Jazz Up Your CLI with Progress Tracking

I have a BeanShell script that takes a few minutes to run. I wanted to provide some feedback on the progress to the user.

The JUnit text UI tracks progress by printing a series of dots, one per test. This works fine for a relatively small and fixed number of items like unit tests, but in my case, the number of items is much larger and variable. When I tried this approach with my script, the dots scrolled off of the screen, and as a user, I really had no idea how many dots to expect.

  $ java junit.textui.TestRunner 
  .........................................
  .........................................
  ............................
  Time: 2.609

  OK (110 tests)

I decided I wanted to print out the percentage of completion in place; the current percentage should overwrite the previous value. I accomplished this using the backspace character '\b':

  print(s) {
    System.out.print(s);
  }

  /**
   * Print percentage, where "percent" is between 0 and 100.
   */
  printPercent(int percent) {
    // clear previous value.
    print("\b\b\b\b");

    if (percent < 10)
      print(" ");
    if (percent < 100)
      print(" ");
    print(percent);
    print("%");
  }

If I want to get fancy, I can further enhance the script and print out an estimated time to completion. One caveat, special characters play nicely with terminals, but not so when you redirect output to a file.