從 HTML 中跳脫

當 PHP 解析一個文件時,會尋找開始和結束標籤,標籤告訴 PHP 開始和停止解釋其中的代碼。此種方式的解析可以使 PHP 嵌入到各種不同的文件中,凡是在一對開始和結束標籤之外的內容都會被 PHP 解析器忽略。大多數情況下 PHP 都是嵌入在 HTML 文件中的,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>

還可以用更進階的結構:

Example #1 進階跳脫

<?php
if ($expression) {
    
?>
    <strong>This is true.</strong>
    <?php
} else {
    
?>
    <strong>This is false.</strong>
    <?php
}
?>
上例可正常工作,因為當 PHP 碰到結束標籤 ?> 時,就簡單地將其後的內容原封不動輸出直到碰到下一個開始標籤為止。當然,上面的例子很做作,但是對輸出大區塊的文本而言,跳脫 PHP 解析模式通常比將所有內容用 echo 或者 print 輸出更有效率。

可以在 PHP 中使用四對不同的開始和結束標籤。其中兩種,<?php ?> 和 <script language="php"> </script> 總是可用的。另兩種是短標籤和 ASP 風格標籤,可以在 php.ini 配置文件中打開或關閉。儘管有些人覺得短標籤和 ASP 風格標籤很方便,但移植性較差,通常不推薦。

Note:

此外注意如果將 PHP 嵌入到 XML 或 XHTML 中則需要使用 <?php ?> 以保持符合標準。

Example #2 PHP 開始和結束標籤

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 總是可用的,其中 1 是最常用,並建議使用的。

短標籤(上例 3)僅在通過 php.ini 配置文件中的指令 short_open_tag 打開後才可用,或者在 PHP 編譯時加入了 --enable-short-tags 選項。

Note:

如果用 PHP 3 還可以通過 short_tags() 函式使用短標籤。此方法只適用於 PHP 3!

ASP 風格標籤(上例 4)僅在通過 php.ini 設定文件中的指令 asp_tags 打開後才可用。

Note:

ASP 風格標籤的支援是 3.0.4 版添加的。

Note:

在以下情況應避免使用短標籤:開發需要發行的程序或者函式庫,或者在用戶不能控制的伺服器上開發。因為目標伺服器可能不支持短標籤。為了代碼的移植及發行,確保不要使用短標籤。

add a note add a note

User Contributed Notes 11 notes

up
392
quickfur at quickfur dot ath dot cx
13 years ago
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!
up
76
ravenswd at gmail dot com
14 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";
?>
up
34
sgurukrupa at gmail dot com
10 years ago
Although not specifically pointed out in the main text, escaping from HTML also applies to other control statements:

<?php for ($i = 0; $i < 5; ++$i): ?>
Hello, there!
<?php endfor; ?>

When the above code snippet is executed we get the following output:

Hello, there!
Hello, there!
Hello, there!
Hello, there!
up
4
davidhcefx
3 years ago
When the PHP interpreter hits the ?> closing tags, it WON'T output right away if it's inside of a conditional statement:
(no matter if it's an Alternative Syntax or not)

<html>
<?php
$a
= 1;
$b = 2;
if (
$a === 1) {
    if (
$b == 2) {
       
?><head></head><?php
   
} else {
       
?><body></body><?php
   
}
}
?>
</html>

This would output `<html><head></head></html>`.
Aside from conditional statements, the PHP interpreter also skip over functions! What a surprise!

<html>
<?php
function show($a) {
   
?>
    <a href="https://www.<?php echo $a ?>.com">
    Link
    </a>
    <?php
}
?>
<body>
    <?php show("google") ?>
</body>
</html>

This gives `<html><body><a href="https://www.google.com">Link</a></body></html>`.
These really confused me, because at first I thought it would output any HTML code right away, except for Alternative Syntaxes (https://www.php.net/manual/en/control-structures.alternative-syntax.php). There are more strange cases than I thought.
up
6
anisgazig at gmail dot com
4 years ago
Version of  7.0.0,3 tags are available in php.
1.long form tag (<?php ?>)
2.short echo tag(<?= ?>)
3.short_open_tag(? ?)
You can use short_open_tag when you start xml with php.
up
27
snor_007 at hotmail dot com
13 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
%>
up
-6
mike at clove dot com
13 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.
up
-10
Emil Cataranciuc
5 years ago
"<script language="php"> </script>, are always available." since PHP 7.0.0 is no longer true. These are removed along the ASP "<%, %>, <%=" tags.
up
-3
Anonymous
3 years ago
Since it's not documented (AFAICT) and it might cause confusion: a single line break immediately after ?> is ignored. Since whitespace is hard to see, whitespace is replaced with _ and the following code

<?php echo '1'; ?>
<?php
echo '2'; ?>_
<?php echo '3'; ?>
_<?php echo '4'; ?>_<?php echo '5'; ?>

will produce

12_
3_4_5
up
-8
anisgazig.com
3 years ago
<p>This is ignore by the php parser and displayed by the browser </p>

<?php echo "While this is going to be parsed"; ?>

<?php

when php interpreter hits the closing tag it start to outputing everything whatever it finds until it hit another opening tag
.If php interpreter find a conditional statement in the middle of a block then php interpreter decided which block skip 

Advanced escaping using conditions

 
<?php $a = 10; if($a<100): ?>
  This conditional block is executed
  <?php else: ?>
      otherwise this will be executed
      <?php endif; ?>

In php 5 version,there are 5 opening and closing tags.
1.<?php echo "standard long form php tag and if you use xml with php this tag will be use";?>

2.<?= "short echo tag and alwayes available from 5.4.0";?>

3.<? echo "short open tag which is available if short_open_tag is enable in php ini configuration file directive or php was configured with --enable-short-tags.This tag has discoursed from php 7.If you want to use xml with php,then short_open_tag in php ini will be disabled";?>

4.<script language="php">
echo "Some editor do not like processing the code within this tag and this tag is removed from php 7.0.0 version";

</script>

5.<% echo "asp style tag and asp_tags should be enabled but now php 7.0.0 version,this tag is removed";%>
up
-56
admin at furutsuzeru dot net
15 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.
To Top