Ruby STDIN.getc does not read char on reception

Question

Seems that Ruby IO#getc wait until receiving a \n before returning the chars.

If you try running this script:

STDOUT.sync = true
STDIN.sync = true
while data = STDIN.getc
  STDOUT.puts "Char arrived"
end

It will return one "Char arrived" per char sent to stdin, but only after a \n has been sent.

Seems that all char are buffered even if I write STDIN.sync = true.

Does anyone knows how to make the script print "Char arrived" right after a char has been sent to STDIN ?

Possible duplicate of [Get Single Char from Console Immediately](http://stackoverflow.com/questions/8072623/get-single-char-from-console-immediately) or [How to Get a Single Character in Ruby without Pressing Enter](http://stackoverflow.com/questions/174933/how-to-get-a-single-character-in-ruby-without-pressing-enter) (which have several good answers on how to solve this). — Phrogz, Nov 15 '11 at 21:03

WarHog · Accepted Answer · 2011-11-15T21:03:14.190

8

There was an answer from Matz :)

UPDATE

Also, you can use gem entitled highline, because using above example may be linked with strange screen effects:

require "highline/system_extensions"
include HighLine::SystemExtensions

while k = get_character
  print k.chr
end

edited Nov 15 '11 at 21:03

answered Nov 15 '11 at 20:57

WarHog

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+1 for citing a post from over 11.5 years ago. :) See the question I linked to for more answers that you can compile into yours. – Phrogz Nov 15 '11 at 21:03
Yeah, that post is ancient, but as you can see it's still actual :D – WarHog Nov 15 '11 at 21:06
Thanks for your quick answer. This makes my day. It explains some strange behaviour I had with other programs. – Martinos Nov 15 '11 at 21:13

score 2 · Answer 2 · edited May 23 '17 at 12:03

2

Adapted from from another answered question.

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

p get_char # => "q"

edited May 23 '17 at 12:03

Community

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1

answered Nov 15 '11 at 21:04

Sean Vikoren

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drewish · Answer 3 · 2019-07-25T15:59:10.060

0

https://stackoverflow.com/a/27021816/203673 and its comments are the best answer in the ruby 2+ world. This will block to read a single character and exit when ctrl + c is pressed:

require 'io/console'

STDIN.getch.tap { |char| exit(1) if char == "\u0003" }

edited Jul 25 '19 at 15:59

answered Jul 25 '19 at 15:48

drewish

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score 0 · Answer 4 · answered May 14 '20 at 17:15

From https://flylib.com/books/en/2.44.1/getting_input_one_character_at_a_time.html

def getch
  state = `stty -g`
  begin
    `stty raw -echo cbreak`
    $stdin.getc
  ensure
    `stty #{state}`
  end
end

while (k = getch)
  print k.chr.inspect
  sleep 0.2
end

Ruby STDIN.getc does not read char on reception

4 Answers4