PHP: HTML からの脱出

HTML からの脱出

PHP のパーサは、開始タグと終了タグに囲まれていない部分をすべて無視します。そのおかげで、PHP のファイルにそれ以外のコンテンツを混在させることができるのです。たとえば PHP を HTML ドキュメントに組み込んで、テンプレートを作ったりすることもできます。

<p>この部分は PHP から無視され、そのままブラウザには表示されます。</p>
<?php echo '一方、この部分はパースされます。'; ?>
<p>この部分も PHP から無視され、そのままブラウザには表示されます。</p>

これは期待通りに動作します。なぜなら、PHP インタプリタは ?> 終了タグを見つけるとそれ以降新たに開始タグを見つけるまでの内容を何でも出力するからです (終了タグの直後の改行は別です。命令の分離を参照ください)。しかし、PHP が条件文の中にいる場合は話が別です。その場合は、まず条件式の結果を判定してから何をスキップするかを判断します。次の例を参照ください。

条件文を使った例です。

例1 条件文を使った高度な脱出

<?php if ($expression == true): ?>
  条件式が真の場合にこれが表示されます。
<?php else: ?>
  それ以外の場合にこちらが表示されます。
<?php endif; ?>

この例では、PHP は条件を満たさないブロックを処理しません。たとえそれが PHP の開始タグと終了タグに囲まれた部分でなくても、条件文にしたがってそこを読み飛ばします。というのも、PHP のインタプリタは条件を満たさない箇所をブロックごと読み飛ばすからです。

大量のテキストを出力する際に echo や print を用いることを考えると、このように一度 PHP のパースモードを抜けるほうが効率的です。

PHP コードを XML や XHTML に埋め込む場合には、標準規格に従うために <?php ?> タグを使用する必要があるでしょう。

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User Contributed Notes 12 notes

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384

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!

down

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";
?>

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gazianis005 at gmail dot com ¶

5 months ago

There are two types of escaping from HTML.
1.Normal escaping of using  outside of a pair of opening and closing tag
2.Advance escaping of  using conditions.

Example of normal escaping

<p>This is  going to be ignored by the php parser and displayed by the browser</p>
<?php echo 'This is going to be parsed';?>
<>This will also ignored by the php parser and displayed by the browser</> 

Example of  advanced escaping 

<?php if($expression == true): ?>
This will show if expression is true
<?php else : ?>
Otherwise  this will show
<?php endif ;?>

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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
%>

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sgurukrupa at gmail dot com ¶

9 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!

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-2

anisgazig at gmail dot com ¶

3 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.

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-3

bryanrojasq.wordpress.com ¶

1 year ago

Example for a basic implementation of ternary operator to validate and print a class in the layout.

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <title><?= $page_title ?></title>
</head>
<body <?= strtolower($page_slug) === 'homepage' ? 'class="page-homepage"' : ''; ?>>
    <section>
        <h1><?= $page_title ?></h1>
        <p>This is a paragraph.</p>
    </section>
</body>
</html>

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-6

mike at clove dot com ¶

12 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.

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-23

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.

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-19

Anonymous ¶

2 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

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-28

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";%>

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-51

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.

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