code: public function binaryVersion()
      {
          if (!self::$version) {
              if (0 === $this->process->execute('svn --version', $output)) {
                  if (preg_match('{(\d+(?:\.\d+)+)}', $output, $match)) {
                      self::$version = $match[1];
                  }
              }
          }
  
          return self::$version;
      }
docs: Returns the version of the svn binary contained in PATH
  
  @return string|null