Some parts of the WordPress code structure for PHP markup are inconsistent in their style. WordPress is working to gradually improve this by helping users maintain a consistent style so the code can become clean and easy to read at a glance.

Keep the following points in mind when writing PHP code for WordPress, whether for core programming code, plugins, or themes. The guidelines are similar to Pear standards in many ways, but differ in some key respects.

See also: PHP Documentation Standards.

PHP #

Single and Double Quotes #

Use single and double quotes when appropriate. If you’re not evaluating anything in the string, use single quotes. You should almost never have to escape quotes in a string, because you can just alternate your quoting style, like so:

echo '<a href="/static/link" title="Yeah yeah!">Link name</a>';
echo "<a href='$link' title='$linktitle'>$linkname</a>";

Text that goes into attributes should be run through esc_attr() so that single or double quotes do not end the attribute value and invalidate the HTML and cause a security issue. See Data Validation in the Codex for further details.

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Indentation #

Your indentation should always reflect logical structure. Use real tabs and not spaces, as this allows the most flexibility across clients.

Exception: if you have a block of code that would be more readable if things are aligned, use spaces:

[tab]$foo   = 'somevalue';
[tab]$foo2  = 'somevalue2';
[tab]$foo34 = 'somevalue3';
[tab]$foo5  = 'somevalue4';

For associative arrays, values should start on a new line. Note the comma after the last array item: this is recommended because it makes it easier to change the order of the array, and makes for cleaner diffs when new items are added.

$my_array = array(
[tab]'foo'   => 'somevalue',
[tab]'foo2'  => 'somevalue2',
[tab]'foo3'  => 'somevalue3',
[tab]'foo34' => 'somevalue3',
);

Rule of thumb: Tabs should be used at the beginning of the line for indentation, while spaces can be used mid-line for alignment.

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Brace Style #

Braces shall be used for all blocks in the style shown here:

if ( condition ) {
	action1();
	action2();
} elseif ( condition2 && condition3 ) {
	action3();
	action4();
} else {
	defaultaction();
}

Furthermore, if you have a really long block, consider whether it can be broken into two or more shorter blocks or functions. If you consider such a long block unavoidable, please put a short comment at the end so people can tell at glance what that ending brace ends – typically this is appropriate for a logic block, longer than about 35 rows, but any code that’s not intuitively obvious can be commented.

Braces should always be used, even when they are not required:

if ( condition ) {
	action0();
}

if ( condition ) {
	action1();
} elseif ( condition2 ) {
	action2a();
	action2b();
}

foreach ( $items as $item ) {
	process_item( $item );
}

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Regular Expressions #

Perl compatible regular expressions (PCRE, preg_ functions) should be used in preference to their POSIX counterparts. Never use the /e switch, use preg_replace_callback instead.

It’s most convenient to use single-quoted strings for regular expressions since, contrary to double-quoted strings, they have only two metasequences: \' and \\.

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No Shorthand PHP Tags #

Important: Never use shorthand PHP start tags. Always use full PHP tags.

Correct:

<?php ... ?>
<?php echo $var; ?>

Incorrect:

<? ... ?>
<?= $var ?>

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Remove Trailing Spaces #

Remove trailing whitespace at the end of each line of code. Omitting the closing PHP tag at the end of a file is preferred. If you use the tag, make sure you remove trailing whitespace.

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Space Usage #

Always put spaces after commas, and on both sides of logical, comparison, string and assignment operators.

x == 23
foo && bar
! foo
array( 1, 2, 3 )
$baz . '-5'
$term .= 'X'

Put spaces on both sides of the opening and closing parenthesis of if, elseif, foreach, for, and switch blocks.

foreach ( $foo as $bar ) { ...

When defining a function, do it like so:

function my_function( $param1 = 'foo', $param2 = 'bar' ) { ...

When calling a function, do it like so:

my_function( $param1, func_param( $param2 ) );

When performing logical comparisons, do it like so:

if ( ! $foo ) { ...

When type casting, do it like so:

foreach ( (array) $foo as $bar ) { ...

$foo = (boolean) $bar;

When referring to array items, only include a space around the index if it is a variable, for example:

$x = $foo['bar']; // correct
$x = $foo[ 'bar' ]; // incorrect

$x = $foo[0]; // correct
$x = $foo[ 0 ]; // incorrect

$x = $foo[ $bar ]; // correct
$x = $foo[$bar]; // incorrect

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Formatting SQL statements #

When formatting SQL statements you may break it into several lines and indent if it is sufficiently complex to warrant it. Most statements work well as one line though. Always capitalize the SQL parts of the statement like UPDATE or WHERE.

Functions that update the database should expect their parameters to lack SQL slash escaping when passed. Escaping should be done as close to the time of the query as possible, preferably by using $wpdb->prepare()

$wpdb->prepare() is a method that handles escaping, quoting, and int-casting for SQL queries. It uses a subset of the sprintf() style of formatting. Example :

$var = "dangerous'"; // raw data that may or may not need to be escaped
$id = some_foo_number(); // data we expect to be an integer, but we're not certain

$wpdb->query( $wpdb->prepare( "UPDATE $wpdb->posts SET post_title = %s WHERE ID = %d", $var, $id ) );

%s is used for string placeholders and %d is used for integer placeholders. Note that they are not ‘quoted’! $wpdb->prepare() will take care of escaping and quoting for us. The benefit of this is that we don’t have to remember to manually use esc_sql(), and also that it is easy to see at a glance whether something has been escaped or not, because it happens right when the query happens.

See Data Validation in the Codex for more information.

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Database Queries #

Avoid touching the database directly. If there is a defined function that can get the data you need, use it. Database abstraction (using functions instead of queries) helps keep your code forward-compatible and, in cases where results are cached in memory, it can be many times faster.

If you must touch the database, get in touch with some developers by posting a message to the wp-hackers mailing list. They may want to consider creating a function for the next WordPress version to cover the functionality you wanted.

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Naming Conventions #

Use lowercase letters in variable, action, and function names (never camelCase). Separate words via underscores. Don’t abbreviate variable names un-necessarily; let the code be unambiguous and self-documenting.

function some_name( $some_variable ) { [...] }

Class names should use capitalized words separated by underscores. Any acronyms should be all upper case.

class Walker_Category extends Walker { [...] }
class WP_HTTP { [...] }

Constants should be in all upper-case with underscores separating words:

define( 'DOING_AJAX', true );

Files should be named descriptively using lowercase letters. Hyphens should separate words.

my-plugin-name.php

Class file names should be based on the class name with class- prepended and the underscores in the class name replaced with hyphens, for example WP_Error becomes:

class-wp-error.php

This file-naming standard is for all current and new files with classes. There is one exception for three files that contain code that got ported into BackPress: class.wp-dependencies.php, class.wp-scripts.php, class.wp-styles.php. Those files are prepended with class., a dot after the word class instead of a hyphen.

Files containing template tags in wp-includes should have -template appended to the end of the name so that they are obvious.

general-template.php

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Self-Explanatory Flag Values for Function Arguments #

Prefer string values to just true and false when calling functions.

// Incorrect
function eat( $what, $slowly = true ) {
...
}
eat( 'mushrooms' );
eat( 'mushrooms', true ); // what does true mean?
eat( 'dogfood', false ); // what does false mean? The opposite of true?

Since PHP doesn’t support named arguments, the values of the flags are meaningless, and each time we come across a function call like the examples above, we have to search for the function definition. The code can be made more readable by using descriptive string values, instead of booleans.

// Correct
function eat( $what, $speed = 'slowly' ) {
...
}
eat( 'mushrooms' );
eat( 'mushrooms', 'slowly' );
eat( 'dogfood', 'quickly' );

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Ternary Operator #

Ternary operators are fine, but always have them test if the statement is true, not false. Otherwise, it just gets confusing. (An exception would be using ! empty(), as testing for false here is generally more intuitive.)

For example:

// (if statement is true) ? (do this) : (else, do this);
$musictype = ( 'jazz' == $music ) ? 'cool' : 'blah';
// (if field is not empty ) ? (do this) : (else, do this);

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Yoda Conditions #

if ( true == $the_force ) {
	$victorious = you_will( $be );
}

When doing logical comparisons, always put the variable on the right side, constants or literals on the left.

In the above example, if you omit an equals sign (admit it, it happens even to the most seasoned of us), you’ll get a parse error, because you can’t assign to a constant like true. If the statement were the other way around ( $the_force = true ), the assignment would be perfectly valid, returning 1, causing the if statement to evaluate to true, and you could be chasing that bug for a while.

A little bizarre, it is, to read. Get used to it, you will.

This applies to ==, !=, ===, and !==. Yoda conditions for <, >, <= or >= are significantly more difficult to read and are best avoided.

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Clever Code #

In general, readability is more important than cleverness or brevity.

isset( $var ) || $var = some_function();

Although the above line is clever, it takes a while to grok if you’re not familiar with it. So, just write it like this:

if ( ! isset( $var ) ) {
	$var = some_function();
}

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Error Control Operator @ #

As noted in the PHP docs:

PHP supports one error control operator: the at sign (@). When prepended to an expression in PHP, any error messages that might be generated by that expression will be ignored.

While this operator does exist in Core, it is often used lazily instead of doing proper error checking. Its use is highly discouraged, as even the PHP docs also state:

Warning: Currently the “@” error-control operator prefix will even disable error reporting for critical errors that will terminate script execution. Among other things, this means that if you use “@” to suppress errors from a certain function and either it isn’t available or has been mistyped, the script will die right there with no indication as to why.

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Credits #

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Major Changes #