include_path string Specifies a list of directories where the require, include, fopen(), file(), readfile() and file_get_contents() functions look for files. The format is like the system’s PATH environment variable: a list of directories separated with a colon in Unix or semicolon in Windows.
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set_include_path(get_include_path() . PATH_SEPARATOR . '/path/to/lib/'); //x.php belong here
//use of
require_once 'x.php';
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