Question

I’m trying to extract the first src attribute of an image in a block of HTML text like this:

Lorem ipsum <img src="http://example.com/img.jpg" />consequat.

I have no problem creating the regular expression to match the src attribute, but how do I return the first matched src attribute, instead of replacing it?

From pouring over the PHP manual, it seems like preg_filter() would do the trick, but I can’t rely on end users having a PHP version greater than 5.3.

All the other PHP regular expression functions seem to be variations of preg_match(), returning a Boolean value, or preg_replace, which replaces the match with something. Is there a straightforward way to return a regular expression match in PHP?

Answer 1

You can use the third parameter of preg_match to know what was matched (it’s an array, passed by reference):

int preg_match  ( string $pattern  , 
    string $subject  [, array &$matches  [, 
    int $flags  [, int $offset  ]]] )

If matches is provided, then it is
filled with the results of search.
$matches[0] will contain the text that
matched the full pattern, $matches[1]
will have the text that matched the
first captured parenthesized
subpattern, and so on.

For instance, with this portion of code:

$str = 'Lorem ipsum dolor sit amet, adipisicing <img src="http://example.com/img.jpg" />consequat.';

$matches = array();
if (preg_match('#<img src="(.*?)" />#', $str, $matches)) {
    var_dump($matches);
}

You’ll get this output:

array
  0 => string '<img src="http://example.com/img.jpg" />' (length=37)
  1 => string 'http://example.com/img.jpg' (length=23)

(Note that my regex is overly simplistic — and that regex are generally not "the right tool" when it comes to extracting data from some HTML string…)