PHP Unconference Europe 2015

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 an 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 what 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.

There are four different pairs of opening and closing tags which can be used in PHP. Two of those, <?php ?> and <script language="php"> </script>, are always available. The other two are short tags and ASP style tags, and can be turned on and off from the php.ini configuration file. As such, while some people find short tags and ASP style tags convenient, they are less portable, and generally not recommended.

Note:

Also note that if you are embedding PHP within XML or XHTML you will need to use the <?php ?> tags to remain compliant with standards.

Example #2 PHP Opening and Closing Tags

1.  <?php echo 'if you want to serve XHTML or XML documents, do it like this'?>

2.  <script language="php">
        
echo 'some editors (like FrontPage) don\'t
              like processing instructions'
;
    
</script>

3.  <? echo 'this is the simplest, an SGML processing instruction'?>
    <?= expression ?> This is a shortcut for "<? echo expression ?>"

4.  <% echo 'You may optionally use ASP-style tags'; %>
    <%= $variable; %> This is a shortcut for "<% echo $variable; %>"

While the tags seen in examples one and two are both always available, example one is the most commonly used, and recommended, of the two.

Short tags (example three) are only available when they are enabled via the short_open_tag php.ini configuration file directive, or if PHP was configured with the --enable-short-tags option.

ASP style tags (example four) are only available when they are enabled via the asp_tags php.ini configuration file directive.

Note:

Using short tags should be avoided when developing applications or libraries that are meant for redistribution, or deployment on PHP servers which are not under your control, because short tags may not be supported on the target server. For portable, redistributable code, be sure not to use short tags.

Note:

In PHP 5.2 and earlier, the parser does not allow the <?php opening tag to be the only thing in a file. This is allowed as of PHP 5.3 provided there are one or more whitespace characters after the opening tag.

Note:

Starting with PHP 5.4, short echo tag <?= is always recognized and valid, regardless of the short_open_tag setting.

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User Contributed Notes 8 notes

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102
quickfur at quickfur dot ath dot cx
4 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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39
ravenswd at gmail dot com
5 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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1
Kalimuthu
1 month ago
One more disadvantage of using PHP short tags is that, it clashes with XML. Because XML also uses <? to open code blocks. See below sample XML code

<?xml version="1.0" encoding="UTF-8"?>
<note>
    <to> Tove</to>
    <from>Jani</from>
    <heading>Reminder</heading>
    <body>Don't forget me this weekend!</body>
</note>
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10
sgurukrupa at gmail dot com
7 months 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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12
mike at clove dot com
3 years ago
It's possible to write code to create php escapes which can be processed later by substituting \x3f for '?' - as in echo "<\x3fphp echo 'foo'; \x3f>";

This is useful for creating a template parser which later is rendered by PHP.
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11
snor_007 at hotmail dot com
4 years ago
Playing around with different open and close tags I discovered you can actually mix different style open/close tags

some examples

<%
//your php code here
?>

or

<script language="php">
//php code here
%>
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6
david dot jarry at gmail dot com
5 years ago
Shorts tags and ASP tags are unportables and should be avoided.

<script /> tags are a waste of time and simply inefficient in some simple cases :
<body>
  <p style="color: <script language="php"> echo $text_color </script>;">
  (...) VERY long text (...)
  </p>
</body>
To render this example in a basic XHTML editor, you need to "echo()" all the content or break the XML rules.

The solution seems obvious to me : Why not add the shortcut "<?php= ?>" to be used within XML and XHTML documents ?
<?php='example1'?>
<?php
=$example2?>
up
0
admin at furutsuzeru dot net
5 years ago
These methods are just messy. Short-opening tags and ASP-styled tags are not always enabled on servers. The <script language="php"></script> alternative is just out there. You should just use the traditional tag opening:

<?php?>

Coding islands, for example:

<?php
$me
'Pyornide';
?>
<?=$me
;?> is happy.
<?php
$me
= strtoupper($me);
?>
<?=$me
;?> is happier.

Lead to something along the lines of messy code. Writing your application like this can just prove to be more of an
inconvenience when it comes to maintenance.

If you have to deal chunks of HTML, then consider having a templating system do the job for you. It is a poor idea to rely on the coding islands method as a template system in any way, and for reasons listed above.
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