ConFoo Montreal 2017 Calling for Papers

Etiquetas de PHP

Cuando PHP analiza un fichero, busca las etiquetas de apertura y cierre, que son <?php y ?>, y que indican a PHP dónde empezar y finalizar la interpretación del código. Este mecanismo permite embeber a PHP en todo tipo de documentos, ya que todo lo que esté fuera de las etiquetas de apertura y cierre de PHP será ignorado por el analizador.

PHP también permite la etiqueta de apertura abreviada <? (la cual está desaconsejada debido a que sólo está disponible si se habilita con la directiva short_open_tag del fichero de configuración php.ini, o si PHP se configuró con la opción --enable-short-tags ).

Si un fichero contiene solamente código de PHP, es preferible omitir la etiqueta de cierre de PHP la final del mismo. Así se previene la adición de espacios en blanco o nuevas líneas accidentales después de la etiqueta de cierre, lo cual causaría efectos no deseados debido a que PHP comenzará la salida del búfer cuando no había intención por parte del programador de enviar ninguna salida en ese punto del script.

echo "Hola mundo";

// ... más código

echo "Última sentencia";

// el script finaliza aquí sin etiqueta de cierre de PHP

Historial de cambios
Versión Descripción
7.0.0 Se eliminaron de PHP las etiquetas de ASP <%, %>, <%=, y la etiqueta de script <script language="php">.
5.4.0 La etiqueta <?= siempre está disponible independientemente del ajuste ini short_open_tag.

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User Contributed Notes 5 notes

crazytonyi at gmail dot com
6 months ago
Regarding earlier note by @purkrt :

> I would like to stress out that the opening tag is "<?php[whitespace]", not just "<?php"

This is absolutely correct, but the wording may confuse some developers less familiar with the extent of the term "

Whitespace, in this context, would be any character that generated vertical or horizontal space, including tabs ( \t ), newlines ( \n ), and carriage returns ( \r ), as well as a space character ( \s ). So reusing purkrt's example:

<?php/*blah*/ echo "

would not work, as mentioned, but :

<?php /*php followed by space*/ echo "

will work, as well as :

/*php followed by end-of-line*/ echo "

and :

<?php    /*php followed by tab*/ echo "

I just wanted to clarify this to prevent anyone from misreading purkrt's note to mean that a the opening tag --even when being on its own line--required a space ( \s ) character. The following would work but is not at all necessary or how the earlier comment should be interpreted :

/*php followed by a space and end-of-line*/ echo "

The end-of-line character is whitespace, so it is all that you would need.
purkrt at gmail dot com
1 year ago
I would like to stress out that the opening tag is "<?php[whitespace]", not just "<?php". While this might seem blatantly obvious, I thought for some time that

<?php/*blah*/ echo "

would work, and it does not; the comment does not work as whitespace. I've run into this while converting some older code with short open tag.
jcastromail at yahoo dot es
7 months ago
Its important:

this code (for web)
    <? echo "am;" ?>

Generates the next result:
instead of
The last tag "?>" deletes the end of the line.

However, if we changed the line
    <? echo "am"; ?>
    <? echo "am"; ?>.  (or  a space)
then the result is :
1 year ago
A few related notes, partly covered elsewhere in the manual:

  → Since PHP 5.4 the inline echo <?= ?> short tags are always
    enabled regardless of the short_open_tag (php.ini) setting.

  → PHP tags are infrequently also referred to as open/close "tokens"
    (as per the tokenizers T_OPEN_TAG / _ECHO, and T_CLOSE_TAG naming).

  → The historic ASP-style <% %> and even more rarely used
    <script language=PHP></script> tags are to be repealed in PHP7.

There also exists a small tool called "phptags tidier" for consistently rewriting PHP short/long tags.  It's suitable to normalize include and template scripts, e.g. employ the always-enabled long <?php ?> tags, and/or relieve whitespace padding before/after PHP tags:

    phptags --long --whitespace --warn  *.php

Instead of reliably fixing the common whitespace/BOM issues around tags, it can also just remove all ?> close tags with `--unclose --tokenizer` as advised afore.
alexander dot podgorny at somewhere dot com
1 year ago
One reason to use long tags over short is to avoid confusion with <?xml ?> notation.
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