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

ruby-talk
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

···

--
Posted via http://www.ruby-forum.com/.

2

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

···

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

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

3

Tim Pease 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.

···

--
Posted via http://www.ruby-forum.com/\.

4

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/

···

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.

--
it is not enough to be compassionate. you must act.
h.h. the 14th dalai lama

5

ara.t.howard 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

···

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

--
Posted via http://www.ruby-forum.com/\.

6

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/

···

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

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

--
it is not enough to be compassionate. you must act.
h.h. the 14th dalai lama

7

thanks...but...

doesn't work on my Windows XP box!

it prints the time once, then waits for input.

any ideas why?

···

--
Posted via http://www.ruby-forum.com/.

8

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/

···

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?

--
it is not enough to be compassionate. you must act.
h.h. the 14th dalai lama

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 Yoder
http://dev.zeraweb.com/
Ruby And JavaScript Consulting

On Oct 30, 11:41 am, "ara.t.howard" <ara.t.how...@gmail.com> wrote:

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/
--
it is not enough to be compassionate. you must act.
h.h. the 14th dalai lama