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>
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 PHP 5, there are up to five different pairs of opening and closing tags
available in PHP, depending on how PHP is configured. Two of these,
<?php ?> and
<script language="php"> </script>, are always
available. There is also the short echo tag
which is always available in PHP 5.4.0 and later.
The other two are short tags and ASP style tags. 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.
PHP 7 removes support for ASP tags and
<script language="php"> tags. As such, we recommend
<?php ?> and
<?= ?> when
writing PHP code to maximise compatibility.
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. You can use the short echo tag to <?= 'print this string' ?>.
It's always enabled in PHP 5.4.0 and later, and is equivalent to
<?php echo 'print this string' ?>.
3. <? echo 'this code is within short tags, but will only work '.
'if short_open_tag is enabled'; ?>
4. <script language="php">
echo 'some editors (like FrontPage) don\'t
like processing instructions within these tags';
This syntax is removed in PHP 7.0.0.
5. <% echo 'You may optionally use ASP-style tags'; %>
Code within these tags <%= $variable; %> is a shortcut for this code <% echo $variable; %>
Both of these syntaxes are removed in PHP 7.0.0.
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 five) are only available when they are enabled via the asp_tags php.ini configuration file directive, and have been removed in PHP 7.0.0.
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.