PHP - 如果href或src不以http，https或www开头，则删除特定的标签或img标签

I want to remove specific a and img tags from the $string_1 if <src> or <href> does not start with www, http or https inside <a> or <img> tags.

For example, $string_1 is converted to $string_2 by removing:

<img src="/wp-content/uploads/2014/06/photography-business-2.jpg" alt="photography business growth 1 650x430 6 Simple Ways To Help Grow Your Photography Business" width="650" height="430" class="alignnone size-large wp-image-609513" title="6 Simple Ways To Help Grow Your Photography Business"/>

and

<a href="/photography-business-growth/" rel="nofollow">Read more about Photography Business Growth &gt;</a>

because the src and href tags do not start with http, https or www.

$string_1 = '
<div class="mainpost"><p><img src="/wp-content/uploads/2014/06/photography-business-2.jpg" alt="photography business growth 1 650x430 6 Simple Ways To Help Grow Your Photography Business" width="650" height="430" class="alignnone size-large wp-image-609513" title="6 Simple Ways To Help Grow Your Photography Business"/></p>
<div class="mainpost"><p><img src="http://www.domain.com/wp-content/uploads/2014/06/photography-business-2.jpg" alt="photography business growth 1 650x430 6 Simple Ways To Help Grow Your Photography Business" width="650" height="430" class="alignnone size-large wp-image-609513" title="6 Simple Ways To Help Grow Your Photography Business"/></p>
<p><a href="http://domain.com/photography-business-growth/" rel="nofollow">Read more about Photography Business Growth &gt;</a></p>
<p>Photography Business Growth | With a world wide recession, photographers and small business owners are forced, more than ever, to think creatively, to think differently and outside of the box. With very little or no money to invest in your business, can you move forward? How can you build your brand and make sure to get happier, paying clients through your door?<br/><span id="more-609494"/></p>
<p>If you take good shots it doesn’t mean you’ll gain success and popularity among customers. For those of you who have survived start=up and built successful brands, you may be wondering which step to take next to grow your business beyond its current status. There are numerous possibilities, some of which we’ll outline here. You need to know how to sell yourself well! Everything is quite simple and you can do it yourself.</p>
<p><a href="/photography-business-growth/" rel="nofollow">Read more about Photography Business Growth &gt;</a></p>
';

$string_2= '
<div class="mainpost"><p></p>
<div class="mainpost"><p><img src="http://www.domain.com/wp-content/uploads/2014/06/photography-business-2.jpg" alt="photography business growth 1 650x430 6 Simple Ways To Help Grow Your Photography Business" width="650" height="430" class="alignnone size-large wp-image-609513" title="6 Simple Ways To Help Grow Your Photography Business"/></p>
<p><a href="http://domain.com/photography-business-growth/" rel="nofollow">Read more about Photography Business Growth &gt;</a></p>
<p>Photography Business Growth | With a world wide recession, photographers and small business owners are forced, more than ever, to think creatively, to think differently and outside of the box. With very little or no money to invest in your business, can you move forward? How can you build your brand and make sure to get happier, paying clients through your door?<br/><span id="more-609494"/></p>
<p>If you take good shots it doesn’t mean you’ll gain success and popularity among customers. For those of you who have survived start=up and built successful brands, you may be wondering which step to take next to grow your business beyond its current status. There are numerous possibilities, some of which we’ll outline here. You need to know how to sell yourself well! Everything is quite simple and you can do it yourself.</p>
';

Could you please help me to solve this problem? Thanks

Here is a first approach in PHP. It works for your example data. In $string_2 was the tailing "<p></p>" missing.

$string_3 = $string_1;
$pattern = "([^wh]|w[^w]|ww[^w]|h[^t]|ht[^t]|htt[^p])";
$string_3 = preg_replace("/<img src=\"".$pattern."[^>]*>/","",$string_3);
$string_3 = preg_replace("/<a href=\"".$pattern."[^>]*>[^<]*<\/a>/","",$string_3);

One solution would be doing this on the front-end with Javascript. If that's not an option, you can look into a PHP library to parse and traverse the DOM, such as http://simplehtmldom.sourceforge.net

I would use a DOM parser for this. Having a DOM document, you can use XPath to select the desired elements.

# Parse the HTML snippet into a DOM document
$doc = new DOMDocument();
$doc->loadHTML($string_1);

# Create an XPath selector
$selector = new DOMXPath($doc);

# Define the XPath query
# The syntax highlighter messed this up. Take it as it is!
$query = <<<EOF
  //a[not(starts-with(@href, "http"))
  and not(starts-with(@href, "www"))]
| //img[not(starts-with(@src, "http"))
  and not(starts-with(@src, "www"))]
EOF;

# Issue the XPath query and remove every resulting node
foreach($selector->query($query) as $node) {
    $node->parentNode->removeChild($node);
}

# Write back the modified `<div>` element into a string
echo $doc->saveHTML(
    $selector->query('//div[@class="mainpost"]')->item(0)
);