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How to add rel="nofollow" to links with preg_replace()

Asked 2011-02-18T04:24:49.277
13

The function below is designed to apply rel="nofollow" attributes to all external links and no internal links unless the path matches a predefined root URL defined as $my_folder below.

So given the variables...

$my_folder = 'http://localhost/mytest/go/';
$blog_url = 'http://localhost/mytest';

And the content...

<a href="http://localhost/mytest/">internal</a>

<a href="http://localhost/mytest/go/hostgator">internal cloaked link</a>

<a href="http://cnn.com">external</a>

The end result, after replacement should be...

<a href="http://localhost/mytest/">internal</a>

<a href="http://localhost/mytest/go/hostgator" rel="nofollow">internal cloaked link</a>

<a href="http://cnn.com" rel="nofollow">external</a>

Notice that the first link is not altered, since its an internal link.

The link on the second line is also an internal link, but since it matches our $my_folder string, it gets the nofollow too.

The third link is the easiest, since it does not match the blog_url, its obviously an external link.

However, in the script below, ALL of my links are getting nofollow. How can I fix the script to do what I want?

function save_rseo_nofollow($content) {
$my_folder =  $rseo['nofollow_folder'];
$blog_url = get_bloginfo('url');
    preg_match_all('~<a.*>~isU',$content["post_content"],$matches);
    for ( $i = 0; $i <= sizeof($matches[0]); $i++){
        if ( !preg_match( '~nofollow~is',$matches[0][$i])
            && (preg_match('~' . $my_folder . '~', $matches[0][$i]) 
               || !preg_match( '~'.$blog_url.'~',$matches[0][$i]))){
            $result = trim($matches[0][$i],">");
            $result .= ' rel="nofollow">';
            $content["post_conten
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3 Answers

15

Here is the DOMDocument solution...

$str = '<a href="http://localhost/mytest/">internal</a>

<a href="http://localhost/mytest/go/hostgator">internal cloaked link</a>

<a href="http://cnn.com" rel="me">external</a>

<a href="http://google.com">external</a>

<a href="http://example.com" rel="nofollow">external</a>

<a href="http://stackoverflow.com" rel="junk in the rel">external</a>
';
$dom = new DOMDocument();

$dom->preserveWhitespace = FALSE;

$dom->loadHTML($str);

$a = $dom->getElementsByTagName('a');

$host = strtok($_SERVER['HTTP_HOST'], ':');

foreach($a as $anchor) {
        $href = $anchor->attributes->getNamedItem('href')->nodeValue;

        if (preg_match('/^https?:\/\/' . preg_quote($host, '/') . '/', $href)) {
           continue;
        }

        $noFollowRel = 'nofollow';
        $oldRelAtt = $anchor->attributes->getNamedItem('rel');

        if ($oldRelAtt == NULL) {
            $newRel = $noFollowRel;
        } else {
            $oldRel = $oldRelAtt->nodeValue;
            $oldRel = explode(' ', $oldRel);
            if (in_array($noFollowRel, $oldRel)) {
                continue;
            }
            $oldRel[] = $noFollowRel;
            $newRel = implode($oldRel,  ' ');
        }

        $newRelAtt = $dom->createAttribute('rel');
        $noFollowNode = $dom->createTextNode($newRel);
        $newRelAtt->appendChild($noFollowNode);
        $anchor->appendChild($newRelAtt);

}

var_dump($dom->saveHTML());

Output

string(509) "<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" "http://www.w3.org/TR/REC-html40/loose.dtd">
<html><body>
<a href="http://localhost/mytest/">internal</a>

<a href="http://localhost/mytest/go/hostgator">internal cloaked link</a>

<a href="http://cnn.com" rel="me nofollow">external</a>

&
answered 2011-02-18T05:09:15.670
11

Try to make it more readable first, and only afterwards make your if rules more complex:

function save_rseo_nofollow($content) {
    $content["post_content"] =
    preg_replace_callback('~<(a\s[^>]+)>~isU', "cb2", $content["post_content"]);
    return $content;
}

function cb2($match) { 
    list($original, $tag) = $match;   // regex match groups

    $my_folder =  "/hostgator";       // re-add quirky config here
    $blog_url = "http://localhost/";

    if (strpos($tag, "nofollow")) {
        return $original;
    }
    elseif (strpos($tag, $blog_url) && (!$my_folder || !strpos($tag, $my_folder))) {
        return $original;
    }
    else {
        return "<$tag rel='nofollow'>";
    }
}

Gives following output:

[post_content] =>
  <a href="http://localhost/mytest/">internal</a>
  <a href="http://localhost/mytest/go/hostgator" rel=nofollow>internal cloaked link</a>    
  <a href="http://cnn.com" rel=nofollow>external</a>

The problem in your original code might have been $rseo which wasn't declared anywhere.

answered 2011-02-18T04:52:03.347
0
<?

$str='<a href="http://localhost/mytest/">internal</a>
<a href="http://localhost/mytest/go/hostgator">internal cloaked link</a>
<a href="http://cnn.com">external</a>';

function test($x){
  if (preg_match('@localhost/mytest/(?!go/)@i',$x[0])>0) return $x[0];
  return 'rel="nofollow" '.$x[0];
}

echo preg_replace_callback('/href=[\'"][^\'"]+/i', 'test', $str);

?>
answered 2011-02-18T05:59:00.857

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