Loop until a key (i.e. enter or ESC) is pressed

Ruby
1

I’m very new to Ruby (3 days).

How do I escape from the loop below? - Without doing a CTRL-C.

loop forever…but I want to exit from it when a key is pressed

def loopy

i = 0

while true

i+=1

puts i

end

end

loopy

2

On Oct 30, 2007, at 8:43 AM, Wurzel Cidermaker wrote:

puts i

end
end
loopy

You will need to run your loopy method in a separate thread, and then
kill that thread when the user presses any key on the keyboard …

t = Thread.new do
i = 0
while true
i += 1
puts i
end
end

gets
t.kill

The above code won’t work with any keypress – you have to hit enter
in order to stop the program.

Blessings,
TwP

3

Tim P. wrote:

You will need to run your loopy method in a separate thread, and then
kill that thread when the user presses any key on the keyboard …

t = Thread.new do
i = 0
while true
i += 1
puts i
end
end

gets
t.kill

The above code won’t work with any keypress – you have to hit enter
in order to stop the program.

Blessings,
TwP

That does work properly.

Is starts to display

1
2
3
…
…
127

then stops and I presume is waiting for the “gets”

To put this into some context;

I have a socket client program that continously reads data from a
server, the only way I have currently to stop it is to do a CTRL-C, I
want/would expect a more elegant way of performing an exit on a loop.

4

ara.t.howard wrote:

On Oct 30, 2007, at 9:50 AM, Wurzel Cidermaker wrote:

then stops and I presume is waiting for the “gets”

To put this into some context;

I have a socket client program that continously reads data from a
server, the only way I have currently to stop it is to do a CTRL-C, I
want/would expect a more elegant way of performing an exit on a loop.

start this before you fire up your socket stuff

reaper =
Thread.new do
loop do
Kernel.exit if gets == ‘exit’
end
end

if you type exit, your program will exit. check out highline or
search the archives if you want something more elegant - exiting a
loop and accepting cross platform user input is a real can of worms
made complex by the lack of getch() on *nix platforms, the
idiosyncracies of termninal attributes, and buffering issues with pty
vs not.

regards

a @ http://codeforpeople.com/

thanks for your response but I struggling to implement it.

can you please fix what I have below?

example

def loopy

loop do

puts Time.now
sleep 1

end

end

reaper =
Thread.new do
loop do
Kernel.exit if gets == ‘exit’
end
end

loopy

5

On Oct 30, 2007, at 9:50 AM, Wurzel Cidermaker wrote:

then stops and I presume is waiting for the “gets”

To put this into some context;

I have a socket client program that continously reads data from a
server, the only way I have currently to stop it is to do a CTRL-C, I
want/would expect a more elegant way of performing an exit on a loop.

start this before you fire up your socket stuff

reaper =
Thread.new do
loop do
Kernel.exit if gets == ‘exit’
end
end

if you type exit, your program will exit. check out highline or
search the archives if you want something more elegant - exiting a
loop and accepting cross platform user input is a real can of worms
made complex by the lack of getch() on *nix platforms, the
idiosyncracies of termninal attributes, and buffering issues with pty
vs not.

regards

a @ http://codeforpeople.com/

6

thanks…but…

doesn’t work on my Windows XP box!

it prints the time once, then waits for input.

any ideas why?

7

On Oct 30, 2007, at 10:38 AM, Wurzel Cidermaker wrote:

end

reaper =
Thread.new do
loop do
Kernel.exit if gets == ‘exit’
end
end

loopy

sorry, my fault, that ‘gets’ will have a newline on it, this works:

cfp:~ > ruby a.rb
Tue Oct 30 11:01:32 -0600 2007
Tue Oct 30 11:01:33 -0600 2007
Tue Oct 30 11:01:34 -0600 2007
Tue Oct 30 11:01:35 -0600 2007
Tue Oct 30 11:01:36 -0600 2007
exit

cfp:~ > cat a.rb
def loopy
loop do
puts Time.now
sleep 1
end
end

reaper =
Thread.new do
loop do
Kernel.exit if gets =~ /exit/
end
end

loopy

regards.

a @ http://codeforpeople.com/

8

On Oct 30, 2007, at 11:17 AM, Wurzel Cidermaker wrote:

thanks…but…

doesn’t work on my Windows XP box!

it prints the time once, then waits for input.

any ideas why?

you can’t easily multi-plex io on windows with ruby. search the
archvies but, mostly, this is very slippery and you have to have a
deep understanding of ruby’s thread model to accomplish it. search
for ‘threads blocking windows’ in the archives. on *nix it’s quite
easy - with windows you are going to have to adapt to a multi process
model i think. it’s hard to say without knowing the details of your
program.

sorry!

a @ http://codeforpeople.com/

9

Another possible approach is to use trap to catch the TERM or INT
signals. From there, you can use a variety of strategies to shut the
program down gracefully. You can either hit CTRL-C (or CTRL-D if you
catch TERM) or write a very simple second program that sends the
signal to the first program (start and stop scripts, basically). The
second program will need the process id for the first, which could be
written out to a designated file using $$.

I don’t know if trap is supported on Vista. One method of implementing
trap on Windows I’ve seen (but never used personally) is to wrap the
Kernel’s trap method, like this:

def trap(signal)
Kernel::trap(signal){yield}
Thread.new{loop{sleep 1}}
end

You can easily simulate a trap by simply checking a designated file
(you can use $$ to generate a unique filename) for a termination
string (like TERM, ASCII 4) on each iteration of the loop. Then your
shutdown script would simply write the termination string to the file
and exit. The listener script would see the exit string and shut down.

As noted by Ara, this problem is much simpler on Unix, where threading
is better supported. In the next version of Ruby, native threading
will be supported (including on Vista) so hopefully you won’t need
these kinds of tricks.

Dan

Dan Y.
http://dev.zeraweb.com/
Ruby And JavaScript Consulting