Regex to change

问题:

I need to look inside a string of HTML and change all <img> tags where the src attribute is a relative address, to an absolute URL. So this:

<img src="puppies.jpg">

needs to become:

<img src="http://sitename.com/path/puppies.jpg">

while ignoring <img> tags whose src attribute is already absolute.

I'm using PHP and assume that I'll need to run this through preg_replace(). Help! And Thanks!

回答1:

This is not a job for a regular expression. It's a job for an XML/DOM parser.

I'd give DOMDocument a shot.

$DOM = new DOMDocument;
$DOM->loadHTML($html);

$imgs = $DOM->getElementsByTagName('img');
foreach($imgs as $img){
    $src = $img->getAttribute('src');
    if(strpos($src, 'http://sitename.com/path/') !== 0){
        $img->setAttribute('src', "http://sitename.com/path/$src");
    }
}

$html = $DOM->saveHTML();

回答2:

This is not a job for a regular expression. It's a job for an XML/DOM parser.

Nope it's not. If you just want to add a prefix to each src attribute, it's best to use simple string functions and don't even think about xml, regex or dom parsing…

$str = str_replace('<img src="', '<img src="http://prefix', $str);

You can clean up wrong links (already absolute ones) afterwards

$str = str_replace('<img src="http://prefixhttp://', '<img src="http://', $str);

Do not blow up your code with regexp/dom if you can avoid it.