Basic syntax

PHP/Basic syntax

PHP tags

When PHP parses a file, it looks for opening and closing tags, which are <?php and ?>  which tell PHP to start and stop interpreting the code between them. Parsing in this manner allows PHP to be embedded in all sorts of different documents, as everything outside of a pair of opening and closing tags is ignored by the PHP parser. PHP includes a short echo tag <?= which is a short-hand to the more verbose <?php echo.

Example

<?php echo 'if you want to serve PHP code in XHTML or XML documents,

                use these tags'; ?>

You can use the short echo tag to <?= 'print these values?>.

    It's equivalent to <?php echo 'print these values?>.

<? echo 'this code is within short tags, but will only work '.

            'if short_open_tag is enabled'; ?>

Short tags (example three) are available by default but can be disabled either via the short_open_tag php.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 maximize compatibility

If a file contains only 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

echo "Hello world";

// ... more code

echo "Last statement";

// 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:

<p>This is ignored by PHP and displayed by the browser. </p>

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

<p>This is 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 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

Example #1 Advanced escaping using conditions

<?php if ($expression == 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 echo "Hello World";?>

No newline

<?= "But newline now" ?>

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.

PHP Comments

There are two ways in which you can add comments to your PHP code. The first turns a single line (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 into a comment by preceding it with a pair of forward slashes, like this:

// This is a comment

You can also use this type of comment directly after a line of code to describe its action,
like this:

$x -= 5; // Decrement $x by 1

Multiple-line comments, there’s a second type of comment, you can use the /* and */ pairs of characters to open and close comments almost anywhere you like inside your code. Most, if not all, programmers use this construct to temporarily comment out entire sections of code that do not work or that, for one reason or another, they do not wish to be interpreted.

Example

<?php

/* This is a

multiline comments

that will not be

interpreted */

?>