[Shell] "looping" i/o redirection

probabil1ty · 12-27-2006, 06:42 PM

Hi !

I would like to test a connect five program by making it playing against another version of the same program.
The program takes the opponent's move via standard input and output its move via standard output.
The idea would be to redirect prog1's output to prog2's input and then redirect prog2's output to prog1's input and so on, until one of the two program exits.

How can I do that ?

penguiniator · 12-27-2006, 06:52 PM

You can do that with named pipes. Here is a tutorial explaining how to do it in the shell.

http://www2.linuxjournal.com/article/2156

probabil1ty · 12-27-2006, 07:06 PM

Quote:

You can do that with named pipes. Here is a tutorial explaining how to do it in the shell.

http://www2.linuxjournal.com/article/2156

Seems to be what I need.
Thanks for helping a newbie like me and sorry for wasting your time ;-)

probabil1ty · 12-28-2006, 10:09 AM

Take this script:

Code:

#!/bin/bash
read
echo "first reply: "$REPLY""
read
echo "second reply: "$REPLY""
exit 0

If I try to use a pipe with this script, it does not read the second input.
For example, running

Code:

echo "hello world" | ./test

would output:

Quote:

first reply: hello world
second reply:

How can I make the program wait for the second input as well ?

makyo · 12-28-2006, 10:33 AM

Hi.

What second input?

I used:
echo "one\ntwo"
and it seemed to work:

Code:

% echo "one\ntwo" | ./s1
first reply: one
second reply: two

Does this not work for you?

Best wishes ... cheers, makyo

probabil1ty · 12-28-2006, 02:21 PM

Quote:

I used:
echo "one\ntwo"
and it seemed to work:
Code:

% echo "one\ntwo" | ./s1 first reply: one second reply: two

Does this not work for you?

It works (using echo -e), but I need the program to take only the first input and wait for the second. It would give something like that:

Code:

% echo "onetwo" | ./test
first reply: onetwo

(then the program waits for another input)

How can I do that ?

Thanks for your help.

makyo · 12-28-2006, 03:55 PM

Hi.

It did wait for another input. You told it to read from the pipe and not from the keyboard. It read the line that you echoed in, and displayed it. Then it read from the pipe again, and got an EOF.

Perhaps we should clarify: from where did you expect the second input to come? ... cheers, makyo

probabil1ty · 12-28-2006, 04:14 PM

Quote:

from where did you expect the second input to come?

In that precise test, I would like the second input to come from the keyboard, but the first to come from the pipe.
But I would like to be able to do this:

Quote:

to redirect prog1's output to prog2's input and then redirect prog2's output to prog1's input and so on, until one of the two program exits.

I am not sure exactly how to do that, since in my test the script seems to take all its input via only one pipe, whereas I would like the program to take it from different sources (I think via a second named pipe).

probabil1ty · 12-29-2006, 06:37 PM

No idea ? I think it should be quite simple, but I am just a poor newbie with very basic knowledge of the shell...

Basically I would like to find a way to get a program's input from different sources (pipes).

spirit receiver · 12-30-2006, 08:51 AM

Have a look at this:

Code:

ada@barnabas:~/tmp> cat test
#!/bin/bash
# This script is named "test"
while read
do
  echo "\"test\" received \"$REPLY\"." >&2
  sleep 2
  echo "ping"
done

ada@barnabas:~/tmp> cat test2
#!/bin/bash
# This script is named "test2"
while read
do
  echo "\"test2\" received \"$REPLY\"." >&2
  sleep 2
  echo "pong"
done

ada@barnabas:~/tmp> echo "ping" | ./test2
"test2" received "ping".
pong

ada@barnabas:~/tmp> mkfifo 1to2 2to1
ada@barnabas:~/tmp> ./test >1to2 <2to1 &
[3] 7678
ada@barnabas:~/tmp> ./test2 <1to2 >2to1 &
[4] 7683
ada@barnabas:~/tmp> echo "ping" > 1to2

ada@barnabas:~/tmp> "test2" received "ping".
"test" received "pong".
"test2" received "ping".
"test" received "pong".
"test2" received "ping".
"test" received "pong".
"test2" received "ping".
"test" received "pong".
"test2" received "ping".
"test" received "pong".
"test2" received "ping".
[...]

probabil1ty · 12-30-2006, 10:44 AM

Thanks a lot, everything is working well now.
I hadn't done enough testing myself actually, thanks again for your time.