Extracting the body text of an HTML document using PHP

问题

I know it's better to use DOM for this purpose but let's try to extract the text in this way:

<?php


$html=<<<EOD
<html>
<head>
</head>
<body>
<p>Some text</p>
</body>
</html>
EOD;


        preg_match('/<body.*?>/', $html, $matches, PREG_OFFSET_CAPTURE);

        if (empty($matches))
            exit;

        $matched_body_start_tag = $matches[0][0];
        $index_of_body_start_tag = $matches[0][1];

        $index_of_body_end_tag = strpos($html, '</body>');


        $body = substr(
                        $html,
                        $index_of_body_start_tag + strlen($matched_body_start_tag),
                        $index_of_body_end_tag - $index_of_body_start_tag + strlen($matched_body_start_tag)
        );

echo $body;

The result can be seen here: http://ideone.com/vH2FZ

As you can see, I am getting more text than expected.

There is something I don't understand, to get the correct length for the substr($string, $start, $length) function, I am using:

$index_of_body_end_tag - $index_of_body_start_tag + strlen($matched_body_start_tag)

I don't see anything wrong with this formula.

Could somebody kindly suggest where the problem is?

Many thanks to you all.

EDIT:

Thank you very very much to all of you. There is just a bug in my brain. After reading your answers, I now understand what the problem is, it should either be:

  $index_of_body_end_tag - ($index_of_body_start_tag + strlen($matched_body_start_tag));

Or:

  $index_of_body_end_tag - $index_of_body_start_tag - strlen($matched_body_start_tag);

回答1:

The problem is that your string have new lines where . in the pattern only matches single lines, you need to add /s modifier to make . to match multi-lines

Here is my solution, I prefer it this way.

<?php

$html=<<<EOD
<html>
<head>
</head>
<body buu="grger"     ga="Gag">
<p>Some text</p>
</body>
</html>
EOD;

    // get anything between <body> and </body> where <body can="have_as many" attributes="as required">
    if (preg_match('/(?:<body[^>]*>)(.*)<\/body>/isU', $html, $matches)) {
        $body = $matches[1];
    }
    // outputing all matches for debugging purposes
    var_dump($matches);
?>

Edit: I am updating my answer to provide you with better explanation why your code fails.

You have this string:

<html>
<head>
</head>
<body>
<p>Some text</p>
</body>
</html>

Everything seems to be fine with it but actually you have non-print characters (new line characters) on each line. You have 53 printable characters and 7 non printable (new lines, \n == 2 characters actually for each new line).

When you reach this part of the code:

$index_of_body_end_tag = strpos($html, '</body>');

You get the correct position of </body> (starting at position 51) but this counts the new lines.

So when you reach this line of code:

$index_of_body_start_tag + strlen($matched_body_start_tag)

It it evaluated to 31 (new lines included), and:

$index_of_body_end_tag - $index_of_body_start_tag + strlen($matched_body_start_tag)

It is evaluated to 51 - 25 + 6 = 32 (characters you have to read) but you only have 16 printable characters of text between <body> and </body> and 4 non printable characters (new line after <body> and new line before </body>). And here is the problem, you have to group the calculation (prioritize) like so:

$index_of_body_end_tag - ($index_of_body_start_tag + strlen($matched_body_start_tag))

evaluated to 51 - (25 + 6) = 51 - 31 = 20 (16 + 4).

:) Hope this helps you to understand why prioritizing is important. (Sorry for misleading you about newlines it is only valid in regex example I gave above).

回答2:

Personally, I wouldn't use regex.

<?php

$html = <<<EOD

<html>
    <head>
        <title>Example</title>
    </head>
    <body>
        <h1>foobar</h1>
    </body>
</html>

EOD;

$s = strpos($html, '<body>') + strlen('<body>');
$f = '</body>';

echo trim(substr($html, $s, strpos($html, $f) - $s));

?>

returns <h1>foobar</h1>

回答3:

The problem is in your substr computation of the ending index. You should substract all the way:

$index_of_body_end_tag - $index_of_body_start_tag - strlen($matched_body_start_tag)

But you are doing:

+ strlen($matched_body_start_tag)

That said, it seems a little overkill considering you can do it using preg_match only. You just need to make sure you match across new lines, using the s modifier:

preg_match('/<body[^>]*>(.*?)<\/body>/s', $html, $matches);
echo $matches[1];

Outputs:

<p>Some text</p>

回答4:

Somebodys probably already found your error, i didn't read all the replys.
The algebra is wrong.

code is here

Btw, first time seeing ideone.com, thats pretty cool.

$body = substr( 
          $html, 
          $index_of_body_start_tag + strlen($matched_body_start_tag),
          $index_of_body_end_tag - ($index_of_body_start_tag + strlen($matched_body_start_tag))
        );

or ..

$body = substr(
          $html,
          $index_of_body_start_tag + strlen($matched_body_start_tag),
          $index_of_body_end_tag - $index_of_body_start_tag - strlen($matched_body_start_tag)
       );

来源：https://stackoverflow.com/questions/4910975/extracting-the-body-text-of-an-html-document-using-php

标签

php

regex

text

text-processing

html-content-extraction