PHP - Extracting two values from a line

Question

I'm a beginner with regular expressions and am working on a server where I cannot instal anything (does using DOM methods require the instal of anything?).

I have a problem that I cannot solve with my current knowledge. I would like to extract from the line below the album id and image url. There are more lines and other url elements in the string (file), but the album ids and image urls I need are all in strings similar to the one below:

<a href="http://www.mydomain.com/galeria/thumbnails.php?album=774" target="_blank"><img alt="/" src="http://img255.imageshack.us/img00/000/000001.png" height="133" width="113"></a>

So in this case I would like to get '774' and 'http://img255.imageshack.us/img00/000/000001.png'

I've seen multiple examples of extracting just the url or one other element from a string, but I really need to keep these both together and store these in one record of the database.

Any help is really appreciated!

FYI, You can see what you have installed on your server by creating a script with a body like: <?php echo phpinfo(); ?> SimpleXML is a good way to go for this, but it requires the libxml PHP extension. us2.php.net/manual/en/simplexml.requirements.php — Joshua Kaiser
– Joshua Kaiser, Commented Nov 19, 2012 at 21:55

nickb · Accepted Answer · 2012-11-19 22:12:42Z

4

Since you are new to this, I'll explain that you can use PHP's HTML parser known as DOMDocument to extract what you need. You should not use a regular expression as they are inherently error prone when it comes to parsing HTML, and can easily result in many false positives.

To start, lets say you have your HTML:

$html = '<a href="http://www.mydomain.com/galeria/thumbnails.php?album=774" target="_blank"><img alt="/" src="http://img255.imageshack.us/img00/000/000001.png" height="133" width="113"></a>';

And now, we load that into DOMDocument:

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

Now, we have that HTML loaded, it's time to find the elements that we need. Let's assume that you can encounter other <a> tags within your document, so we want to find those <a> tags that have a direct <img> tag as a child. Then, check to make sure we have the correct nodes, we need to make sure we extract the correct information. So, let's have at it:

$results = array();

// Loop over all of the <a> tags in the document
foreach( $doc->getElementsByTagName( 'a') as $a) {
    // If there are no children, continue on
    if( !$a->hasChildNodes()) continue;

    // Find the child <img> tag, if it exists
    foreach( $a->childNodes as $child) {
         if( $child->nodeType == XML_ELEMENT_NODE && $child->tagName == 'img') { 
             // Now we have the <a> tag in $a and the <img> tag in $child
             // Get the information we need:
             parse_str( parse_url( $a->getAttribute('href'), PHP_URL_QUERY), $a_params);
             $results[] = array( $a_params['album'], $child->getAttribute('src'));              
         }
    }
}

A print_r( $results); now leaves us with:

Array
(
    [0] => Array
        (
            [0] => 774
            [1] => http://img255.imageshack.us/img00/000/000001.png
        )

)

Note that this omits basic error checking. One thing you can add is in the inner foreach loop, you can check to make sure you successfully parsed an album parameter from the <a>'s href attribute, like so:

if( isset( $a_params['album'])) {
    $results[] = array( $a_params['album'], $child->getAttribute('src'));        
}

Every function I've used in this can be found in the PHP documentation.

answered Nov 19, 2012 at 22:12

nickb

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2 Comments

Joshua Kaiser Over a year ago

Very thorough explanation. If I could, I'd give it an extra +1 for spelling it out so well. Just one thing - wouldn't it be more efficient to use an xpath query to get the image under the anchor tag than to iterate through each of the child nodes?

nickb Over a year ago

@Joshua - It would, but I didn't want to introduce XPath - I felt it was too much for the scope of this solution.

Joshua Kaiser · Accepted Answer · 2012-11-20 21:54:23Z

2

If you've already narrowed it down to this line, then you can use a regex like the following:

$matches = array();
preg_match('@.+album=(\d+).+src="([^"]+)@', $yourHtmlLineHere, $matches);

Now if you

echo $matches[1];
echo " ";
echo $matches[2];

You'll get the following:

774 http://img255.imageshack.us/img00/000/000001.png

edited Nov 20, 2012 at 21:54

answered Nov 19, 2012 at 22:02

Joshua Kaiser

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6 Comments

nickb Over a year ago

Regexes are incredibly brittle when parsing HTML, and this will fail for many input test cases. If this exists in the document: <p>album=5 src="something"</p>, this would pick that up as a match.

Joshua Kaiser Over a year ago

@nickb I agree completely. If it's an option I think DomDocuments are definitely the way to go. The asker was clearly unsure if he had that option available to him, and asked specifically about regex, hence my answer and advice to check his phpinfo() output, above ;)

Marijn Schoo Over a year ago

This indeed works, but it seemed very unpredictable. Sometimes it didn't work because of certain quotes used in a previous line, etc... The DOMDocument HTML parser works fluently :) Thank you very much for this code and the additional information.

Joshua Kaiser Over a year ago

@MarijnSchoo glad you got it going :)

Joshua Kaiser Over a year ago

@MarijnSchoo Thanks. That's my bad. It's because I used preg_match_all instead of preg_match. I'll update my answer just for clarity.

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