Executing Shell commands using python In Linux

Question

So I just recently started having interest and playing CTF's on OverTheWire website and I am still in the first challenge called the bandit Lvl5 if you'll consider looking at it. So it teaches the use of linux command line etc

So here on this challenge I am tasked that there are hidden files in home directory I have to find them and in one of those files I will find a password to go to the next level taking note the are over 20 hidden files that come up.

So I then thought no man yes I can go through this manually but it will take forever so I tried making a script that I thought would work to get the hidden files and open one by one. But it does not work as I wanted.

I wanted to append those hidden files into a list and then run a for loop that will open each one of them and then I will be able to see results and spot password

Code Below

import os

a = []
for i in os.system('find .inhere/'):
    a.append(i)
for j in a:
    print("\n\n cat j ")

So it my first time messing code of such manner trying to interact with the command line using python can you please help on how I can go about it or if my code can be fixed

`os.system()` doesn't return the output of the command. Use `subprocess.Popen()` for this. And you need to split the output into lines, it's not done automatically for you. — Barmar, Jun 19 '20 at 22:06
Did you read the documentation? `os.system()` returns the exit status of the command. — Barmar, Jun 19 '20 at 22:06
Honestly never did read documentation on it came across this challenge few minutes back and ```os.system()``` came to mind, so I guess my mistake also could have be there on not reading the documentation — , Jun 19 '20 at 22:19

score -1 · Accepted Answer · edited Oct 23 '20 at 16:26

os.system() only returns the exit status of the command (Not the STDOUT). You should use the subprocess module especially the subprocess.Popen. I have added several comments for my code for the better understanding.

Code:

import subprocess
import sys


def call_command(command):
    """
    Call a command the STDOUT
    :param command: The related command
    :return: STDOUT as string
    """

    result1 = subprocess.Popen(
        command.split(), stdout=subprocess.PIPE, stderr=subprocess.PIPE, universal_newlines=True
    )

    #  Get the STDOUT and STDERR descriptors of the command.
    std_out, std_err = result1.communicate()

    return std_out


# Find files in test1 folder.
find_result = call_command("find test1/ -type f")
for one_find in find_result.split("\n"):
    if one_find:
        # The result of cat command will be in "cat_result" variable.
        cat_result = call_command("cat {}".format(one_find))
        print(cat_result)

        # You can write the result directly to STDOUT with the following line.
        # sys.stdout.write("\n".join(call_command("cat {}".format(one_find))))

Content of test1 folder:

>>> ll test1/
total 8
drwxrwxr-x  2 user grp 4096 Jul  8 14:18 ./
drwxrwxr-x 18 user grp 4096 Jul  8 14:33 ../
-rw-rw-r--  1 user grp 29 Jul  8 14:18 test_file.txt

Content of test_file.txt:

>>> cat test1/test_file.txt 
Contents of test_file.txt file

Output of the code:

>>> python3 test.py
Contents of test_file.txt file.

Actually you should prefer `subprocess.run()` over `Popen` if you can; this is clearly spelled out in the documentation. It basically saves you from having to reinvent `call_command` (which of course also duplicates the legacy `check_output` without the `check_` part which you should probably add anyway). — tripleee, Oct 23 '20 at 16:49
`command.split()` is also buggy; you should use `shlex.split(command)` instead, or simply pass in a list of strings. Perhaps see also [Actual meaning of `shell=True` in `subprocess`](https://stackoverflow.com/questions/3172470/actual-meaning-of-shell-true-in-subprocess) — tripleee, Oct 23 '20 at 16:53

Executing Shell commands using python In Linux

1 Answers1