normalize_path.php

<?php

$path_samples = array(
    '/temp/hoge/foo',
    '/temp/./hoge/foo',
    '/temp//hoge/foo',
    '/temp///hoge/foo',
    '/temp//bar/../hoge/foo',
    '/temp/bar/../../../..//temp//bar/../hoge/foo',
    '/temp/bar/../../../..//temp//bar/../hoge/foo////',
);

foreach ($path_samples as $path) {
    echo normalize_path($path);echo "\n";
}

function normalize_path($path) {
    $delimiter = DIRECTORY_SEPARATOR;
    $splited = explode($delimiter, $path);

    $realpath_stack = array();
    foreach ($splited as $name) {
        switch ($name) {
            case '..':
                array_pop($realpath_stack);
                continue;
            case '.':
            case '':
                continue;
            default:
                $realpath_stack[] = $name;
        }
    }

    return $delimiter.implode($delimiter, $realpath_stack);
}