(PHP 4, PHP 5, PHP 7)
chdir — Change directory
$directory
   ) : bool
   Changes PHP's current directory to 
   directory.
  
directoryThe new current directory
   Returns TRUE on success or FALSE on failure.
  
   Throws an error of level E_WARNING on failure.
  
Example #1 chdir() example
<?php
// current directory
echo getcwd() . "\n";
chdir('public_html');
// current directory
echo getcwd() . "\n";
?>
The above example will output something similar to:
/home/vincent /home/vincent/public_html
Note: When safe mode is enabled, PHP checks whether the directory in which the script is operating has the same UID (owner) as the script that is being executed.
    If the PHP interpreter has been built with ZTS (Zend Thread Safety) enabled,
    any changes to the current directory made through chdir()
    will be invisible to the operating system. All built-in PHP functions will
    still respect the change in current directory; but external library
    functions called using FFI will not. You
    can tell whether your copy of PHP was built with ZTS enabled using
    php -i or the built-in constant
    PHP_ZTS.