[SOLVED] how to get linux command out outs in to a python script

[brijith]

Hai,

When I write scripts in python I use os.system() for executing linux commands . My doubt is, is there any method to get the output of the command in side the python script. What I usually do is redirect the out of the linux command in to a file and then read that file in side python script. Can any one suggest any other good method ?


Thanks

[ghostdog74]

Hai,

When I write scripts in python I use os.system() for executing linux commands . My doubt is, is there any method to get the output of the command in side the python script. What I usually do is redirect the out of the linux command in to a file and then read that file in side python script. Can any one suggest any other good method ?


Thanks

what linux commands are you executing?

[brijith]

what linux commands are you executing?

Let me explain my current requirement. I have to check super user privilege inside a python script. In the case of bash we can use id -ur or whoami to check the privilege. So if I am going to use any of these two in side a python script as os.system('id -ur') or os.system('whoami') I have to get the out put of these commands inside a python script. That is what I asked in the previous mail

Thanks

[Lau_of_DK]

Let me explain my current requirement. I have to check super user privilege inside a python script. In the case of bash we can use id -ur or whoami to check the privilege. So if I am going to use any of these two in side a python script as os.system('id -ur') or os.system('whoami') I have to get the out put of these commands inside a python script. That is what I asked in the previous mail

Thanks

Hey Brijith,

Like in C you can redirect the standard output io in Python. If I remember correctly its something like this



import sys, StringIO

mystdout = StringIO.StringIO()
sys.stdout = mystdout

os.system("ls")
stroutput = mystdout.getvalue()

sys.stdout = sys.__stdout__
print mystdout


Hope it flies,
/Lau :)

[brijith]

Hey Brijith,

Like in C you can redirect the standard output io in Python. If I remember correctly its something like this



import sys, StringIO

mystdout = StringIO.StringIO()
sys.stdout = mystdout

os.system("ls")
stroutput = mystdout.getvalue()

sys.stdout = sys.__stdout__
print mystdout


Hope it flies,
/Lau :)


I tried the code :



#!/usr/bin/env python
import sys, StringIO
import os

mystdout = StringIO.StringIO()
sys.stdout = mystdout

os.system("ls")
stroutput = mystdout.getvalue()
sys.stdout = sys.__stdout__

print 'mystdout :', mystdout # this is an istance of StringIO.StringIO, right ?
print 'stroutput :', stroutput # I think this variable contains the value


but the result is as shown below:


~/Desktop? python strio.py
12.tar.gz abc.txt CBQ data Deskop HOWTO new new file~ qwe smtptest.py strio.py tools
mystdout : <StringIO.StringIO instance at 0xb7d9ed6c>
stroutput :
~/Desktop?


The variable stroutput is empty



THANKS

[dtmilano]

However, os.getuid() maybe what you are looking for.

[brijith]

However, os.getuid() maybe what you are looking for.

Oky Thanks..


why the code didn't worked. if we could get the output of a bash in side a python it will be a great help.

Any why, thanks for os.getuid()

:)

[Lau_of_DK]

Oky Thanks..


why the code didn't worked. if we could get the output of a bash in side a python it will be a great help.

Any why, thanks for os.getuid()

:)

Hi again,

I'm sorry for posting code that flunked. I've tried on my own box and it gives the same result. The only explanation I can think of, is that os.system() does not print to sys.stdout. Maybe you can find a way to determine where it prints and the reroute it?

Another way to do it, which was posted on this forum earlier is:


>>> import os
>>> p = os.popen('ls')
>>> s = p.readline()
>>> p.close()
>>> print s
'direct rendering: Yes\n'
>>>



This should work? :)
Lau

[tested myself: it does work. Repeat readline until end of stream]

[brijith]

Thanks, this time it worked.

now I am getting the output in side python script. What about the error. if error occures it is coming in terminal but noting in p.readlines(). can we get the error message in side python script

Many Thanks

[Lau_of_DK]

Thanks, this time it worked.

now I am getting the output in side python script. What about the error. if error occures it is coming in terminal but noting in p.readlines(). can we get the error message in side python script

Many Thanks

I think if I were you, I'd look up the documentation on os. and sys. You might be able to solve this be redirecting sys.stderr like we tried with stdout, but its juts a guess :)

/Lau

[brijith]

You might be able to solve this be redirecting sys.stderr like we tried with stdout, but its juts a guess :)
/Lau
Yes I am trying each of os. and sys. entries It is very interesting

But when we tried sys.stdout it failed in what we needed. I think it will be the same for sys.stderr.

Oky Let me find out it..... :)

Thanks for clearing my doubts

[dtmilano]

Use (not tested, sorry):


p = subprocess.Popen("id -u", stdout=PIPE)
p.stdout.readline()

[strider1551]

Can any one suggest any other good method ?

I usually just use the commands module



import commands
output = commands.getoutput("ls")
print output

[RainCT]

I think subprocess.Popen is the best option (in terms of security). Below you have an example function which wrapps around it to make it more usable, so that you can look at it to see different ways of how you can use it (for example function allows stdout only, stderr only and both mixed together in order of appearance) or just feel free to use it directly.



def _get_output(self, command, stdout = True, stderr = False):
"""
Run the program specified in the first argument and return its output
as a string.
"""
if (stdout or stderr) and not (stdout and stderr):
pipe = subprocess.Popen(command, shell=True, stdout=subprocess.PIPE,
stderr=subprocess.PIPE)
if stdout:
return pipe.stdout.read()
else:
return pipe.stderr.read()
elif stdout and stderr:
return subprocess.Popen(command, shell=True, stdout=subprocess.PIPE,
stderr=subprocess.STDOUT).stdout().read()
else:
try:
return bool(subprocess.Popen(command))
except OSError:
print 'Error, could not execute the process.'
return None

[RainCT]

[Oops. Double post]

[pointone]

No need to reinvent wheels here...


import os
cmd_stdin, cmd_stdout, cmd_stderr = os.popen3("ls")
cmd_stdout.read()


import os
cmd_stdin, cmd_stdout, cmd_stderr = os.popen3("ls /non-existant_directory")
cmd_stdout.read() #returns nothing
cmd_stderr.read() #oh... there was an error!

More information... (http://docs.python.org/lib/os-newstreams.html)