src/Composer/Util/Filesystem.php
public function normalizePath($path)
    {
        $parts = array();
        $path = strtr($path, '\\', '/');
        $prefix = '';
        $absolute = false;

        // extract a prefix being a protocol://, protocol:, protocol://drive: or simply drive:
        if (preg_match('{^( [0-9a-z]{2,}+: (?: // (?: [a-z]: )? )? | [a-z]: )}ix', $path, $match)) {
            $prefix = $match[1];
            $path = substr($path, strlen($prefix));
        }

        if (substr($path, 0, 1) === '/') {
            $absolute = true;
            $path = substr($path, 1);
        }

        $up = false;
        foreach (explode('/', $path) as $chunk) {
            if ('..' === $chunk && ($absolute || $up)) {
                array_pop($parts);
                $up = !(empty($parts) || '..' === end($parts));
            } elseif ('.' !== $chunk && '' !== $chunk) {
                $parts[] = $chunk;
                $up = '..' !== $chunk;
            }
        }

        return $prefix.($absolute ? '/' : '').implode('/', $parts);
    }
public function normalizePath($path)
    {
        $parts = array();
        $path = strtr($path, '\\', '/');
        $prefix = '';
        $absolute = false;

        // extract a prefix being a protocol://, protocol:, protocol://drive: or simply drive:
        if (preg_match('{^( [0-9a-z]{2,}+: (?: // (?: [a-z]: )? )? | [a-z]: )}ix', $path, $match)) {
            $prefix = $match[1];
            $path = substr($path, strlen($prefix));
        }

        if (substr($path, 0, 1) === '/') {
            $absolute = true;
            $path = substr($path, 1);
        }

        $up = false;
        foreach (explode('/', $path) as $chunk) {
            if ('..' === $chunk && ($absolute || $up)) {
                array_pop($parts);
                $up = !(empty($parts) || '..' === end($parts));
            } elseif ('.' !== $chunk && '' !== $chunk) {
                $parts[] = $chunk;
                $up = '..' !== $chunk;
            }
        }

        return $prefix.($absolute ? '/' : '').implode('/', $parts);
    }
Normalize a path. This replaces backslashes with slashes, removes ending
slash and collapses redundant separators and up-level references.

@param  string $path Path to the file or directory
@return string