Subprocess module: running an interactive shell

Karthik Gurusamy kar1107 at gmail.com
Sun Mar 15 01:10:29 CET 2009


On Mar 14, 3:03 am, Roman Medina-Heigl Hernandez <ro... at rs-labs.com>
wrote:
> Karthik Gurusamy escribió:
>
>
>
> > On Mar 13, 6:39 pm, Roman Medina-Heigl Hernandez <ro... at rs-labs.com>
> > wrote:
> >> Hi,
>
> >> I'm experimenting with Python and I need a little help with this. What I'd
> >> like is to launch an interactive shell, having the chance to send first
> >> several commands from python. I've written the following code:
>
> >> =============
>
> >> #!/usr/bin/env python
>
> >> import sys, subprocess
>
> >> exe = "/bin/sh"
> >> params = "-i"
>
> > -i says shell to be interactive. So looks like it is directly trying
> > to read from the terminal.
>
> Well, then the question will be: is there any way to tell python to
> directly "map" the terminal to the subprocess?

pexpect seems to be the solution for such problems :). [other
applications include ssh which asks for password from terminal (not
ssh's stdin)]

http://pexpect.sourceforge.net/pexpect.html

>
> >> proc = subprocess.Popen([exe, params], stdin=subprocess.PIPE)
>
> > proc = subprocess.Popen([exe,], stdin=subprocess.PIPE)
>
> > works for me; but if there is an error 'sh' terminates.
>
> > If you want to simulate interactive, explore the pexpect module.
>
> I'll get it a try :)))
>
> >> proc.stdin.write("id\n")
>
> >> while True:
> >>         line = sys.stdin.readline()
> >>         if not line:
>
> > note that a simple enter terminates the shell which you may not want.
>
> Test my code and you'll see that this is not true :) When you hit enter
> line will contain '\n' so it's not empty.

You are right. I thought readline() strips the trailing \n (It doesn't
and shouldn't as it's necessary for the case a file ends without a
newline).

>
> >>                 break
> >>         proc.stdin.write(line)
>
> Btw, another curiosity I have: is it possible to make a print not
> automatically add \n (which is the normal case) neither " " (which happens
> when you add a "," to the print sentence)?  I found an alternative not
> using print at all, eg: sys.stdout.write("KKKKK"). But it resulted strange
> to me having to do that trick :)

I am also aware of only the sys.stdout.write solution.

python3.0 has a way to do it.

>>> help(print)
Help on built-in function print in module builtins:

print(...)
    print(value, ..., sep=' ', end='\n', file=sys.stdout)

    Prints the values to a stream, or to sys.stdout by default.
    Optional keyword arguments:
    file: a file-like object (stream); defaults to the current
sys.stdout.
    sep:  string inserted between values, default a space.
    end:  string appended after the last value, default a newline.

>>> print('hello', end='')
hello>>>

Karthik

>
> Thank you for all your comments and comprenhension.
>
> -r
>
>
>
> >> sys.exit()
>
> >> =============
>
> >> The problem is that when I launch it, python proggy is automatically
> >> suspended. The output I got is:
>
> >> roman at rslabs:~/pruebas$ ./shell.py
> >> roman at rslabs:~/pruebas$ uid=1000(roman) gid=1000(roman) groups=1000(roman)
> >> roman at rslabs:~/pruebas$
>
> >> [2]+  Stopped                 ./shell.py
> >> roman at rslabs:~/pruebas$
>
> >> Why and how to fix it? Would you suggest a better and more elegant way to
> >> do what I want?
>
> > As I see it, 'sh' is attempting to read from the keyboard and not from
> > stdin.
>
> > Karthik
>
> >> Thank you.
>
> >> --
>
> >> Saludos,
> >> -Roman
>
> >> PGP Fingerprint:
> >> 09BB EFCD 21ED 4E79 25FB  29E1 E47F 8A7D EAD5 6742
> >> [Key ID: 0xEAD56742. Available at KeyServ]
>
> > --
> >http://mail.python.org/mailman/listinfo/python-list
>
> --
>
> Saludos,
> -Roman
>
> PGP Fingerprint:
> 09BB EFCD 21ED 4E79 25FB  29E1 E47F 8A7D EAD5 6742
> [Key ID: 0xEAD56742. Available at KeyServ]




More information about the Python-list mailing list