:\([\w\d]+\)|([^[:punct:]\s]|/)))#'; 
    $callback = create_function('$matches', ' 
    $url  = array_shift($matches); 
    $url_parts = parse_url($url); 

    $text = parse_url($url, PHP_URL_HOST) . parse_url($url, PHP_URL_PATH); 
    $text = preg_replace("/^www./", "", $text); 

    $last = -(strlen(strrchr($text, "/"))) + 1; 
    if ($last < 0) { 
     $text = substr($text, 0, $last) . "&hellip;"; 
    } 

    return sprintf(\'<a rel="nowfollow" href="%s">%s</a>\', $url, $text); 
    '); 

    return preg_replace_callback($pattern, $callback, $text); 
} 

However, it seems to change them into hyperlinks even if they are already a part of a hyperlink so you end up with something like <a href="<a href (etc). I figure what I could do is check for an already formatted hyperlink and if I don't find one, I can do that function. Or even put the check in the function. So something like:

function auto_link_text($text) 
{ 
    if preg_match(proper stuff in here){ 
     return $text; 
     }else{ 
     $pattern = '#\b(([\w-]+://?|www[.])[^\s()<>]+(?:\([\w\d]+\)|([^[:punct:]\s]|/)))#'; 
     $callback = create_function('$matches', ' 
    $url  = array_shift($matches); 
    $url_parts = parse_url($url); 

    $text = parse_url($url, PHP_URL_HOST) . parse_url($url, PHP_URL_PATH); 
    $text = preg_replace("/^www./", "", $text); 

    $last = -(strlen(strrchr($text, "/"))) + 1; 
    if ($last < 0) { 
     $text = substr($text, 0, $last) . "&hellip;"; 
    } 

    return sprintf(\'<a rel="nowfollow" href="%s">%s</a>\', $url, $text); 
    '); 

    return preg_replace_callback($pattern, $callback, $text); 
} 
} 

Or perhapse the regex in the function should be changed.

Answer 1

Add (?<!href=") just after the first # of your regex. This will ensure that it's not already inside a tag.