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Simulate `bash` behaviour using Python and named pipes.

+1 vote
521 views

I am trying to understand how to use named pipes in python to launch external processes (in a Linux environment).

As an example I am trying to "imitate" the behaviour of the following sets of commands is bash:

> mkfifo named_pipe
> ls -lah > named_pipe &
> cat < named_pipe

In Python I have tried the following commands:

import os
import subprocess as sp

os.mkfifo("named_pipe",0777) #equivalent to mkfifo in bash..
fw = open("named_pipe",'w')
#at this point the system hangs...

My idea it was to use subprocess.Popen and redirect stdout to fw... next open named_pipe for reading and giving it as input to cat (still using Popen).

I know it is a simple (and rather stupid) example, but I can't manage to make it work..

How would you implement such simple scenario?

posted Aug 5, 2013 by Sonu Jindal

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1 Answer

+1 vote

You can pipe using subprocess
p1 = subprocess.Popen(["ls", "-lah"], stdout=subprocess.PIPE) p2 = subprocess.Popen(["cat"], stdin=p1.stdout)p1.wait()p2.wait()

You can also pass a file object to p1s stdout and p2s stdin if you want to pipe via a file. with open("named_pipe", "rw") as named_pipe:
p1 = subprocess.Popen(["ls", "-lah"], stdout=named_pipe) p2 = subprocess.Popen(["cat"], stdin=named_pipe) p1.wait() p2.wait() Luca

answer Aug 5, 2013 by Luv Kumar
I am aware of the first solutions, just now I would like to experiment a bit with using named pipes (I also know that the example is trivial, but it just to grasp the main concepts)

Your second example doesn't work for me.. if named_file is not a file in the folder I get an error saying that there is not such a file.

If I create named_pipe as a named pipe using os.mkfifo("named_file",0777) than the code hangs.. I think it is because there is not process that reads the content of the pipe, so the system waits for the pipe to be emptied.
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