Trapping ESC key

Ruby
1

I am a Ruby newbie and am trying to implement problem 1 mentioned here -
http://www.rubyrailways.com/implementing-15-exercises-for-learning-a-new-programming-language/

I am stuck and can’t find a simple and portable way to trap the ESC key.
Any
pointers, help is most appreciated. The code I have now is -

require ‘Win32API’
def getchar
char = Win32API.new(“crtdll”, “_getch”, [], ‘L’).call
if char == 27 # ESC key
exit
end
end

i = 0
loop do
print "#{i+=1}, "
getchar
end

Thanks.

2

I am stuck and can’t find a simple and portable way to trap the ESC key. Any
pointers, help is most appreciated.

Will this do it?

http://www.ruby-forum.com/topic/85036#156718

http://blog.grayproductions.net/articles/2006/10/01/i-just-want-one-character

Harry

–

http://www.kakueki.com/ruby/list.html
Japanese Ruby List Subjects in English

3

On 3/16/07, Harry [email protected] wrote:

http://blog.grayproductions.net/articles/2006/10/01/i-just-want-one-character

Harry

Harry, I have tried HighLine but that’s not what I want (or am I making
a
mistake here?). I am trying to solve the problem - ** “Display series of
numbers (1,2,3,4, 5….etc) in an infinite loop. The program should quit
if
someone hits a specific key (Say ESCAPE key).”

Somehow I want to keep checking in a thread (this should be
non-blocking)
for the ESC key press. Once ESC is pressed my program terminates. Right
now,
my thread code blocks till I press ESC key, as you can see here -

require ‘Win32API’
def getchar
char = Win32API.new(“crtdll”, “_getch”, [], ‘L’).call
if char == 27 # ESC key
exit
end
end

i = 0
loop do
print "#{i+=1}, "
getchar
end

What should I do? Thanks.

4

RubyCrazy schrieb:

require ‘Win32API’
getchar
end

What should I do? Thanks.

Change your operating system, or don’t use threads with blocking
keyboard I/O. It doesn’t work on Windows. For your code above (which
doesn’t use threads) you could call the Win32 function “_kbhit” before
calling “_getch”. In a thread you could do the same in a busy loop, but
don’t forget to sleep a little bit inside the loop.

Regards,
Pit

5

From: I G [mailto:[email protected]] :

I am stuck and can’t find a simple and portable way to trap

the ESC key. Any

pointers, help is most appreciated. The code I have now is -

require ‘Win32API’

def getchar

char = Win32API.new(“crtdll”, “_getch”, [], ‘L’).call

if char == 27 # ESC key

exit

end

end

i = 0

loop do

print "#{i+=1}, "

getchar

end

can you try this sample?

C:\family\ruby\key_press>cat -n a1d.rb
1 #------------------------------
2 require ‘Win32API’
3
4 @@kbhit = Win32API.new(“msvcrt”, “_kbhit”, [], ‘I’)
5 @@getch = Win32API.new(“msvcrt”, “_getch”, [], ‘I’)
6
7 def capture_key
8 unless @@kbhit.call.zero?
9 yield @@getch.call
10 end
11 end
12
13 KEY_Esc = 27
14 $stdout.sync=true
15
16 i=0
17 loop do
18 capture_key do |key|
19 puts “keypressed: value #{key}, char #{key.chr}” if $DEBUG
20 if key == KEY_Esc
21 puts “Escaping key pressed. Exiting…” if $DEBUG
22 exit
23 end
24 end
25 sleep 1 #delay it since it’s too fast :slight_smile:
26 puts “#{i+=1}”
27 end
28 #------------------------------

C:\family\ruby\key_press>ruby -d a1d.rb
1
2
3
4
keypressed: value 117, char u
5
keypressed: value 101, char e
6
7
8
keypressed: value 119, char w
9
10
keypressed: value 120, char x
11
12
keypressed: value 27, char ?
Escaping key pressed. Exiting…

C:\family\ruby\key_press>

Hth.
kind regards -botp