(PHP 4, PHP 5, PHP 7)
opendir — Open directory handle
$path
   [, resource $context
  ] ) : resourceOpens up a directory handle to be used in subsequent closedir(), readdir(), and rewinddir() calls.
pathThe directory path that is to be opened
context
       For a description of the context parameter, 
       refer to the streams section of
       the manual.
      
   Returns a directory handle resource on success,
    or FALSE on failure
  
Upon failure, an E_WARNING is emitted.
   This may happen if path is not a valid directory,
   the directory can not be opened due to permission restrictions,
   or due to filesystem errors.
  
Example #1 opendir() example
<?php
$dir = "/etc/php5/";
// Open a known directory, and proceed to read its contents
if (is_dir($dir)) {
    if ($dh = opendir($dir)) {
        while (($file = readdir($dh)) !== false) {
            echo "filename: $file : filetype: " . filetype($dir . $file) . "\n";
        }
        closedir($dh);
    }
}
?>
The above example will output something similar to:
filename: . : filetype: dir filename: .. : filetype: dir filename: apache : filetype: dir filename: cgi : filetype: dir filename: cli : filetype: dir