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Basic syntax

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When PHP processes a file, it recognizes the opening and closing tags, <?php and ?>, to define the boundaries of PHP code execution. Content outside these tags is ignored by the PHP parser, allowing PHP to seamlessly embed in various document types.

PHP tags

When PHP processes a file, it recognizes the opening and closing tags, <?php and ?>, to define the boundaries of PHP code execution. Content outside these tags is ignored by the PHP parser, allowing PHP to seamlessly embed in various document types.

A whitespace character (space, tab, or newline) must follow <?php to ensure proper token separation. Omitting this whitespace will result in a syntax error.

PHP also includes the short echo tag <?=, which is shorthand for <?php echo.

PHP Opening and Closing Tags

php

1.  <?php echo 'if you want to serve PHP code in XHTML or XML documents,
                use these tags'; ?>

2.  You can use the short echo tag to <?= 'print this string' ?>.
    It's equivalent to <?php echo 'print this string' ?>.

3.  <? echo 'this code is within short tags, but will only work '.
            'if short_open_tag is enabled'; ?>

Short tags (the third line in the example above) are available by default but can be disabled either via the short_open_tag Ini configuration file directive, or are disabled by default if PHP is built with the --disable-short-tags configuration.

Note

As short tags can be disabled it is recommended to only use the normal tags (<?php ?> and <?= ?>) to maximise compatibility.

If a file ends with PHP code, it is preferable to omit the PHP closing tag at the end of the file. This prevents accidental whitespace or new lines being added after the PHP closing tag, which may cause unwanted effects because PHP will start output buffering when there is no intention from the programmer to send any output at that point in the script.

PHP Code Only File

php

<?php
echo "Hello world\n";

// ... more code

echo "Last statement\n";

// the script ends here with no PHP closing tag

Escaping from HTML

Everything outside of a pair of opening and closing tags is ignored by the PHP parser which allows PHP files to have mixed content. This allows PHP to be embedded in HTML documents, for example to create templates.

Embedding PHP in HTML

php

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

This works as expected, because when the PHP interpreter hits the ?> closing tags, it simply starts outputting whatever it finds (except for the immediately following newline - see instruction separation) until it hits another opening tag unless in the middle of a conditional statement in which case the interpreter will determine the outcome of the conditional before making a decision of what to skip over. See the next example.

Using structures with conditions

Advanced escaping using conditions

php

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

In this example PHP will skip the blocks where the condition is not met, even though they are outside of the PHP open/close tags; PHP skips them according to the condition since the PHP interpreter will jump over blocks contained within a condition that is not met.

For outputting large blocks of text, dropping out of PHP parsing mode is generally more efficient than sending all of the text through echo() or print().

Note

If PHP is embedded within XML or XHTML the normal PHP <?php ?> must be used to remain compliant with the standards.

Instruction separation

As in C or Perl, PHP requires instructions to be terminated with a semicolon at the end of each statement. The closing tag of a block of PHP code automatically implies a semicolon; you do not need to have a semicolon terminating the last line of a PHP block. The closing tag for the block will include the immediately trailing newline if one is present.

Example showing the closing tag encompassing the trailing newline

php

<?php echo "Some text"; ?>
No newline
<?= "But newline now" ?>

The above example will output:

output

Some textNo newline
But newline now

Examples of entering and exiting the PHP parser

php

<?php
    echo "This is a test\n";
?>

<?php echo "This is a test\n" ?>

<?php echo "We omitted the last closing tag\n";

Note

The closing tag of a PHP block at the end of a file is optional, and in some cases omitting it is helpful when using include() or require(), so unwanted whitespace will not occur at the end of files, and you will still be able to add headers to the response later. It is also handy if you use output buffering, and would not like to see added unwanted whitespace at the end of the parts generated by the included files.

Comments

PHP supports 'C', 'C++' and Unix shell-style (Perl style) comments. For example:

Comments

php

<?php
    echo "This is a test\n"; // This is a one-line c++ style comment
    /* This is a multi line comment
       yet another line of comment */
    echo "This is yet another test\n";
    echo "One Final Test\n"; # This is a one-line shell-style comment
?>

The "one-line" comment styles only comment to the end of the line or the current block of PHP code, whichever comes first. This means that HTML code after // ... ?> or # ... ?> WILL be printed: ?> breaks out of PHP mode and returns to HTML mode, and // or # cannot influence that.

One Line Comments

php

<h1>This is an <?php # echo 'simple';?> example</h1>
<p>The header above will say 'This is an  example'.</p>

'C' style comments end at the first */ encountered. Make sure you don't nest 'C' style comments. It is easy to make this mistake if you are trying to comment out a large block of code.

php

<?php
 /*
    echo 'This is a test'; /* This comment will cause a problem */
 */
?>

Source: language/basic-syntax.xml · from the official PHP manual (php/doc-en)