How to detect Return or Enter key properly when using Curses

Question

I am wanting to learn Ruby so I thought I'd try and learn it and Curses at the same time. I am creating a navigation menu that allows the user to select options which will run system commands.

I have gotten to the point where my navigation menu is created and I can cycle through options using the arrow keys.

Now I am trying to read the Enter key as input and run a system command when Enter is pressed. Example:

    input = menu.getch
    if input == ENTER

in

  position = 3 if position < 0
  position = 0 if position > 3
  draw_menu(menu, position)
  if position == 0
    draw_info menu, 'You selected option 0'
    input = menu.getch
    if input == ENTER
      menu.clear
      menu.refresh
      puts (system 'ls')

    end

When the Enter key is pressed, the system command does work(kind of) but I am having a problem where the system command is also run if the option is just selected or highlighted. I only want it to work if the Enter key is pressed.

If I change it to

    if input == 'k'

The system command only runs when the Enter key is pressed. It will not run when highlighted or selected. This is the way I want it to work.

Any ideas on how I can get the Enter key to function the same as the 'k' key?

Here is my code.

require 'curses'
include Curses

# Top Lie
SCREEN_WIDTH       = 90
HEADER_HEIGHT      = 4
HEADER_WIDTH       = SCREEN_WIDTH

# Bottom Line
SCREEN_WIDTH2      = 90
HEADER_HEIGHT2      = 1
HEADER_WIDTH2       = SCREEN_WIDTH2

Curses.init_screen
Curses.curs_set(0)  # Invisible cursor

Curses.start_color

Curses.noecho # echo or noecho to display user input
Curses.nonl
Curses.raw
Curses.stdscr.nodelay = 1

Curses.init_pair(1, Curses::COLOR_WHITE, Curses::COLOR_BLUE)
Curses.init_pair(2, Curses::COLOR_WHITE, Curses::COLOR_BLUE)

begin

  # Top Line
  header_window = Curses::Window.new(HEADER_HEIGHT, HEADER_WIDTH, 0, 0)   # (height, width, top, left)
  header_window.color_set(1)
  header_window << "Curses example".center(HEADER_WIDTH)
  header_window.refresh

  # Bottom Line
  header2_window = Curses::Window.new(HEADER_HEIGHT, HEADER_WIDTH, 23, 0)
  header2_window.color_set(2)
  header2_window << "Curses example".center(HEADER_WIDTH)
  header2_window.refresh

  # Building a static window

    def draw_menu(menu, active_index=nil)
      ["This is option 0.", "This is option 1.", "This is option 2.", "This is option 3."].each_with_index do |element, index|
      # "w" for word array
      # It's a shortcut for arrays
        menu.setpos(index + 1, 1)
        menu.attrset(index == active_index ? A_STANDOUT : A_NORMAL)
        menu.addstr("#{index} - %-10s" % element)   # %-Xs makes sure array words line up evenly if you place index after element
                                                    # you can change 17 to another number
      end
      menu.setpos(5, 1)
    end

    def draw_info(menu, text)
      menu.setpos(6, 1)  # sets the position of move up and down
                         # for example, menu.setpos(1, 10) moves to another
                         # location
      menu.attrset(A_NORMAL)
      menu.addstr text
    end

    position = 0

    menu = Window.new(20, 70, 2, 2)  # (height, width, top, left)
    menu.keypad = true  # enable keypad which allows arrow keys
    #menu.box('|', '-')
    draw_menu(menu, position)
    while ch = menu.getch
      stdscr.keypad = true
      case ch
      when KEY_UP, 'w'
        #draw_info menu, 'move up'
        position -= 1
      when KEY_DOWN, 's'
        #draw_info menu, 'move down'
        position += 1
      when 'x'
        exit
      end
      position = 3 if position < 0
      position = 0 if position > 3
      draw_menu(menu, position)
      if position == 0
        draw_info menu, 'You selected option 0'
        input = menu.getch
        if input == 'k'  # I want this to be ENTER
            menu.clear
            menu.refresh
            puts (system 'ls')  # This does not work well.  I need to fix it.

        end
      elsif position == 1
        draw_info menu, 'You selected option 1'
      elsif position == 2
        draw_info menu, 'You selected option 2'
      else position == 3
        draw_info menu, 'You selected option 3'
      end       
    end

rescue => ex
  Curses.close_screen
end

score 1 · Answer 1 · answered Aug 06 '17 at 20:34

There may be additional problems, but the one you're likely running into is that the Enter key on your keyboard usually is not what curses (ncurses) calls KEY_ENTER. Instead, that's usually assigned to the Enter on the numeric keypad (and it sends an escape sequence when keypad mode is enabled). That's discussed in proper way of catching control+key in ncurses.

Also, your initialization using

Curses.raw

prevents curses from returning KEY_ENTER in any case. That is, curses wouldn't recognize the escape sequence assigned to that code. You might want to try

Curses.cbreak
Curses.stdscr.keypad = 1

which (unless something not shown is making KEY_UP and KEY_DOWN work) will help with the other KEY_xxx symbols, and where you're expecting "ENTER", to accept a newline \n character. That's more likely to do what you expect.

How to detect Return or Enter key properly when using Curses

1 Answers1

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