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从 HTML 中分离

当 PHP 解析一个文件时，会寻找开始和结束标记，标记告诉 PHP 开始和停止解释其中的代码。此种方式的解析可以使 PHP 嵌入到各种不同的文档中，凡是在一对开始和结束标记之外的内容都会被 PHP 解析器忽略。大多数情况下 PHP 都是嵌入在 HTML 文档中的，如下例所示。

<p>This is going to be ignored.</p>
<?php echo 'While this is going to be parsed.'; ?>
<p>This will also be ignored.</p>

还可以用更高级的结构：

Example #1 高级分离术

<?php
if ($expression) {
    ?>
    <strong>This is true.</strong>
    <?php
} else {
    ?>
    <strong>This is false.</strong>
    <?php
}
?>
上例可正常工作，因为当 PHP 碰到结束标记 ?> 时，就简单地将其后的内容原样输出（ 除非其后紧接着一个新行,参见指令分隔符 )直到碰到下一个开始标记为止。当然，上面的例子很做作，但是对输出大块的文本而言，脱离 PHP 解析模式通常比将所有内容用 echo() 或者 print() 输出更有效率。

可以在 PHP 中使用四对不同的开始和结束标记。其中两种，<?php ?> 和 <script language="php"> </script> 总是可用的。另两种是短标记和 ASP 风格标记，可以在 php.ini 配置文件中打开或关闭。尽管有些人觉得短标记和 ASP 风格标记很方便，但移植性较差，通常不推荐。

Note:

此外注意如果将 PHP 嵌入到 XML 或 XHTML 中则需要使用 <?php ?> 以保持符合标准。

Example #2 PHP 开始和结束标记

1.  <?php echo 'if you want to serve XHTML or XML documents, do like this'; ?>

2.  <script language="php">
        echo 'some editors (like FrontPage) don\'t
              like processing instructions';
    </script>

3.  <? echo 'this is the simplest, an SGML processing instruction'; ?>
    <?= expression ?> This is a shortcut for "<? echo expression ?>"

4.  <% echo 'You may optionally use ASP-style tags'; %>
    <%= $variable; # This is a shortcut for "<% echo . . ." %>

上例中的 1 和 2 总是可用的，其中 1 是最常用，并建议使用的。

短标记（上例 3）仅在通过 php.ini 配置文件中的指令 short_open_tag 打开后才可用，或者在 PHP 编译时加入了 --enable-short-tags 选项。

ASP 风格标记（上例 4）仅在通过 php.ini 配置文件中的指令 asp_tags 打开后才可用。

Note:

在以下情况应避免使用短标记：开发需要发行的程序或者库，或者在用户不能控制的服务器上开发。因为目标服务器可能不支持短标记。为了代码的移植及发行，确保不要使用短标记。

基本语法
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PHP手册
PHP手册 - N: 从 HTML 中分离

用户评论:

mike at clove dot com (30-Nov-2010 06:30)

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.

quickfur at quickfur dot ath dot cx (26-Jul-2010 10:40)

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 01:08)

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 07:56)

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.