Etiquetas de PHP
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 $highlight is true, then the output will be:
<html><body>
<p class="highlight">This is a paragraph.</p>
</body></html>
Otherwise, it will be:
<html><body>
<p>This is a paragraph.</p>
</body></html>
Using this method, you can have HTML tags with optional attributes, depending on some PHP condition. Extremely flexible and useful!
Salir de HTML
Cualquier cosa fuera del par de etiquetas de apertura y cierre es ignorado por el intérprete de PHP, el cual permite que los ficheros de PHP tengan contenido mixto. Esto permite que PHP sea embebido en documentos HTML para, por ejemplo, crear plantillas.
<p>Esto va a ser ignorado por PHP y mostrado por el navegador.</p>
<?php echo 'Mientras que esto va a ser interpretado.'; ?>
<p>Esto también será ignorado por PHP y mostrado por el navegador.</p>
Usar estructuras con condiciones
Ejemplo #1 Salida avanzada usando condiciones
<?php if ($expresión == true): ?>
Esto se mostrará si la expresión es verdadera.
<?php else: ?>
En caso contrario se mostrará esto.
<?php endif; ?>
Para imprimir bloques de texto grandes, es más eficiente abandonar el modo intérprete de PHP que enviar todo el texto a través de echo o print.
Existen cuatro tipos de pares de etiquetas de apertura y de cierre que se pueden usar en PHP. Dos de estas, <?php ?> y <script language="php"> </script>, siempre están disponibles. Las otras dos son las etiquetas abreviadas y las etiquetas estilo ASP, que se pueden activar o desactivar desde el fichero de configuración php.ini Aunque algunas personas encuentran las etiquetas abreviadas y las etiquetas estilo ASP más convenientes, son menos portables y generalmente no se recomiendan.
Nota:
Observe también que si se está incrustando PHP dentro de XML o XHTML necesitará usar las etiquetas <?php ?> para seguir los estándares.
Ejemplo #2 Etiquetas de apertura y de cierre 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'; ?>
<?= expresión ?> Esto es una forma abreviada de "<? echo expresión ?>"
4. <% echo 'Quizá use de forma opcional etiquetas de estilo ASP'; %>
<%= $variable; # Esto es una forma abreviada de "<% 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 abreviadas (ejemplo tres) están solo disponibles cuando se activan mediante la directiva short_open_tag del 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 del fichero de configuración php.ini.
Nota:
Se debe evitar el uso de etiquetas abreviadas cuando se desarrollen aplicaciones o bibliotecas que estén pensadas para su redistribución o despliegue en servidores PHP que no estén bajo su control, porque puede que las etiquetas abreviadas no estén soportadas en un servidor determinado. Por portabilidad y código redistribuible, asegúrese de no usar etiquetas abreviadas.
Nota:
En PHP 5.2 y anteriores, el intérprete no permite que un fichero contenga únicamente la etiqueta de apertura <?php. A partir de PHP 5.3 sí se permite siempre que existan uno o más caracteres espacio en blanco después de la etiqueta de apertura.
Nota:
Desde PHP 5.4, la etiqueta abreviada de echo <?= siempre es reconocida y válida, sin tener en cuenta la configuración de short_open_tag.
add a note
User Contributed Notes
Salir de HTML - [9 notes]
quickfur at quickfur dot ath dot cx ¶
2 years ago
snor_007 at hotmail dot com ¶
3 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
%>
david dot jarry at gmail dot com ¶
4 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?>
mike at clove dot com ¶
2 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.
ravenswd at gmail dot com ¶
3 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";
?>
admin at furutsuzeru dot net ¶
4 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.
Richard Neill ¶
4 years ago
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!
phpcoder at cyberpimp dot awmail dot org ¶
4 years ago
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 = '--'.'>';
/*--><?*/
?>
eksith at live dot com ¶
3 years ago
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
?>