public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        new AsyncTest().execute("https://yt-dl.org/downloads/latest/youtube-dl");

    }

    void exec(String cmd, String directory){
        Log.d("test-ytdl",cmd);
        try {
            Process process = Runtime.getRuntime().exec(cmd,null, new File(directory) );
            try (InputStreamReader inputStreamReader = new InputStreamReader(process.getInputStream())) {
                BufferedReader bufferedReader = new BufferedReader(inputStreamReader);
                for (String line = bufferedReader.readLine(); line != null; line = bufferedReader.readLine()) {
                    Log.d("test-ytdl","=> "+line);
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
            Log.d("test-ytdl", " Error : "+e.getMessage());
        }
    }

    void downloadFile(String url, String filename) {
        // need android.permission.INTERNET
        try {
            URL u = new URL(url);
            URLConnection conn = u.openConnection();
            int contentLength = conn.getContentLength();
            DataInputStream stream = new DataInputStream(u.openStream());
            byte[] buffer = new byte[contentLength];
            stream.readFully(buffer);
            stream.close();
            FileOutputStream fos = openFileOutput(filename, Context.MODE_PRIVATE);
            fos.write(buffer);
            fos.flush();
            fos.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    private class AsyncTest extends AsyncTask<String, Void, Void> {

        @Override
        protected Void doInBackground(String... args) {

            File file = getFileStreamPath("youtube_dl");

            if(!file.exists())
                downloadFile(args[0], "youtube_dl");

            file.setExecutable(true, true);

            Log.d("test-ytdl", "# Current folder : " + file.getParent());
            exec("chmod 777 youtube_dl", file.getParent());
            exec("stat youtube_dl", file.getParent());
            exec("whoami", file.getParent());
            exec("youtube_dl", file.getParent());

            return null;
        }
    }
}

01-09 20:33:49.434 9927-9971/fr.klemek.testyoutubedl D/test-ytdl: # Current folder : /data/user/0/fr.klemek.testyoutubedl/files
01-09 20:33:49.434 9927-9971/fr.klemek.testyoutubedl D/test-ytdl: chmod 777 youtube_dl
01-09 20:33:49.556 9927-9971/fr.klemek.testyoutubedl D/test-ytdl: stat youtube_dl
01-09 20:33:49.637 9927-9971/fr.klemek.testyoutubedl D/test-ytdl: =>   File: `youtube_dl'
01-09 20:33:49.637 9927-9971/fr.klemek.testyoutubedl D/test-ytdl: =>   Size: 1614357     Blocks: 3160    IO Blocks: 4096    regular file
01-09 20:33:49.637 9927-9971/fr.klemek.testyoutubedl D/test-ytdl: => Device: 1030fh/66319d   Inode: 148472   Links: 1
01-09 20:33:49.640 9927-9971/fr.klemek.testyoutubedl D/test-ytdl: => Access: (777/-rwxrwxrwx)   Uid: (10022/  u0_a22)   Gid: (10022/  u0_a22)
01-09 20:33:49.640 9927-9971/fr.klemek.testyoutubedl D/test-ytdl: => Access: 2018-01-09 20:33:49.420537211
01-09 20:33:49.640 9927-9971/fr.klemek.testyoutubedl D/test-ytdl: => Modify: 2018-01-09 20:33:49.420537211
01-09 20:33:49.640 9927-9971/fr.klemek.testyoutubedl D/test-ytdl: => Change: 2018-01-09 20:33:49.550537211
01-09 20:33:49.641 9927-9971/fr.klemek.testyoutubedl D/test-ytdl: whoami
01-09 20:33:49.708 9927-9971/fr.klemek.testyoutubedl D/test-ytdl: => u0_a22
01-09 20:33:49.708 9927-9971/fr.klemek.testyoutubedl D/test-ytdl: youtube_dl
01-09 20:33:49.715 9927-9971/fr.klemek.testyoutubedl D/test-ytdl:  Error : Cannot run program "youtube_dl" (in directory "/data/user/0/fr.klemek.testyoutubedl/files"): error=13, Permission denied