regex help with getting tag content in PHP

问题

so I have the code

function getTagContent($string, $tagname) {

    $pattern = "/<$tagname.*?>(.*)<\/$tagname>/";
    preg_match($pattern, $string, $matches);


    print_r($matches);

}

and then I call

$url = "http://www.freakonomics.com/2008/09/24/wall-street-jokes-please/";
$html = file_get_contents($url);
getTagContent($html,"title");

but then it shows that there are no matches, while if you open the source of the url there clearly exist a title tag....

what did I do wrong?

回答1:

try DOM

$url  = "http://www.freakonomics.com/2008/09/24/wall-street-jokes-please/";
$doc  = new DOMDocument();
$dom  = $doc->loadHTMLFile($url);
$items = $doc->getElementsByTagName('title');
for ($i = 0; $i < $items->length; $i++)
{
  echo $items->item($i)->nodeValue . "\n";
}

回答2:

The 'title' tag is not on the same line as its closing tag, so your preg_match doesn't find it.

In Perl, you can add a /s switch to make it slurp the whole input as though on one line: I forget whether preg_match will let you do so or not.

But this is just one of the reasons why parsing XML and variants with regexp is a bad idea.

回答3:

Probably because the title is spread on multiple lines. You need to add the option s so that the dot will also match any line returns.

$pattern = "/<$tagname.*?>(.*)<\/$tagname>/s";

回答4:

Have your php function getTagContent like this:

function getTagContent($string, $tagname) {
    $pattern = '/<'.$tagname.'[^>]*>(.*?)<\/'.$tagname.'>/is';
    preg_match($pattern, $string, $matches);
    print_r($matches);
}

It is important to use non-greedy match all .*? for matching text between start and end of tag and equally important is to use flags s for DOTALL (matches new line as well) and i for ignore case comparison.

来源：https://stackoverflow.com/questions/6331265/regex-help-with-getting-tag-content-in-php

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