Sintaxis básica
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.
Saliendo de HTML
Cuando PHP interpreta un fichero, buscar por las etiquetas de apertura y fin de bloque, que dicen a PHP donde empezar y finalizar la interpretación del código. Este mecanismo permite a PHP ser incrustado en todo tipo de documentos, todo lo que esté fuera de las etiquetas de PHP será ignorado por el interpretador. La mayoría de veces se encontrará con PHP incrustado en documentos HTML, como se muestra en este ejemplo.
<p>Este texto va a ser ignorado.</p>
<?php echo 'Mientras que esto va a ser interpretado.'; ?>
<p>Esto también será ignorado.</p>
También se pueden usar estructuras más avanzadas:
Example #1 Escapar de HTML avanzado
<?php
if ($expression) {
?>
<strong>This is true.</strong>
<?php
} else {
?>
<strong>This is false.</strong>
<?php
}
?>
Existen cuatro tipos de pares de etiquetas de apertura y de fin de bloque que se pueden usar en PHP. Dos de estas, <?php ?> y <script language="php"> </script>, siempre están disponibles. Las otras dos son etiquetas cortas y etiquetas estilo ASP y se pueden activar o desactivar desde el fichero de configuración php.ini Aunque para algunas personas las etiquetas cortas y etiquetas estilo ASP las encuentran más convenientes, son menos portables y generalmente no recomendadas.
Note:
Observe también que si se está incrustando PHP con XML o XHTML necesitará usar las etiquetas <?php ?> para seguir los estándares.
Example #2 Etiquetas de apertura y de fin de bloque de PHP
1. <?php echo 'si se quiere mostrar documentos XHTML o XML, debe hacerse así'; ?>
2. <script language="php">
echo 'algunos editores (como FrontPage) no les gusta
las instruciones de proceso';
</script>
3. <? echo 'esta es la forma más simple, una instrución de procesado SGML'; ?>
<?= expression ?> Esto es una forma corta para "<? echo expression ?>"
4. <% echo 'Quizá use de forma opcional etiquetas de estilo ASP'; %>
<%= $variable; # Esto es una forma corta para "<% echo . . ." %>
Las etiquetas vistas en los ejemplos uno y dos están siempre disponibles, el ejemplo uno es el más común y recomendado de los dos.
Las etiquetas cortas (ejemplo tres) están solo disponibles cuando se activan mediante la directiva short_open_tag en el fichero de configuración php.ini o si PHP se configuró con la opción --enable-short-tags .
Las etiquetas de estilo ASP (ejemplo cuatro) están solo disponibles cuando se activan mediante la directiva asp_tags en el fichero de configuración php.ini.
Note:
El uso de etiquetas cortas debe ser evitado cuando se desarrollan aplicaciones o librerias que están pensadas para su redistribución, o extender en servidores PHP que no están bajo su control, porque quizá las etiquetas cortas no están soportadas en un servidor determinado. Por portabilidad, redistribución de código, asegúrese no usar etiquetas cortas.
Note:
En PHP 5.2 y anteriores, no se permite que un fichero contenga únicamente la etiqueta de inicio de bloque <?php. En PHP 5.3 si se permite.
add a note
User Contributed Notes
Saliendo de HTML
mike at clove dot com
30-Nov-2010 06:30
quickfur at quickfur dot ath dot cx
26-Jul-2010 09:40
When the documentation says that the PHP parser ignores everything outside the <?php ... ?> tags, it means literally EVERYTHING. Including things you normally wouldn't consider "valid", such as the following:
<html><body>
<p<?php if ($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!
snor_007 at hotmail dot com
02-Apr-2010 12:28
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
%>
ravenswd at gmail dot com
02-Aug-2009 12:08
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";
?>
eksith at live dot com
02-Jul-2009 06:56
Even if it's pretty simple to insert echo lines to your PHP, I would storngly advise against it.
The safest way to output HTML content which may have special chraracters is to remove the HTML from your core code.
Put them in heredocs instead.
See the heredoc documentation and comments for more examples.
If you can remove as much of the HTML as you can from the rest of the PHP code (in terms of printf and echo lines), please do.
Try to keep your core logic and presentation separate.
<?php
$html =<<<HTML
<?xml version="1.0" encoding="UTF-8" ?>
... The rest of your HTML...
And a PHP {$variable} here and an array {$arr['value']} there.
HTML; // End of heredoc
// Print this HTML
echo $html
?>
Richard Neill
04-Apr-2009 03:26
WARNING: there is a potentially *nasty* gotcha here. Consider the following:
<html><body><pre>
First line <?/* Comment, inside PHP */?>
Second line
</pre></body></html>
If the comment is immediately followed by newline (and most editors will trim spaces at the ends of lines anyway), then you will NOT get what you expect.
Expect:
First line
Second Line
Actually get:
First line Second line
Now, if you are relying on that newline, for example to terminate a line of Javascript, where the trailing semicolon is optional, watch out!
david dot jarry at gmail dot com
26-Mar-2009 11:40
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?>
phpcoder at cyberpimp dot awmail dot org
10-Jan-2009 07:14
Some graphical HTML editors (and most web browsers) don't explicitly recognize the <?php ?> tags. When opening a PHP file with a graphical HTML editor to design the page layout, chunks of PHP code can appear as literal text if the PHP code contains a greater-than symbol (>).
Example:
<html>
<body>
Unsafe-<?php
if (4>3) {
echo "PHP-";
}
?>embedding
</body>
</html>
When executed, it should display this:
Unsafe-PHP-embedding
However, when opened with an HTML editor, the on-screen result might look like this:
Unsafe-3) { echo "PHP-"; } ?>embedding
...and further, the PHP code after the great-than operator (>) is at risk of being corrupted by the HTML editor's text formatting algorithms.
PHP code with greater-than symbols can be safely embedded into HTML by surrounding it with a pair of HTML-style comment delimiters + fake HTML end & start stags, as PHP-style comments.
Example:
<html>
<body>
Safe-<?php
/*><!--*/
if (4>3) {
echo "PHP-";
}
/*--><?*/
?>embedding
</body>
</html>
When executed, it should display this:
Safe-PHP-embedding
And when opened with an HTML editor (or even opened directly with a web browser), it should display this:
Safe-embedding
An HTML editor will see the surrounded PHP code as an HTML comment, and (hopefully) leave it as-is.
Finally, any PHP code with a hard-coded string containing the HTML end-of-comment delimiter (-->) should be reconstructed to be syntactically identical, while avoiding the literal "-->" sequence in the PHP code.
For example, this:
<?php
/*><!--*/
$a = "-->";
/*--><?*/
?>
...can safely be changed to any of these:
<?php
/*><!--*/
$a = "\55->";
/*--><?*/
?>
<?php
/*><!--*/
$a = "--\76";
/*--><?*/
?>
<?php
/*><!--*/
$a = '--'.'>';
/*--><?*/
?>
admin at furutsuzeru dot net
02-Jan-2009 04:50
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.