code: private static Optional<File> findExecutableOnSystemPath(final String executableName) {
      for (final String pathPath : Splitter.on(File.pathSeparator).split(System.getenv("PATH"))) {
        final File probeFile = new File(pathPath, executableName);
        if (probeFile.isFile() && java.nio.file.Files.isExecutable(probeFile.toPath())) {
          return Optional.of(probeFile);
        }
      }
      return Optional.absent();
    }
docs: warning: this will fail if the user has an escape path separator in a path