In python, how do you input data from a list into a linux command?

Question

I'm trying to write a simple script that takes a list of words I've created in a text file on linux and runs it through a program that checks the word against a steganography extractor.

The program (steghide) uses the following syntax in the command:

steghide --extract -p {password here} -sf {filename here}

I've been able to call the file and set up a for loop for the words in the list, but can not find a way to input the word from that iteration into each command.

Here's how I've been trying to work it.

import os
import sys

script, filename = argv
filename2 = sys.open(filename)

for word in filename2:
    os.system('steghide --extract -p [want to put something here] -sf stegfilename')

I'm on a controlled box and can't download anything beyond what I already have. Any help is appreciated.

Update:

I got it to work. But now I'm trying to get it to exit out if it finds the correct answer. I am just having a hard time getting Python to read the output. Here's what I have so far.

`import subprocess from sys import argv

script, filename = argv passes = filename

with open(passes) as f: for line in f: proc = subprocess.popen(['steghide', '--extract', '-p' line.strip(), '-sf', 'stegged file name'],stdout = subprocess.PIPE) stdout = proc.communicate()[0] output = proc.stdout.readline()

    if 'wrote' in output:
        print 'YOU FOUND IT!'
        break
    else:
        print line`

Akshat Mahajan · Accepted Answer · 2016-04-12 23:09:20Z

1

This is a good time to learn string formating options in Python. They let you insert values dynamically into a string. An example:

"This {0} is an example".format([1,2,3])
>>>> "This [1,2,3] is an example"

In this particular case, you want to do

value = 'foo' # the item you want to insert - replace with list, number, etc.
...
for word in filename2:
    os.system('steghide --extract -p {0} -sf stegfilename'.format(value))

This will insert the value into your string, and then call steghide on that string.

answered Apr 12, 2016 at 23:09

Akshat Mahajan

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Comments

jDo · Accepted Answer · 2016-04-12 23:11:22Z

1

Use the subprocess module instead; it gives you more options/control and os.system() is deprecated.

import subproces
with open(filename, "r") as f:
    # assumes that you have one word per line
    for line in f:
        subprocess.call(['steghide', '--extract', '-p', line.strip(), '-sf', stegfilename])
        # or if you want the output of running Niels Provos' cool, old tool :)
        cmd_output = subprocess.check_output(['steghide', '--extract', '-p', line.strip(), '-sf', stegfilename])

answered Apr 12, 2016 at 23:11

jDo

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2 Comments

Brad Over a year ago

I got it to work, but now I'm trying to get it to exit once it finds the correct password. Here's what I have so far. import subprocess from sys import argv script, filename = argv passes = filename with open(passes) as f: for line in f: proc = subprocess.popen(['steghide', '--extract', '-p' line.strip(), '-sf', 'stegged file name'],stdout = subprocess.PIPE) stdout = proc.communicate()[0] output = proc.stdout.readline() if 'wrote' in output: print 'YOU FOUND IT!' break else: print line

jDo Over a year ago

@Brad steghide follows C/Unix conventions and returns 0 if successful, 1 if not. Use that along with subprocess.call to break on success (subprocess.call returns the return code of the process). No need for subprocess.PIPE, proc.communicate()[0] etc.

Padraic Cunningham · Accepted Answer · 2016-04-12 23:12:27Z

1

Use subprocess.check_call passing a list of args:

from subprocess import check_call


for word in map(str.rstrip, filename2):    
    check_call(['steghide', "--extract", "-p", word, "-sf", "stegfilename'"])

answered Apr 12, 2016 at 23:12

Padraic Cunningham

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Comments

Ajay2588 · Accepted Answer · 2017-07-13 11:45:17Z

0

String formatting is the subject here.

import os
import sys

script, filename = argv
filename2 = sys.open(filename)

for word in filename2:
    os.system('steghide --extract -p ' +[want to put something here]+ '-sf stegfilename')

answered Jul 13, 2017 at 11:45

Ajay2588

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Vitor Alves · Accepted Answer · 2019-09-27 20:12:04Z

0

To join all elements of a list in a string, try python join:

'  '.join(your_variable)

Example:

var = ['t', 't', 't', 't', 't', 't'] 
joined = ' '.join(var)
print(joined)
print(type(joined))

t t t t t t

class 'str'

answered Sep 27, 2019 at 20:12

Vitor Alves

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