WordPress API Reference | WordPress 3 Plugin Development Essentials

PHP functions

There are over 700 functions built into PHP. The following are seven that we used, with examples.

dirname

string dirname( string $path);

Returns parent directory's path. Often this is used to determine the path to the current script.

Example:

print dirname(__FILE__); // prints something like '/users/me'

file_get_contents

string file_get_contents( string $filename [, bool $use_include_path = false [, resource $context [, int $offset = -1 [, int $maxlen ]]]] )

Reads an entire file into a string. This is a useful way to read static, non-PHP files. It can even work for downloading remote files, but it's better to tie into the curl functions for serious downloading.

preg_match

int preg_match( string $pattern , string $subject [, array &$matches [, int $flags = 0 [, int $offset = 0 ]]] )

The preceding code performs a regular expression match using Perl-compatible regular expressions.

Example:

if ( preg_match('/^wp_/', $post_type) ){
   print 'Post type cannot begin with wp_';
}

Note

Special codes are used to signify different things:

^ = The beginning of the string.
$ = The end of the string.
[0-9] = Any digit, 0-9.
[a-z] = Any lowercase letter, a-z. You can make the search case-insensitive by using the "i" flag.
.* = Shorthand for any character.

preg_replace

mixed preg_replace('/[^a-z|_]/', '_', $sanitized['post_type']);

Performs a regular expression search and replaces using Perl-compatible regular expressions.

Example:

$string = 'The dog ate my homework';
$pattern = '/dog/i';
$replacement = 'bear';
echo preg_replace($pattern, $replacement, $string);

Returns:

"The bear ate my homework"

print_r

mixed print_r( mixed $expression [, bool $return = false ] )

Prints human-readable information about a variable. This is extremely useful for debugging.

Example:

$x = array( 'x' => 'Something',
       'y' => array('a' => 'alpha')
);
print_r($x);

Output:

Array
(
    [x] => Something
    [y] => Array
        (
            [a] => alpha
        )
   
)

sprintf

string sprintf( string $format [, mixed $args [, mixed $... ]] )

Returns a string produced according to the formatting string format. This function helps to avoid sloppy PHP concatenations. Mostly, we have used only the string types, marked by the %s placeholder, but there are others available. If your format string uses two or more placeholders, you can make use of the syntax for argument-swapping.

Example:

$format = 'The %1$s contains %2$s monkeys';
$output = sprintf($format, 'zoo', 'many');

strtolower

string strtolower( string $str )

Makes a string lowercase. This is a simple text formatting tool.

substr

string substr( string $string , int $start [, int $length ] )

Returns part of a string.

Example:

// Get the first 20 characters of a long string:
$short_str = substr($long_str, 0, 20);

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WordPress 3 Plugin Development Essentials

WordPress 3 Plugin Development Essentials

Overview of this book

PHP functions

dirname

file_get_contents

preg_match

Note

preg_replace

print_r

sprintf

strtolower

substr

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