/**
  * Удаляет сегменты с точками из пути.
  *
  * Алгоритм описан по ссылке:
  * https://tools.ietf.org/html/rfc3986#section-5.2.4
  *
  */
function removeDotSegments($path) {
  $input = $path;
  $out = array();
  while (strlen($input)) {
    // A.  If the input buffer begins with a prefix of "../" or "./",
    //     then remove that prefix from the input buffer; otherwise,
    $input = preg_replace('#^[.][.]?/#', '/', $input);
    // B.  if the input buffer begins with a prefix of "/./" or "/.",
    //     where "." is a complete path segment, then replace that
    //     prefix with "/" in the input buffer; otherwise,
    if (substr($input, 0, 3) === '/./') {
      $out[] = '/';
      $input = substr($input, 2);
      continue;
    }
    if ($input == '/.') {
      $out[] = '/';
      break;
    }
    // C.  if the input buffer begins with a prefix of "/../" or "/..",
    //     where ".." is a complete path segment, then replace that
    //     prefix with "/" in the input buffer and remove the last
    //     segment and its preceding "/" (if any) from the output
    //     buffer; otherwise,
    if (substr($input, 0, 4) === '/../') {
      array_pop($out);
      $input = substr($input, 3);
      continue;
    }
    if ($input === '/..') {
      $out[] = '/';
      break;
    }
    // D.  if the input buffer consists only of "." or "..", then remove
    //     that from the input buffer; otherwise,
    if ($input === '.' || $input === '..') {
      break;
    }
    // E.  move the first path segment in the input buffer to the end of
    //     the output buffer, including the initial "/" character (if
    //     any) and any subsequent characters up to, but not including,
    //     the next "/" character or the end of the input buffer.
    $pos = strpos($input, '/', 1);
    if ($pos === false) {
      $out[] = $input;
      break;
    }
    $out[] = substr($input, 0, $pos);
    $input = substr($input, $pos);
  }
  return implode($out);
}


// STEP   OUTPUT BUFFER         INPUT BUFFER
//
//       1 :                         /a/b/c/./../../g
//       2E:   /a                    /b/c/./../../g
//       2E:   /a/b                  /c/./../../g
//       2E:   /a/b/c                /./../../g
//       2B:   /a/b/c                /../../g
//       2C:   /a/b                  /../g
//       2C:   /a                    /g
//       2E:   /a/g
var_dump(removeDotSegments('/a/b/c/./../../g'));