php regular expression to match string if NOT in an HTML tag

Question

I'm trying to solve this bug in Drupal's Hashtags module: http://drupal.org/node/1718154

I've got this function that matches every word in my text that is prefixed by "#", like #tag:

function hashtags_get_tags($text) {
    $tags_list = array();
    $pattern = "/#[0-9A-Za-z_]+/";
    preg_match_all($pattern, $text, $tags_list);
    $result = implode(',', $tags_list[0]);
    return $result;
    }

I need to ignore internal links in pages, such as <a href="#reference">link</a> , or, more in general, any word prefixed by # that appears inside an HTML tag (so preceeded by < and followed by >).

Any idea how can I achieve this?

Answer 1

Can you strip the tags first because matching (using the strip_tags function)?

function hashtags_get_tags($text) {

    $text = strip_tags($text);

    $tags_list = array();
    $pattern = "/#[0-9A-Za-z_]+/";
    preg_match_all($pattern, $text, $tags_list);
    $result = implode(',', $tags_list[0]);
    return $result;
}

A regular expression is going to be tricky if you want to only match hashtags that are not inside an HTML tag.

Answer 2

You could throw out the tags before hand using preg_replace

function hashtags_get_tags($text) {
$tags_list = array();
$pattern = "/#[0-9A-Za-z_]+/";
$text=preg_replace("/<[^>]*>/","",$text);
preg_match_all($pattern, $text, $tags_list);
$result = implode(',', $tags_list[0]);
return $result;
}

Answer 3

I made this function using PHP DOM .

It returns all links that have # in the href .

If you want it to only remove internal hash tags, replace this line:

if(strpos($link->getAttribute('href'), '#') === false) {

with this:

if(strpos($link->getAttribute('href'), '#') !== 0) {

This is the function:

function no_hashtags($text) {
    $doc = new DOMDocument();
    $doc->loadHTML($text);
    $links = $doc->getElementsByTagName('a');
    $nohashes = array();
    foreach($links as $link) {
        if(strpos($link->getAttribute('href'), '#') === false) {
            $temp = new DOMDocument();
            $elem = $temp->importNode($link->cloneNode(true), true);
            $temp->appendChild($elem);
            $nohashes[] = $temp->saveHTML();
        }
    }
    // return $nohashes;
    return implode('', $nohashes);
    // return implode(',', $nohashes);
}