   #PHP Manual Control Structures include include_once

                 PHP Manual
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require_once()

   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.

     Note: require_once() was added in PHP 4.0.1pl2

     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).

   Example 11-8. 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!
   ?>

   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().
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