Subprocess - then read - then write to same shell?

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November 26th, 2012, 08:03 AM

thetester

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Subprocess - then read - then write to same shell?

Please can someone explain how to do this:

I want to make some commands in a shell - read the output and based on the output make another input in the same shell

Code:

import subprocess
p = subprocess.Popen('some_program', stdin = subprocess.PIPE, stdout = subprocess.PIPE)
out, err = p.communicate()

if "abcdefg" in out:
    p.communicate(input = ' -c -d 1234')
    out, err = p.communicate()
    if "xyz" in out:
        print "I have been able to open a shell, read the output and give another command to the same shell"

I have looked at readlines, stdin.write etc but I am lost as to what the solution will be. It seems that as soon as I 'read' the output the process is then closed preventing me from giving any further inputs. If I open a new shell then its no good - because the 2nd commands must come after the 1st (if it meets a condition).

November 26th, 2012, 10:14 AM

b49P23TIvg

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Others and I solve this problem by searching the subprocess output for a known prompt. At that point we know the shell is ready for new input.

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November 26th, 2012, 10:57 AM

thetester

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Quote:

Originally Posted by b49P23TIvg

Others and I solve this problem by searching the subprocess output for a known prompt. At that point we know the shell is ready for new input.

But how do you do that? Once you have read the output it appears to then close it - so that you can't write anything else. What command do you use to search and what are you searching in?

November 26th, 2012, 11:20 AM

b49P23TIvg

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I can't help it if your program terminates. oh, yes, you could run it in a shell loop. Anyway, I helped some dude or dudette interact with a chess engine about a year ago. Click this underlined text. There are other examples, tell google to search with

Code:

site:forums.devshed.com/python-programming-11/ subprocess b49p23tivg

ha ha there are many hits.

November 27th, 2012, 07:06 AM

thetester

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Much appreciated for your quick and informative replies!

I have looked through but I'm still doubtful that subprocess can solve my problem - it seems once you search or read the output that the pipe is then closed.

I have however discovered the addon module 'pexpect'.

For example the following works:
Create two python files as below - the first must be called login.py (only because we call that specific file from the test.py main file - which is what we run). Test both cases by first entering correct password (password) and secondly entering an incorrect password ( =! password)

Code:

\\\\\\\\\login.py \\\\\\\\\
passw = raw_input('Enter PASS: ')
if passw == 'password':
    raw_input('You are logged in')
else:
    raw_input('Incorrect login')
\\\\\\\\\\\\\\\\\\\\\\\\\\\\\


/////// test.py /////////
import pexpect

child = pexpect.spawn('python login.py')
index = child.expect ('PASS')
if index==0:
    password = raw_input('Please enter your password: ')
    child.sendline (password)

index = child.expect (['logged in', 'Incorrect'])
if index ==0:
    print "Test output ===> you are logged in"
if index ==1:
    print "Test output ===> your password was incorrect"

raw_input('\nPress any key to quit')
\\\\\\\\\\\\\\\\\

I will experiment on my main set up to see if this will do its job in the project im working on.

November 27th, 2012, 02:52 PM

thetester

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Yes, the above works well when applied to my main project. This has helped me to reach a milestone today!

thanks for comments

Subprocess - then read - then write to same shell?

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