46

How can I get a single keyboard character from the terminal with Ruby without pressing enter? I tried Curses::getch, but that didn't really work for me.

the Tin Man
  • 158,662
  • 42
  • 215
  • 303
Nino
  • 5,261
  • 4
  • 22
  • 15
  • 2
    possible duplicate of [Get single char from console immediately](http://stackoverflow.com/questions/8072623/get-single-char-from-console-immediately) – Phrogz Nov 15 '11 at 21:05

6 Answers6

72

Since ruby 2.0.0, there is a 'io/console' in the stdlib with this feature

require 'io/console'
STDIN.getch
iNecas
  • 1,743
  • 1
  • 13
  • 16
37

http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/2999

#!/usr/bin/ruby

begin
  system("stty raw -echo")
  str = STDIN.getc
ensure
  system("stty -raw echo")
end
p str.chr

(Tested on my OS X system, may not be portable to all Ruby platforms). See http://www.rubyquiz.com/quiz5.html for some additional suggestions, including for Windows.

Jay
  • 41,768
  • 14
  • 66
  • 83
  • That works so far, but unfortunately i get a numeric and not a string. du you know how to convert the numeric to the right ascii-character? – Nino Oct 06 '08 at 16:33
  • 2
    Yes, just use str.chr to get the character corresponding to the numeric value. I've updated the post to reflect that – Jay Oct 06 '08 at 16:50
  • 1
    Unfortunately since you're in raw mode, control-C gets sent in as a character, not as a SIGINT. So if you want blocking input like above, but still want to let the user hit control-C to stop the program while it's waiting, make sure to do this: `Signal.trap("INT") { exit }` (see my answer below for a better formatted version) – AlexChaffee Nov 25 '11 at 21:10
  • 2
    The answer below by Andrew (on Jan 25 '13 at 17:49) is better. – Will Nov 03 '14 at 21:35
21

@Jay gave a great answer, but there are two problems:

  1. You can mess up default tty state;
  2. You ignore control characters (^C for SIGINT, etc).

A simple fix for that is to save previous tty state and use following parameters:

  • -icanon - disable canonical input (ERASE and KILL processing);
  • isig - enable the checking of characters against the special control characters INTR, QUIT, and SUSP.

In the end you would have a function like this:

def get_char
  state = `stty -g`
  `stty raw -echo -icanon isig`

  STDIN.getc.chr
ensure
  `stty #{state}`
end
Ian
  • 11,280
  • 3
  • 36
  • 58
Andrew
  • 8,330
  • 11
  • 45
  • 78
15

Raw mode (stty raw -echo) unfortunately causes control-C to get sent in as a character, not as a SIGINT. So if you want blocking input like above, but allow the user to hit control-C to stop the program while it's waiting, make sure to do this:

Signal.trap("INT") do # SIGINT = control-C
  exit
end

And if you want non-blocking input -- that is, periodically check if the user has pressed a key, but in the meantime, go do other stuff -- then you can do this:

require 'io/wait'

def char_if_pressed
  begin
    system("stty raw -echo") # turn raw input on
    c = nil
    if $stdin.ready?
      c = $stdin.getc
    end
    c.chr if c
  ensure
    system "stty -raw echo" # turn raw input off
  end
end

while true
  c = char_if_pressed
  puts "[#{c}]" if c
  sleep 1
  puts "tick"
end

Note that you don't need a special SIGINT handler for the non-blocking version since the tty is only in raw mode for a brief moment.

AlexChaffee
  • 8,092
  • 2
  • 49
  • 55
  • This answer is great, and exactly what I was looking for. Thanks so much for exceptionally functional code! – eddieroger Nov 29 '12 at 19:29
  • 1
    `Signal.trap('INT') { exit }` makes the program exit when control-C is pressed (unless it's bypassed by other means) and definitely works in 1.9.2-p290, so I don't know what "did not work for me" could mean – AlexChaffee Jan 19 '13 at 22:23
  • This works in your example, but it definitely does not work if you're using `STDIN.getch`. Then your SIGINT gets interpreted as `"\u0003"`. Or maybe something else depending on your terminal. – Justin Force Nov 18 '15 at 01:11
13

Note: This is and old answer and the solution no longer works on most systems.

But the answer could still be useful for some environments, where the other methods don't work. Please read the comments below.

First you have to install highline:

gem install highline

Then try if the highline method works for you:

require "highline/system_extensions"
include HighLine::SystemExtensions

print "Press any key:"
k = get_character
puts k.chr
Community
  • 1
  • 1
mit
  • 11,083
  • 11
  • 50
  • 74
  • 5
    Warning: a recent commit removed this feature from highline. See https://github.com/JEG2/highline/issues/50 – AlexChaffee Jan 25 '13 at 18:53
  • 2
    this does NOT work: it requires that you hit the key. Incidently, it also takes in the \n character. – erapert May 08 '13 at 22:16
  • This [example](https://github.com/JEG2/highline/blob/master/examples/get_character.rb) works for me on Ruby 2.0 on Windows 7. – zhon Dec 18 '13 at 19:18
  • Works on Ruby 1.9.3 and Windows XP without need to press enter (tested on pry). ps Thanks! – Darek Nędza Jan 30 '14 at 18:37
0

And if you are building curses application, you need to call 

nocbreak

http://www.ruby-doc.org/stdlib-1.9.3/libdoc/curses/rdoc/Curses.html#method-c-cbreak

lzap
  • 16,417
  • 12
  • 71
  • 108