PHP Velho Oeste 2024

Escaping from HTML

Everything outside of a pair of opening and closing tags is ignored by the PHP parser which allows PHP files to have mixed content. This allows PHP to be embedded in HTML documents, for example to create templates.

<p>This is going to be ignored by PHP and displayed by the browser.</p>
<?php echo 'While this is going to be parsed.'; ?>
<p>This will also be ignored by PHP and displayed by the browser.</p>
This works as expected, because when the PHP interpreter hits the ?> closing tags, it simply starts outputting whatever it finds (except for the immediately following newline - see instruction separation) until it hits another opening tag unless in the middle of a conditional statement in which case the interpreter will determine the outcome of the conditional before making a decision of what to skip over. See the next example.

Using structures with conditions

Example #1 Advanced escaping using conditions

<?php if ($expression == true): ?>
This will show if the expression is true.
<?php else: ?>
Otherwise this will show.
<?php endif; ?>
In this example PHP will skip the blocks where the condition is not met, even though they are outside of the PHP open/close tags; PHP skips them according to the condition since the PHP interpreter will jump over blocks contained within a condition that is not met.

For outputting large blocks of text, dropping out of PHP parsing mode is generally more efficient than sending all of the text through echo or print.

Note:

If PHP is embeded within XML or XHTML the normal PHP <?php ?> must be used to remain compliant with the standards.

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User Contributed Notes 4 notes

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383
quickfur at quickfur dot ath dot cx
13 years ago
When the documentation says that the PHP parser ignores everything outside the <?php ... ?> tags, it means literally EVERYTHING. Including things you normally wouldn't consider "valid", such as the following:

<html><body>
<p<?php if ($highlight): ?> class="highlight"<?php endif;?>>This is a paragraph.</p>
</body></html>

Notice how the PHP code is embedded in the middle of an HTML opening tag. The PHP parser doesn't care that it's in the middle of an opening tag, and doesn't require that it be closed. It also doesn't care that after the closing ?> tag is the end of the HTML opening tag. So, if $highlight is true, then the output will be:

<html><body>
<p class="highlight">This is a paragraph.</p>
</body></html>

Otherwise, it will be:

<html><body>
<p>This is a paragraph.</p>
</body></html>

Using this method, you can have HTML tags with optional attributes, depending on some PHP condition. Extremely flexible and useful!
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80
ravenswd at gmail dot com
14 years ago
One aspect of PHP that you need to be careful of, is that ?> will drop you out of PHP code and into HTML even if it appears inside a // comment. (This does not apply to /* */ comments.) This can lead to unexpected results. For example, take this line:

<?php
$file_contents
= '<?php die(); ?>' . "\n";
?>

If you try to remove it by turning it into a comment, you get this:

<?php
// $file_contents = '<?php die(); ?>' . "\n";
?>

Which results in ' . "\n"; (and whatever is in the lines following it) to be output to your HTML page.

The cure is to either comment it out using /* */ tags, or re-write the line as:

<?php
$file_contents
= '<' . '?php die(); ?' . '>' . "\n";
?>
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14
sgurukrupa at gmail dot com
9 years ago
Although not specifically pointed out in the main text, escaping from HTML also applies to other control statements:

<?php for ($i = 0; $i < 5; ++$i): ?>
Hello, there!
<?php endfor; ?>

When the above code snippet is executed we get the following output:

Hello, there!
Hello, there!
Hello, there!
Hello, there!
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-1
gazianis005 at gmail dot com
10 months ago
There are two types of escaping from HTML.
1.Normal escaping of using outside of a pair of opening and closing tag
2.Advance escaping of using conditions.

Example of normal escaping

<p>This is going to be ignored by the php parser and displayed by the browser</p>
<?php echo 'This is going to be parsed';?>
<>This will also ignored by the php parser and displayed by the browser</>

Example of advanced escaping

<?php if($expression == true): ?>
This will show if expression is true
<?php else : ?>
Otherwise this will show
<?php endif ;?>
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