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If you are new to PHP or just need to refresh your skills, this is the place to start. This series of tutorials will give you the basic knowledge you will need to create a simple PHP website.
PHP is a reflective programming language originally designed for producing dynamic web pages.[1] PHP is used mainly in server-side scripting, but can be used from a command line interface or in standalone graphical applications. Textual User Interfaces can also be created using ncurses.
The require_once() statement includes and evaluates the specified file during the execution of the script. This is a behavior similar to the require() statement, with the only difference being that if the code from a file has already been included, it will not be included again. See the documentation for require() for more information on how this statement works.
require_once() should be used in cases where the same file might be included and evaluated more than once during a particular execution of a script, and you want to be sure that it is included exactly once to avoid problems with function redefinitions, variable value reassignments, etc.
For examples on using require_once() and include_once(), look at the PEAR code included in the latest PHP source code distributions.
Return values are the same as with include(). If the file was already included, this function returns TRUE
Note: require_once() was added in PHP 4.0.1
Note: Be aware, that the behaviour of require_once() and include_once() may not be what you expect on a non case sensitive operating system (such as Windows).
This behaviour changed in PHP 5 - the path is normalized first so that C:\PROGRA~1\A.php is realized the same as C:\Program Files\a.php and the file is required just once.
Example 16-11. require_once() is case insensitive on Windows
<?php
require_once("a.php"); // this will include a.php
require_once("A.php"); // this will include a.php again on Windows! (PHP 4 only)
?>
| Warning |
Windows versions of PHP prior to PHP 4.3.0 do not support accessing remote files via this function, even if allow_url_fopen is enabled. |
See also require(), include(), include_once(), get_required_files(), get_included_files(), readfile(), and virtual().
Another Useful functions:
zend-macro.zend-mod-required | zend-macro.zend-mod-required-ex | internals.pdo.prerequisites | function.require | function.require-once | function.get-required-files |
PHP is a widely-used general-purpose scripting language that is especially suited for Web development and can be embedded into HTML. If you are new to PHP and want to get some idea of how it works, try the introductory tutorial. After that, check out the online manual, and the example archive sites and some of the other resources available in the links section.