Persistent Command Line Display

Question

I am writing a little Sudoku solving app in Ruby that just outputs to the terminal. For example:

 ruboku $ ruby grid.rb
+---+---+---+---+---+---+---+---+---+
| 2 | 8 | 5 |   | 3 | 1 | 7 | 6 | 9 |
+---+---+---+---+---+---+---+---+---+
| 5 |   | 4 | 8 | 7 | 2 | 1 | 9 | 3 |
+---+---+---+---+---+---+---+---+---+
|   |   |   |   |   |   |   |   |   |
+---+---+---+---+---+---+---+---+---+
|   |   |   |   |   |   |   |   |   |
+---+---+---+---+---+---+---+---+---+
|   |   |   |   |   |   |   |   |   |
+---+---+---+---+---+---+---+---+---+
|   |   |   |   |   |   |   |   |   |
+---+---+---+---+---+---+---+---+---+
|   |   |   |   |   |   |   |   |   |
+---+---+---+---+---+---+---+---+---+
|   |   |   |   |   |   |   |   |   |
+---+---+---+---+---+---+---+---+---+
|   |   |   |   |   |   |   |   |   |
+---+---+---+---+---+---+---+---+---+

Is there a way to keep this as a persistent display such that when there is new information to show it doesn't print a new line, but updates the grid that is already displaying?

I've seen some tools such as ngrok who do this.

Thanks for your time,

Tom

Answer 1

Depending on your needs, erasing the screen and creating the grid again could be good enough :

def show_grid
  line = '+---+---+---+---+---+---+---+---+---+'
  puts line
  9.times do
    row = (1..9).map { rand(9) + 1 }
    puts '| ' + row.join(' | ') + ' |'
    puts line
  end
end

def clear_screen
  system('clear') || system('cls')
end

loop do
  clear_screen
  show_grid
  sleep 1
end

It outputs

+---+---+---+---+---+---+---+---+---+
| 1 | 2 | 7 | 3 | 4 | 9 | 8 | 6 | 5 |
+---+---+---+---+---+---+---+---+---+
| 1 | 8 | 1 | 7 | 6 | 2 | 2 | 1 | 3 |
+---+---+---+---+---+---+---+---+---+
| 2 | 2 | 1 | 2 | 2 | 8 | 2 | 3 | 6 |
+---+---+---+---+---+---+---+---+---+
| 5 | 3 | 6 | 1 | 5 | 3 | 2 | 7 | 9 |
+---+---+---+---+---+---+---+---+---+
| 9 | 7 | 7 | 4 | 7 | 2 | 2 | 9 | 1 |
+---+---+---+---+---+---+---+---+---+
| 5 | 9 | 1 | 9 | 3 | 7 | 8 | 3 | 1 |
+---+---+---+---+---+---+---+---+---+
| 8 | 5 | 4 | 7 | 3 | 2 | 2 | 5 | 3 |
+---+---+---+---+---+---+---+---+---+
| 4 | 7 | 1 | 1 | 4 | 8 | 4 | 1 | 1 |
+---+---+---+---+---+---+---+---+---+
| 1 | 1 | 8 | 4 | 2 | 4 | 8 | 3 | 8 |
+---+---+---+---+---+---+---+---+---+

then

+---+---+---+---+---+---+---+---+---+
| 6 | 4 | 4 | 3 | 5 | 5 | 8 | 9 | 1 |
+---+---+---+---+---+---+---+---+---+
| 7 | 7 | 7 | 3 | 3 | 2 | 8 | 7 | 6 |
+---+---+---+---+---+---+---+---+---+
| 6 | 2 | 2 | 1 | 4 | 7 | 1 | 1 | 9 |
+---+---+---+---+---+---+---+---+---+
| 3 | 8 | 7 | 7 | 7 | 9 | 7 | 4 | 4 |
+---+---+---+---+---+---+---+---+---+
| 4 | 1 | 2 | 8 | 6 | 7 | 1 | 9 | 3 |
+---+---+---+---+---+---+---+---+---+
| 6 | 7 | 7 | 5 | 1 | 7 | 6 | 7 | 4 |
+---+---+---+---+---+---+---+---+---+
| 8 | 2 | 3 | 5 | 3 | 5 | 4 | 7 | 2 |
+---+---+---+---+---+---+---+---+---+
| 5 | 9 | 3 | 2 | 4 | 2 | 9 | 6 | 3 |
+---+---+---+---+---+---+---+---+---+
| 1 | 7 | 8 | 9 | 4 | 3 | 4 | 1 | 5 |
+---+---+---+---+---+---+---+---+---+

then...

It should work on Windows/Linux/MacOs.

For anything more complex, you'll need an ncurses gem.

Answer 2

So the question is marked as answered I thought I would write up the advice given to me in the comments.

It looks like the ncurses ruby gem and vedeu offer the functionality that I need. Another alternative would be to clear the scren and reprint the output.