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
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.
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 PHP code in XHTML or XML documents,
use these tags'; ?>
2. <script language="php">
echo 'some editors (like FrontPage) don\'t
like processing instructions within these tags';
3. <? echo 'this code is within short tags'; ?>
Code within these tags <?= 'some text' ?> is a shortcut for this code <? echo 'some text' ?>
4. <% echo 'You may optionally use ASP-style tags'; %>
Code within these tags <%= $variable; %> is a shortcut for this code <% 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
ASP style tags (example four) are only available when
they are enabled via the asp_tags php.ini
configuration file directive.
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.
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.
Starting with PHP 5.4, short echo tag <?= is always recognized and
valid, regardless of the short_open_tag setting.