realpath関数の使い方

realpath
(PHP 4, PHP 5)
realpath — Returns canonicalized absolute pathname
Report a bug
 Description
string 
realpath ( 
string $path )
realpath() expands all symbolic links and resolves references to '/./', '/../' and extra '/' characters in the input path and return the canonicalized absolute pathname.
Report a bug
 Parameters
path
The path being checked.
Note:
Whilst a path must be supplied, the value can be blank or NULL In these cases, the value is interpreted as the current directory.
Report a bug
Return Values
Returns the canonicalized absolute pathname on success. The resulting path will have no symbolic link, '/./' or '/../' components.
realpath() returns FALSE on failure, e.g. if the file does not exist.
Note:
The running script must have executable permissions on all directories in the hierarchy, otherwiserealpath() will return FALSE.
Report a bug
 Changelog
Version
Description
5.3.0
Prior to this release, if only the last path component did not exist, realpath() would not fail on *BSD systems. realpath() now fails in this case.
5.0.0
Prior to this release, a blank or NULL path would cause realpath() to return the directory name of the script.
Report a bug
 Examples
Example #1 realpath() example chdir('/var/www/');
echo realpath('./../../etc/passwd');
?>
The above example will output:

/etc/passwd

Example #2 realpath() on Windows
On windows realpath() will change unix style paths to windows style. echo realpath('/windows/system32');
?>
The above example will output:

C:\WINDOWS\System32